摘要:

Journal of Materials Chemistry Scientific Advisory Editor Professor Martin R. Bryce Department of Chemistry University of Durham South Road Durham DHI 3LE, UK Associate Editor Professor Jean Etourneau ICMCB Avcnue du Docteur Schweitzer 33600 Pessac France Editorial board Allan E. Underhill (Chairman) Bungor Peter G. Bruce St. Andrews Martin R. Bryce Durhutn Jean Etourneau Bordeaux Managing Editor Janet L. Dean Deputy Editor Zoe G. Lewin Assistant Editor Graham F. McCann Editorial Secretary Miss D. J. Halls Wendy R. Flavell UMIST John W. Goodby Hull Klaus Praefcke Berlin Brian J. Tighe Aston International advisory editorial board K. Bechgaard Riso, Denmark J. Y. Becker Beer-Sheila, Isruel A. J. Bruce Murruy Hill, USA E.Chiellini Pisu, Ituly D. Coatcs Po&, UK P. Da? London, UK D. A. Dunmur Shefield, UK B. Dunn Los Angeles, USA W. J. Feast Durham, UK R. H. Friend Cunzhridge, UK A. Fukuda Tokyo, Jupun D. Gatteschi Florence, Ituly P. Hodge Munchester, UK Information for authors The Royal Society of Chemistry welcomes submission of manuscripts intended for publication in two forms, Articles and Materials Chemistry Communications. These should describe original work of high quality dealing with the synthesis, structures, properties and applications of materials, particularly those associated with advanced technology. Full papers contain original scientific work that has not been published previously. However, work that has appeared in print in a short form such as a Materials Chemistry Communication is normally acceptable.Four copies of Articles including a top copy with figures etc. should be sent to the Managing Editor at the Cambridge address. Journul of Muteritils Chemistry (ISSN 0959-9428) is published monthly by The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, UK. All orders accompanied with payment should be sent directly to The Royal Society of Chemistry, Turpin Distribution Services Ltd., Blackhorse Road, Letchworth, Herts SG6 1HN, UK. NB Turpin. Distribution Services Ltd.. distributors, is wholly owncd by The Royal Society of Chemistry. 1996 Annual subscription rate EEA (incl. UK) 5519.00: USA $934.00. Rest of World 5532.00.Customers A. B. Holmes Cambridge, UK H. Inokuchi Okazaki, Jupun W. Jeitschko Miinster, Germuny 0.Kahn Bordeaux, France J. Livage Paris, France R. McCullough Pittsburgh. USA J. S. Miller Salt Lake City, USA K. Mullen Muinz, Germany L. Niinisto Espoo, Finland M. Nygren Stockholm, Sweden Y. W. Park Seoul, Koreu N. Plate Moscow, Russin Materials Chemistry Communications contain novel scientific work in short form and of such importance that rapid publication is warranted. The total length is normally restrictcd to two printed A4 pages. However, special consideration will be given to communications with a large amount of essential diagramatic information. Submission of a Materials Chemistry Communication can be made either to the Managing Editor at the Cambridge address, or ciu a member of the International Advisory Editorial Board.In the latter case, the top copy of the manuscript including any figures etc., togcther with the name of the person to whom the Communication is being submitted, should be sent simultaneously to the Managing Editor at the Cambridge address. All authors submitting work for publication are should make payments by cheque in sterling payable on a UK clearing bank or in US dollars payable on a US clearing bank. Air freight and mailing in the USA by Publications Expediting Inc., 200 Meacham Avenue, Elmont, NY 11003. 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All submissions should be accompanied by a completed form (a blank for photocopying is reproduced at the end of the Information for Authors in Issue l),without which publication cannot proceed. A completed graphical abstract template should also accompany each submission. Full details of the form of manuscripts for Articles and Materials Chemistry Communications, conditions for acceptance etc. are given in Issue 1 of Journul of Materials Chemistry published in January of each year, on the world wide web (htpp://chemistry.rsc.org/rsc/)or may be obtained from the Managing Editor. There is no page charge for papers published in Journul of Materials Chemistry. Fifty reprints are supplied free of charge. Janet L. Dean, Managing Editor Tel.: Cambridge (01223) 420066 E-Mail (INTERNET): DEANJ@RSC.ORG Fax: (01223) 420247 Advertisement sales: Tel. +44 (0)171-287 3091; Fax +44 (0)171-494 1134 0The Royal Society of Chemistry, 1996. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form, or by any means, electronic, mechanical, photographic, recording, or otherwise, without the prior permission of the publishers.

ISSN:0959-9428    

DOI:10.1039/JM99606FX005

出版商:RSC    

年代:1996

数据来源: RSC

ISSN:0959-9428    

DOI:10.1039/JM99606BX007

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

ISSN 0959-9428 JMACEP(6) 5 11-676 ( 1996) Synthesis, structures, properties and applications of materials, particularly those associated with advanced technology Feature Article 5 11 Hybrid organic-inorganic materials: a land of multidisciplinarit y Patrick Judeinstein and Clement Sanchez -v Pv+ $*- Articles 527 Synthesis of polyesters containing 9,lO- diacetoxyanthracene-2,6-diyl moieties via a precursor polymer approach Ruab Uddin, Philip Hodge, Michael S. Chisholm and Paul Eustace 5 33 Paramagnetic liquid-crystal side-chain polyacrylates containing Schiff-base copper (11 ) complexes Eduardo Campillos, Mercedes Marcos, Jose Luis Serrano, Pablo J. Alonso and Jesus I. Martinez 539 Molecular motions near the glass transition in diethylene glycol bis (ally1 carbonate) as studied 06 by dielectric relaxation spectroscopy 04 *r Ian K.Smith, Stuart R. Andrews, 02 Graham Williams and Paul A. Holmes 00 1 547 Structure, dielectric relaxation and electrical conductivity of 2,3,7,8-tetramethoxy- chalcogenanthrene-2,3-dichloro-5,6-dicyano-1,4-benzoquinone1:1charge-transfer complexes Ulrich Behrens, Ricardo Diaz Calleja, Mark Dotze, Ursula Franke, Walter GunBer, Gunter Klar, Jens Kudnig, Falk Olbrich, Enrique Sanchez Martinez, Maria J Sanchis and Barbel Zimmer 555 Boron derivatives containing a bithiophene bridge as new materials for non-linear optics Catherine Branger, Minh Lequan, Rose Marie Lequan, Marguerite Barzoukas and Alain Fort 559 Synthesis and physical performance of indole and benzimidazole cyanine dyes Zheng-Hong Peng, Li Qun, Xiang-Feng Zhou, Suzanne Carroll, Herman J Geise, Bi-Xian Peng, Roger Dommisse and Robert Carleer 567 Investigation of the formation of Ru0,-based mixed oxide coatings by secondary ion mass spectrometry Sergio Daolio, Janos Kristof, Clara Piccirillo, Cesare Pagura and Achille De Battisti 573 Preparation of colloidal silver dispersions by the polyol process.Part 1.-Synthesis and characterization Pierre-Yves Silvert, Ronald0 Herrera-Urbina, Nicolas Duvauchelle, Venugopal Vijayakrishnan and Kamar Tekaia Elhsissen 579 Coordination environment of copper(11) during the sol-gel process of an aminated alkoxide Andrzej M Klonkowski, Klaus Koehler, Teresa Widernik and Beata Grobelna Vn2E2-DDQ(E= S Se) 1 2 3 0 10 20 30 40 50 60 70 60 90 100 drarnete r/nm d 6 11 585 Pyrolysis study of methyl-substituted Si-H containing gels as precursors for oxycarbide glasses, by combined thermogravimetry, gas chromatographic and mass spectrometric analysis Renzo Campostrini, Gennaro D'Andrea, Giovanni Carturan, Riccardo Ceccato and Gian Domenico Soraru 595 Structure of carbon produced by hydrothermal treatment of P-SiC powder Yury G.Gogotsi, Klaus G. Nickel, Djamila Bahloul-Hourlier, Therese Merle-Mejean, Galina E. Khomenko and Kjell P. Skjerlie 605 A carbon-bearing nickel(u) ferrite: a tailor- made solid reactant for two-step thermochemical water splitting at 300 'C T.Sano, N. Hasegawa, M. Tsuji and Y. Tamaura 61 1 Solvothermal synthesis and structural characterisation of the first ammonium cobalt gallium phosphate hydrate, NH, [CoGazP3Oi2(H20)21 Ann M. Chippindale, Andrew R. Cowley and Richard I. Walton 615 Correlating thermochemical data of the oxygen non-stoichiometric compound YBa,Cu,O, -x with the oxygen content Hengzhong Zhang, Pingmin Zhang and Xinmin Chen 619 The YBa,Cu,O, phase diagram Christian Picard and Paul Gerdanian TG+GC+MS coupled analysis I) h 'U T=60O-80O0C,P=100-500MPa CBNF 02 CBNF* \ 1nickel (11) ferrite H2 A,H" (n,298 K) = -2097.20 -80.42~kJ mol-' So(n,298 K) = -1253.43 f458.80n -33.42n2J mol-K-' CJn, TK)=230.62+ 14.98n+(-468.86+2.09n) x 10-3 ~+(47.61-0.84n) x 105 T-2 +794.18 x T2 J mol-' K-' II Phuc Diagnm ...623 LuBa2Cu30, -thin films prepared using MOCVD Sergey V. Samoylenkov, Oleg Yu. Gorbenko, Igor E. Graboy, Andrey R. Kaul and Yury D. Tretyakov 629 Unit-cell symmetries and Raman spectra of calcium- and neodymium-doped barium cerate proton-conducting ceramic electrolytes Robert C. T. Slade, Sara D. Flint, Alison Holloway, Narendra Singh, Lubomir Smrcok and Daniel Tunega 635 Magnetic, electrical and '"Eu Mossbauer properties of EuPtGe Rainer Pottgen, Reinhard K. Kremer, Walter Schnelle, Ralf Miillmann and Bernd D. Mosel 639 Synthesis and crystal structures of two metal phosphonates, M(HO,PC,H,), (M =Ba, Pb) Damodara M.Poojary, Baolong Zhang, Aurelio Cabeza, Miguel A. G. Aranda, Sebastian Bruque and Abraham Clearfield 645 Protonation and olation of 2,2'-bipyridyl and 1,lO-phenanthroline in y-titanium phosphate dihydrate Carla Ferragina, M. Antonietta Massucci and Anthony A. G. Tomlinson 653 Computer modelling of V,O,: surface structures, crystal morphology and ethene sorption Dean C. Sayle, David H. Gay, Andrew L. Rohl, C. Richard A. Catlow, John H. Harding, Marc A. Perrin and Patrice Nortier TIK 50 50.5 51 51.5 2Oldegrees iv I 661 Ordering and manipulation of MoS, platelets on differently charged micas by atomic force microscopy Suzanne Mulley, Angelo Sironi, Adriana De Stefanis and Anthony A.G. Tomlinson Materials Chemistry Communications 667 Supermolecular alignment in a liquid crystal- polymer gel as studied optically and by dielectric relaxation spectroscopy Monica M. Marugan, Sara Shinton and Graham Williams Aligned LC / Monomer Aligned LC Gel 671 Thresholdless antiferroelectricity in liquid I.o crystals and its application to displays Shiroh Inui, Noriko Iimura, Tsuyoshi Suzuki, Hiroshi Iwane, Kouichi Miyachi, Yoichi Takanishi and Atsuo Fukuda 0.0-6 -4 -2 0 2 4 6 electricfielw pm-' 675 Striking effects of halogen substituents on the glass-forming properties, glass-transition temperatures and stabilities of the glassy state of a new family of amorphous molecular materials, X 1,3,5-tris(4halogenophenyl-X = F, Cl, Bro,,,&l..Nophen y lamino) benzenes Hiroshi Kageyama, Koji Itano, Wataru Ishikawa and Yasuhiko Shirota i Cumulative Author Index iii Conference Diary Note: Where an asterisk appears against the name of one or more authors, it is included with the authors' approval to indicate that correspondence may be addressed to this person. COPIES OF CITED ARTICLES The Royal Society of Chemistry Library can usually supply copies of cited articles.For further details contact: The Library, Royal Society of Chemistry, Burlington House, Piccadilly, London W1V OBN, UK. Tel: +44 (0)171-437 8656, Fax: +44 (0)171-287 9798, Telecom Gold 84: BUR210, Electronic Mailbox (Internet) LIBRARY@RSC.ORG. If the material is not available from the Society's Library, the staff will be pleased to advise on its availability from other sources. Please note that copies are not available from the RSC at Thomas Graham House, Cambridge. V

ISSN:0959-9428    

DOI:10.1039/JM99606FP015

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Cumulative Author Index 1995 Alcantara-Rodriguez M., 247 Ali F., 261 De Battisti A., 567 de Lacy Costello B. P. J., 289 Huang K-S., 123 Hudson M. J., 49, 89 Humberstone P., 315 Mattei G., 403 McKeown N. B., 315 McLendon G., 369 Saito K., 501 Salvad6 M. A., 415 Salvador S., 73 Ali-Adib Z., 15 Allen J. L., 165 Alonso P. J., 533 Al-Raihani H., 495 Delmas C., 193 de Souza D. P. F., de Souza M. F., 233 De Stefanis A., 661 233 Ihanus J., 161 Iimura N., 671 Ikemoto I., 501 Imae I., 117 McMurdo J., 149 Mercey B., 165 Merle-Mejean T., 595 Michel C., 175 Samoylenkov S. V., 623 Sanchez C., 511 Sanchez L., 37 Sanchis M. J., 547 Andrews S. R., 539 Arai H., 455 Arai K., 11 Aranda M. A. G., 639 Arriortua M. I., 421 Ashwell G. J., Attfield J. P., 57 Bahloul-Hourlier D., 595 Bahra G.S., 23 Barberis G. E., 421 Bardosova M., 375 Barrans Y., 5 Barrel1 K. J., 323 Barton J. M., 305 Barzoukas M., 555 Bassoul P., 5 Bast1 Z., 155 Battle P. D., 201, 395 Baur W. H., 271 Bay B. H., 331 Behrens U., 547 Berry F. J., 221 Beteille F., 505 Bieniok A., 271 Blin J. L., 385 Bomben A., 15 Bornholdt K., 271 Boutinaud P., 381 Boyle D. S., 227 Branger C., 555 Bravic G., 5 Breen C., 253 Brendel U., 271 Britton D., 123 Brown C. R., 23 Bruque S., 639 Bukhtenko 0.V., 207 Bush T. S., 395 Bushnell-Wye G., 337, 449 Byrn S. R., 123 Cabeza A., 639 Cabrera S., 175 CaldCs M. T.,. 175 Calleja R. D., 547 Campbell S. A., 295 Campillos E., 349, 533 Campostrini R., 585 Carleer R., 559 Carroll S., 559 Carturan G., 585 Catlow C. R. A., 653 Ceccato R., 585 Chane-Ching K., 5 Charters R.B., 131 Chassagneux F., 495 Chasseau D., 5 Chen J., 465 Chen X., 1, 615 Chippindale A. M., 611 Chisholm M. S., 527 Choi J. U., 365 Chung D. D. L., 469 Chung H., 365 Clarkson G. J., 315 Clearfield A,, 639 Cole-Hamilton D. J., 507 Cook M. J., 149 Cooke S., 1 Cowley A. R., 611 Crayston J. A., 187 DAndrea G., 585 Daolio S., 567 Davies A., 49 Davies T. W., 73 Davis F., 15 Davis S. J., 479 Dawson D. H.. 409 23, 131, 137 Dirken P. J., 337 Domingues-Rodrigues Dommisse R., 559 Dotze M., 547 Dragone R., 403 Durand B., 495 Dussack L. L., 81 Duvauchelle N., 573 Eadon D., 221 Eguchi K., 455 Elhsissen K. T., 573 Ellert 0.G., 207 Enoki T., 119 Enomoto M., 119 Etter the late M. C., Eustace P., 527 Evans P., 289, 295 Ewen R. J., 289 Farcy J., 37 Farr I. V., 103 Ferragina C., 645 Flint S.D., 629 Fort A., 555 Foster D. F., 507 Franke U., 547 Franklin K. R., 109 Fukuda A., 671 Ganguli M., 391 Gao Y., 369 Garcia J. R., 415 Garcia-Granda S., 415 Gay D. H., 653 Gazzoli D., 403 Geise H. J., 559 Gentle I. R., 137 George C. D., 131 Gerdanian P., 619 GIenis S., 1 Gogotsi Y. G., 595 Gomi Y., 119 Goiii A., 421 Gorbenko 0.Y., 623 Gore J. G., 201 Graboy I. E., 623 Green D. A., 449 Grobelna B., 579 Grobet P., 239 GunDer W., 547 Guzman G., 505 Hahn J. H., 365 Hall S. B., 183 Hamada D., 69 Hamerton I., 305, 311 Hamet J-F., 165 Hamilton D. G., 23 Harding J. H., 653 Harkema S., 357 Harrison W. T. A,, 81 Hasegawa N., 605 Hayashi H., 459 Heald R. C., 311 Hernan L., 37 Herrera-Urbina R., 573 Hersans R., 149 Hervieu M., 165, 175 Hitch T. J.A. R., 285 Hobson R. J., 49 Hodge P., 15, 375, 527 Hoffmann R-D., 429 Holloway A., 629 Holloway J., 221 Holmes P. A., 539 Honeybourne C. L., 277, Howlin B. J., 305, 311 A,, 207 123 GUO L-H., 369 285, 289, 323 Ingram-Jones V. J., 73 Inman D., 495 Inoue H., 455 Inui S., 671 Ishikawa W., 675 Itano K., 675 Iwane H., 671 Iyoda M., 501 Jackson P. D., 137 Jacobson A. J., 81 James M., 57 Janes R., 183 Jansson K., 97, 213 Jarmo Koivusaari K., 449 Jefferies G., 131, 137 Jimenez-Lopez E. R- C. A., 247 Jones J. R., 305 Judeinstein P., 511 Jumas J-C., 41 Kaczorowski D., 429 Kagawa S., 97 Kageyama H., 675 Kanamura K., 33 Kanniainen T., 161 Katerski A,, 377 Kaul A. R., 623 Kawaguchi K., 117 Kennard C. H. L., Khomenko G. E., 595 Kikuchi K., 501 Kim J. H., 365 Kim S. B., 365 Kitazawa T., 119 Klar G., 547 Knowles J.A., 89 Kochubey D. I., 207 Koehler K., 579 Koto K., 459 Kremer R. K., 635 Kristof J., 567 Kudnig J., 547 Kuroda K., 69 Ktonkowski A. M., 579 Labes M. M., 1 Lai S-W., 469 Lavela P., 41 Lee C. K., 331 Lee E., 109 Lee G. R., 187 Le Flem G., 381 Lequan M., 5, 555 Lequan R. M., 5, 555 Lerner M. M., 103 Leskela M., 161 Lezama L. M., 421 Lin C. L., 1 Lin J., 265 Lindroos S., 161 Liu S., 305 Livage J., 505 Llavona R., 415 Lorriaux-Rubbens A., 385 Lowendahl L., 213 Lynch D. E., 23 Machida M., 69, 455 Macklin W. J., 49 Maksimov Y. V., 207 Mann B. E., 253 Marcos M., 349, 533 Martinez E. S., 547 Martinez J. I., 533 Marucci A., 403 Marugan M. M., 667 Massucci M. A., 645 MatijeviC E., 443 Matsuyama H., 501 23, 137 Minami T., 459 Miyachi K., 671 Miyazaki A,, 119 Moffat J. B., 459 Moine B., 381 Monk P.M. S., 183 Moon J. H., 365 Morales J., 37, 41 Mori T., 501 Moriga T., 459 Morineau R., 505 Mosel B. D., 635 Mulley S., 661 Mullmann R., 635 Naito H., 33 Nakano H., 117 Neat R. J., 49 Newport R. J., 337, 449 Nickel K. G., 595 Nieminen M., 27 Nii H., 97 Niinisto L., 27 Noma N., 117 Nortier P., 653 Nygren M., 97 OBrien P., 343 Ogawa K., 143 Ohyama T., 11 Olbrich F., 547 Olivera-Pastor P., 247 Olivier-Fourcade J., 41 Omenat A., 349 Oriakhi C. O., 103 Otterstedt J-E., 213 Pac C., 143 Pagura C., 567 Parent C., 381 Park J. W., 365 Partridge R. D., 183 Pedrini C., 381 Peeters K., 239 Pelloquin D., 175 Peng B-X., 559 Peng Z-H., 559 Pereira-Ramos J-P., 37 Perrin M-A,, 653 Pertierra P., 415 Petrunenko I. A., 207 Picard C., 619 Piccirillo C., 567 Pickett N.L., 507 Pizarro J. L., 421 Pola J., 155 Poojary D. M., 639 Pottgen R., 63, 429, 635 Prellier W., 165 Qian M., 435 Qun L., 559 Ranjan R., 131 Rao K. J., 391 Rasheed R. K., 277 Rasika Abeysinghe J., 155 Ratcliffe N. M., 289, 295, 30 1 Rauhala E., 27 Raveau B., 165, 175 Rawson J. O., 253 Razafitrimo H., 369 Rigden J. S., 337, 449 Rodriguez J., 415 Rodriguez M. L., 415 Rodriguez-Castellbn E., Rohl A. L., 653 Rojo T., 421 Russell D. A., 149 Saadoune I., 193 247 Sanders G. M., 357 Sano T., 605 Sasaki S., 501 Sayle D. C., 653 Schnelle W., 635 Schouten P. G., 357 Segal N., 395 Serrano J. L., 349, 533 Shinton S., 667 Shirota Y., 117, 675 Shitara Y., 11 Silvert P-Y., 573 Singh N., 629 Sironi A,, 661 Skjerlie K. P., 595 Slade R.C. T., Smart L. E., 221 Smith I. K., 539 Smith J. R., 295 Smith M. E., 261, 337 Smrcok L., 629 Sorarh G. D., 585 Southern J. C., 73 Steuernagel S., 261 Stoev M., 377 Su Q., 265 Suirez M., 415 Subrt J., 155 Sudholter E. J. R., 357 Sugahara Y., 69 Sugiyama S., 459 Suzuki H., 501 Suzuki T., 671 Takahashi M., 119 Takanishi Y., 671 Takeda M., 119 Takehara Z-I., 33 Tamaura Y., 605 Tanaka M., 459 Tatam R. P., 131 Taylor R., 155 Teare G. C., 301 Teraoka Y., 97 Teunis C. J., 357 Tirado J. L., 37, 41 Tomkinson J., 449 Tomlinson A. A. G., 645, Torncrona A,, 213 Tran V. H., 429 Treacher K. E., 315 Tredgold R. H., 375 Tretyakov Y. D., 623 Trindade T., 343 Troc R., 429 Tsodikov M. V., 207 Tsuji M., 605 Tundo P., 15 Tunega D., 629 Uddin R., 527 Vaidhyanathan B., 391 Valigi M., 403 Valli L., 15 van de Velde G.M. H., van Dijk M., 357 Vansant E. F., 239 Vaughey J. T., 81 Vente J. F., 395 Vijayakrishnan V., 573 Vogt T., 81 Wallart F., 385 Walton R. I., 611 Wang S., 265 Warman J. M., 357 Watts J. F., 479 West A. R., 331 73, 629 661 357 1 Whitfield H. J., 261 Williams G., 539, 667 Yao J., 143 Yue Y., 465 Zhang P., 615 Widernik T., 579 Winfield J. M., 227 Yao T., 33 Zeng H. C., 435 Zhong Q., 443 Wignacourt J. P., 385 Woolley M., 375 Yonehara H., 143 Zhang B., 639 Zhou X-F., 559 Williams D. E., 409 Xu R., 465 Yoshino H., 501 Zhang H., 265, 615 Zimmer B., 547 11 Conference Diary May 2-7 Metal Clusters in Chemistry Strasbourg, France Dr Josip Hendekovic, European Science Foundation, 1quai Lezay-Marnesia, 67080 Strasbourg Cedex, France.E-mail: euresco@esf.c-strasbourg.fr; Tel: +33 88 76 71 35; Fax: +33 88 36 69 87. May 6-10 Second European Solid Oxide Fuel Cell Forum Oslo, Norway European SOFC Secretariat, PO Box 1929, CH-5400 Baden, Switzerland. Fax: +41 56 218466. May 12-15 Fifth European Symposium on Polymer Blends Maastricht, The Netherlands E. MeurisiM. Keulen, P.O. Box 5511, 6202 XA Maastricht. The Netherlands. Tel: +31 46 767252/761596; Fax: +31 46 767605. May 18-24 IS&T 49th Annual Conference Minneapolis, MN, USA Conference Manager, IS&T, 7003 Kilworth Lane, Springfield, VA 22151, USA. E-mail: imagesoc@us.net; Tel: +1 703 642 9090; Fax: +1 703 642 9094. May 27-31 The Polymer Processing Society 12th Annual Meeting Sorrento, Italy Professor Jose M.Kenny, 12th PPS Meeting, Department of Materials and Production Engineering, University of Naples, P. Tecchio, 80125 Naples, Italy May 29/31 International Symposium on Nitrides Saint-Malo, France Professor P Verdier, ISN'T Secretary, U.R.A. "Verres et Ceramiques" Universite de Rennes I. Av. General Leclerc. 35042 -Rennes Cedex, France. June 1996 International Conference on Intelligent Materials Lyon, France Mrs Claude Bernavon ICIM 96, Group d'Etudes de Metallurgie Physique et de Physique de Materiaux, Biit. 502 -ler etage, Institut National des Sciences Appliques de Lyon, 20 avenue Albert Einstein, F 69621 Villeurbanne Cedex, France. E-mail: bernavon@insa.insa-1yon.fr;Tel: +33 72 43 S3 85; Fax: +33 72 43 88 30.June 3-6 Dedicated Conference on Materials for Energy-Efficient Vehicles Florence, Italy The ISATA Secretariat, 42 Lloyd Park Avenue, Croydon CRO 5SB. UK. E-mail: 100270.1263@COMPUSERVE.COM;Tel: +44 181 681 3069; Fax: +44 181 686 1490 June 3-7 4th World Surfactants Congress Barcelona, Spain J. Sanchez Leal, General Secretary, CESIO AEPSAT, Comite Espanol de la Detergencia (CED). -Jordi Girona, 18-26. 08034 Barcelona, Spain. E-mail: cesio96@cid.csic.es; Tel: (343) 204 02 12 -400 61 00; Fax: (343) 280 53 00 -204 59 04. June 8-13 Fundamental Aspects of Surface Science: Semiconductor Surfaces Blankenberge, Belgium Dr Josip Hendekovic, European Science Foundation, 1quai Lezav-Marnesia, 67080 Strasbourg Cedex, France. E-mail: euresc0Oesf.c-strasbourg.fr;Tel: +33 88 76 71 35; Fax: +33 88 36 69 87.June 10-13 Science and Technology of Pigment Dispersion Luzern, Switzerland Dr A. V. Patsis, Director, Institute for Materials Science, State University of New York, New Paltz, NY 12561, USA. Tel: +914 255 0757; Fax: +914 255 0978. June 17-19 18th International Conference in Stabilization and Controlled Degradation of Polymers Luzern, Switzerland Dr A.V. Patsis, Director, Institute for Materials Science, State University of New York, New Paltz, Ny 12561, USA. Tel: +914 255 0757; Fax: +914 255 0978. June 24-28 ILCC: 16th International Liquid Crystal Conference Kent, OH, USA 16th International Liquid Crystal Conference, Liquid Crystal Institute, Kent State University, P.O. Box 5190, Kent, OH 44242-0001, USA.E-mail: ILCC16Oalice.kent.edu; Tel: +1216 672 2654; Fax: +1 216 672 2796. June 24-28 1lth Bratislava IUPAC International Conference on Polymers High Tatras Bratislava, Slovakia Dr Lyda Rychla, Polymer Institute, Slovak Academy of Sciences, Dubravska cesta, CS 842-36 Bratislava, Slovakia. E-mail: upolrych@savba.sk; Tel: 0042 7 37 34 48; Fax: 0042 7 37 59 23. June 26-28 TMS, 1996 38th Electronic Materials Conference The Minerals, Metals & Materials Society (TMS), 420 Commonwealth Drive, Warrendale, PA 15086, USA E-mail: csc&ms.org; Tel: 412-776-9000; Fax: 412-776-3770 July 1-5 22nd International Conference in Organic Coatings -Waterborne, High Solids, Powder Coatings Athens, Greece Dr A.V. Patsis, Director, Institute for Materials Science, State University of New York, New Paltz, Ny 12561, USA.Tel: +914 155 0757; Fax: +914 255 0978. July 6-12 Solid State Chemistry '96 Bratislava, Slovak Republic SSCH '96, Institute of Inorganic chemistry, Slovak Academy of Sciences, SK-842 36 Bratislava, Slovak Republic ... 111 July 7-12 XVIIth International Conference Organometallic Chemistry Brisbane, Australia XVIIth ICOMC Secretariat, Faculty of Science and Technology, Griffith University, Brisbane 4111, Australia. E-mail: ICOMC@sct.gu.edu.au; Tel: +61 (017 3875 7217; Fax: +61 (017 3875 7656. July 8-10 ESOPS 12 -"12th European Symposium on Polymer Spectroscopy" Lyon, France Dr G. Lachenal, Universite Lyon 1,Laboratoire des Materiaux Plastiques, Bld du 11Novembre 69622 Villeurbame, Cedex France.E-mail: lachenal@niatplast.univ-lyon1.fr; Tel: +33 72 43 12 11; Fax: +33 72 43 12 49. July 29-Recent Advances in Polymer Synthesis August 2 York, UK Professor P. Hodge, Department of Chemistry, University of Manchester, Oxford Road, Manchester, UK M13 9pL. E-mail: Philip.Hodge@man.ac.uk; Tel: +44 (0)161 275 4706; Fax: +44 (0) 161 275 4598. August 4-9 IUPAC MACRO SEOUL '96: 36th IUPAC International Symposium on Macromolecules Seoul, Korea Dr. Kwang Ung Kim, Secretariat of IUPAC MACRO SEOUL '96, Division of Polymers, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, Korea. E-mail: iupac@kistmail.kist.re.kr;Tel: +82 2 957 6104; Fax: +82 2 957 6105. August 4-9 The Tenth American Conference on Crystal Growth Colorado, USA Anthony L.Gentile, American Association for Crystal Growth, PO Box 3233, Thousand Oaks, CA 91359-0233 USA Fax: 805 492 4062 August 28-31 loth Conference of the European Society of Biomechanics Leuven, Belgium Dr. J. Vander Sloten, Executive Secretary, 10th Conference of the European Society of Biomechanics, Katholieke Universiteit Leuven, Division of Eiomechanics and Engineering Design, Celestijnenlaan 200A, B-3001 Heverlee, Belgium. E-mail: jos.vandersloten@mech.kuleuven.ac.be;Tel: +32 16 32 70 96; Fax: +32 16 29 27 16. September 1-6 XIth International Symposium on Organosilicon Chemistry Montpellier, France Professor R.J.P. Corriu, Laboratoire des Precurseurs Organonietalliques de Materiaux, UMR CNRS 44, Universite de Montpellier 11, Place E.Bataillon, CC 007, F34095 Montpellier Cedex 5, France Fax: +67 14 38 88. September 1-6 ECME 96, Third European Conference on Molecular Electronics Leuven, Belgium Professor F.C. De Schryver, Department of Chemistry, K.U. Leuven, Celestijnenlaan 200 F, B-3001 Heverlee, Belgium. September 9-10 Molecular Modelling of Chemicals and Materials Amsterdam, The Netherlands Dr A.M. Brouwer, Laboratory of Organic Chemistry, Amsterdam Institute of Molecular Studies (AIMS), Nieuwe Achtergracht 129, 1018 WS Amsterdam, The Netherlands. E-mail: mgms@chem.uva.nl; Fax: 31(0)20 5255670; WWW page: http://krop.chem.uva.nl/mgms/ October 9-14 Physical Metallurgy: Interfacial Engineering in Materials Castelvecchio Pascoli, Italy Dr Josip Hendekovic, European Science Foundation, 1 quai Lezay-Marnesia, 67080 Strasbourg Cedex, France.E-mail: euresco0esf.c-strasbourg.fr; Tel: +33 88 76 71 35; Fax: +33 88 36 69 87. October 13-18 ISLC '96 15th International Semiconductor Laser Conference Haifa, Can Carmel, Israel IEEELEOS, 445 Hoes Lane, P.O. Box 1331, Piscataway, NJ 08855-1331, USA. Tel: +1908 562 3898; Fax: +1 908 562 8434. October 27-12th International Congress on Advances in Non-Impact Printing Technologies November 1 San Antonio, TX, USA Conference Manager, IS&T, 7003 Kilworth Lane, Springfield, VA 22151, USA. E-mail: imagesoc@s.net; Tel: +1 703 642 9090; Fax: +1 703 642 9094. November 16-23 IS&T/SID Fourth Color Imaging Conference: Color Science, Systems & Applications Scottsdale, AZ, IJSA Conference Manager, IS&T, 7003 Kilworth Lane, Springfield, VA 22 151, USA. E-mail: imagesoc@s.net; Tel: +1 703 642 9090; Fax: +1 703 642 9094. July 14-18 The 3rd International Conference on Materiak Chemistry University of Exeter, UK August 24-27 ZMPC '97 International Symposium on Zeolites and Microporous Crystals Tokyo, Japan Dr Takahashi Tatsumi, Secretary, ZMPC '97, Engineering Research Institute, Faculty of Engineering, The University of Tokyo, Yayoi, Tokyo 113, Japan. Denotes a new or amended entry this month. Entries in the Conference Diary are published free of charge. If you wish to include an announcement please send full details to: Journal of Materials Chemistry Editorial Office, Thomas Graham House, Science Park, Milton Road, Cambridge, UK, CB4 4WF. Tel: +44 1223 420066; Fax:+44 1223 426017. 1v

ISSN:0959-9428    

DOI:10.1039/JM99606BP021

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Hybrid organic-inorganic materials a land of multidisciplinarity Patrick Judeinstein*' and ClCment Sanchez 'Laboratoire de Chimie Structurale Organique (URA 1384) Bdt. 0 Universitt! Paris Sud Orsay France bLaboratoire de Chimie de la Matiire Condensie (URA 1466) Universiti P. et M. Curie 4 Place Jussieu 75252 Paris Cedex France Organic-inorganic hybrids appear as a creative alternative for obtaining new materials with unusual features. This is related to their diphasic structures leading to multifunctional materials. The low-temperature processes which are used to synthesize such structures provide a wide versatility in the design of the compounds. The potentiality of the chemistry is to play on the structure of these mixtures and dissociate the various contributions in tailoring both phases and controlling the interfaces.In this paper a review of some chemistry pathways to hybrid materials is presented. The nature of the bonds between organic and inorganic phases is used to divide them in two major families class I corresponds to materials with weak interphase bonding while class I1 corresponds to materials where both phases are chemically grafted. Applications of these materials in the fields of optics iono- electronics mechanics biology and others are expected. Some applications are reviewed with respect to the versatility of the synthetic procedure. Most of the properties of these new high-technology materials are dependent on their structural and chemical composition as well as on the dynamical properties inside the blends.The possibility of combining the properties of organic and inorganic compounds in a unique material is an old challenge that started with the beginning of the industrial era. Some of the oldest and most famous organic-inorganic hybrids come from the paint industries where inorganic pigments (TiO etc.) are suspended in organic mixtures (solvents surfactants etc.). While the concept of 'hybrid' materials was not mentioned at that time the wide increase of work on organic-inorganic structures continued with the development of the polymer industry. Inorganic fillers (minerals clays talcs etc.) were added to polymers in order to improve some of the properties of the compounds. In fact the concept of 'hybrid organic- inorganic' materials emerged only very recently when the research shifted to more sophisticated materials with a higher added value.',2 Recently the study of organic-inorganic nano-composites networks and gels became an expanding field of in~estigation.~,~These new materials considered as innovative advanced materials promise new applications in many fields such as optics electronics ionics mechanics and biology.At first glance these materials are considered as biphasic mate- rials where the organic and inorganic phases are mixed at thenm to sub-pm scales. Nonetheless it is obvious that the properties of these materials are not just the sum of the individual contributions from both phases; the role of the inner interfaces could be predominant.The nature of the interface has been used recently to divide these materials into two distinct classes.' In class I organic and inorganic compounds are embedded and only weak bonds (hydrogen van der Waals or ionic bonds) give the cohesion to the whole structure. In class I1 materials the two phases are linked together through strong chemical bonds (covalent or iono-covalent bonds). Obviously within many class I1 hybrid materials organic and inorganic components can also interact via the same kind of weak bonds that define the class I hybrids. Generally the organics are 'fragile' and their thermal stability is limited to less than 250°C meaning that high temperatures are prohibited during the hybrid formation process. The sol-gel process overcomes this limitation.6 Inorganic polymerizations are performed around ambient temperature starting with metallo-organic precursors (salts or alkoxides).Metal-oxo based macromolecular networks are formed after hydrolysis- condensation reactions. The choice of reaction conditions leads to the control of the material structure and properties.' The basic background for the sol-gel chemistry will be described first. Then general methods for the production of class I and class I1 hybrid materials will be presented. Finally some applications of these hybrid materials will be outlined emphasizing the flexibility of the process which adjust the properties of the final materials. Chemistry Synthesis of Hybrid Materials Sol-gel processes Sol-gel processes are a method of forming dispersed inorganic materials in solvents through the growth of metal-oxo poly- mer~.~'~The chemistry is based on inorganic polymerization reactions.Metal alkoxides [M(OR) where M=Si Sn Ti Zr Al Mo V W Ce etc.; OR an alkoxy group OC,H2,+ J are used as molecular precursors which lead to metal-oxo polymers through hydrolysis and condensation reactions. The first step in sol-gel synthesis is the hydroxylation of the metal alkoxide which occurs upon hydrolysis of the alkoxy groups as follows M-OR +H20+M-OH +ROH Reactive hydroxy groups are generated first. They then undergo polycondensation reactions via two competing mechanisms (a) Oxolation the formation of an oxygen bridge M -OH +M -OX+M-0-M +XOH (X=H or alkyl group) (b)Olation the formation of a hydroxo bridge M-OH +HO- M -+M(OH),M (X =H or alkyl group) Metal-oxo based oligomers and polymers capped by residual hydroxo and alkoxy groups are the result of these two equilibrated reactions.The structure and morphology of the resulting metal-oxo macromolecular networks are dependent on the respective J. Muter. Chem. 1996 6(4) 511-525 rates of the different reactions Rearrangement reactions then occur leading preferentially to weakly branched polymers When these structures reach macroscopic size a gel in which solvent and free polymer are entrapped is obtained The gel state is not the only possibility Other final forms such as colloidal solutions or precipitates can be obtained.The forma- tion of gels or colloidal species reflects different growing processes and different polymer-solvent interactions Control of the nature of the intermediate species through the reaction conditions is essential to tailor the final structures. The reactiv- ity of the metal alkoxide' (nature of M and R) the hydrolysis ratio (H,O M) the solvent the reaction temperature the use of complexing agents or catalysts are the main parameters used to achieve control over the size and morphology of the resulting materials Starting from molecular precursors more and more condensed species are obtained leading to colloidal 'sols' and then to 'gels' A 'xerogel' can be made upon drying the gel under ambient conditions Evidently the possibility of obtaining solutions with controllable viscosity is of funda- mental interest to process these materials' as thin films (spin or dip coating techniques) fibres powders monoliths or particles of various sizes and shapes The chemical reactivity of the metal alkoxide in the hydro- lysis step is determined by both the nature of the metal M and the steric hindrance of the alkoxy groups *.The major parameters'' appear to be the electrophilic character of the metal atom (measured by electronegativity x) and its ability to increase its coordination number N. The unsaturation degree of the metal coordination can be simply expressed by the difference N-2 where N is the coordination number usually found in the oxide and is the oxidation state.Table reports these values for different tetravalent metal alkoxides The difference of reactivity between silicon alkoxides and other transition-metal (TM) alkoxides is demonstrated by the vari- ation of the (N-Z) value. The following sequence of reactivity is usually found Si(OR) <<<Sn(OR) =Ti(OR) < Zr(OR) = Ce(OR) Silicon alkoxides are not very reactive (low electro- philicity N -2= 0). The gelation therefore takes several weeks when neutral water is added and the reaction rate must be increased by using catalysts. The reaction rate depends strongly upon the catalysts (acidic basic or nucleophilic) Molecular precursors R',Si(OR),- ,(R' = alkyl phenyl H etc ) are also used to produce hybrid materials of class 11 their chemistry will be detailed later.Transition-metal alkoxides (Sn Ti Zr etc ) are generally very reactive* and their hydrolysis leads immediately to the precipitation of the 0x0 polymers The reactivity must be controlled by using chemical additives l2 Inorganic acids13 have been described as inhibitors but strong complexing ligands (polyhydroxylated ligands organic acids P-hydroxyacids /I-diketones and allied derivatives) are much Table Properties of some tetravalent metal isopropoxides (2= 4) x" Nh N-2' Si(OPr') 100 Sn(0Pr' ) Ti(OPr') Zr(OPr') Ce (OPr' ) " = electronegativity N =coordination number of the metal atom N -2 =degree of unsaturation. Fig. TM alkoxide complexation by P-acetylacetonates derivatives 512 J Mater Chem 1996 6(4),511-525 more efficient' for controlling the reactivity of TM alkoxides (Fig 1) Chelating agents react with TM alkoxides in the following manner.M(OR) + xHacac -+ M (OR) -Jacac) + xROH For M = Ce Ti Zr etc the strong decrease of reactivity from the pure alkoxide to the modified alkoxide M(OR),-,(acac) is proven lo l2 l4. Turbid or transparent gels are obtained for low modification ratios stable sols or molecular clusters are obtained for higher modification ratios l5 From an extensive study of the phase diagram it becomes evident that the acac groups are not fully removed from the metallic centres even for high hydrolysis ratios. These groups are still present in the final materials or at the surface of the clusters Such complexing ligands can be used to protect the surface of nanosized particles and prevent their aggregation l6.The use of functionalized complexing ligands is important in the synthesis of class IT materials and will be extensively described later Hybrid materials are made by mixing organic and inorganic components Control of the properties of the final material is achieved by controlling the chemical nature of the organic and inorganic phases the size and morphology of these domains (nm to sub-pm scale) and the nature of the interphase inter- action. The first step in the procedure is obviously to find some common suitable solvents and compatible reactants. To illustrate different approaches described in the literature some representative examples for synthesizing hybrid materials are presented Hybrid organic-inorganic materials class I In class I materials organic and inorganic components are linked together through weak bonds (van der Waals ionic or hydrogen bonds hydrophobic-hydrophihc balance).They result from much research work emerging from sol-gel and polymer chemists and these materials will present a large diversity in their structures and final properties Organic dyes embedded in sol-gel matrices. Small organic molecules entrapped in an inorganic network is certainly the most simple representation of a hybrid material It corresponds to the doping of sol-gel matrices by organic dyes inorganic ions or molecules resulting in fluorescence photochromic or non-linear optical (NLO)properties l7 Organic molecules such as rhodamines pyranines coumarins porphyrins phthalocy- anines and spiropyrans as NLO dyes have been entrapped in inorganic networks such as silica aluminosilicate or transition- metal oxide based gels (ZrO T10,) (Fig 2).The choice of the composition of the inorganic matrix is an elegant way to change the refractive index and to modulate the mechanical properties of the final materials Basically the inorganic mol- ecular precursor (alkoxide) the dye and the catalyst are mixed in a common solvent Water is then added to the mixture to begin the polycondensation and the dye molecules are uni- formly trapped in the growing polymer Another alternative is to dip an inorganic xerogel into the dye solution Capillarity could lead to a homogeneous distribution of the dye entities In fact weak interactions between the dye and the inorganic matrix (hydrogen bonds van der Waals forces etc) account for the dispersion of the dye within the structure," and the final properties of the materials (photoresponse reversibility stability etc ) Organic monomers embedded in sol-gel matrices.oSol-gel inorganic matrices are often very porous structures ( A < pore size< nm). The pores of the structure may be filled with molecules by immersing the bulk in a solution containing polymerizable organic monomer (methylmethacrylate buta- diene and derivatives etc ) and a catalyst 2o In a second step organic polymerization is started either by UV irradiation or by heating and the polymer (PMMA PBu etc) is formed (Fig 3).Transparent monoliths of large size with a tunable key to symbols used in all figures:-alkoxide alkoxide Inorganic precursor functionalbed by a inorganic cluster ,$J functionalized by labile '(alkoxide molecule) non-labile polymerizable polymerizable group groups bis(organical1y & bis( silicon end- organic molecule organic molecule modified)silicon A w (dye ...) ((surfactanle ...) alkoxide J organic monomer &% organic monomer polymer chain polymer chain Fig. Organic dyes embedded in sol-gel matrices and key to the symbols used in the figures hv -or heating Fig. Organic monomers embedded in sol-gel matrices followed by polymerization refractive index can be obtained for optical applications depending on the size and geometry of the holes the difference in the refractive index between the two phases and the organic inorganic ratios.An obvious problem is related to the difference of density between the monomer and the polymer leading to strong mechanical stresses in the materials and the formation of many optical defects. Organic functional mole- cules can be also mixed with an organic monomer. Perylene dyes and also enzymes and porphyrins have been incorporated into these hybrid materials leading to sensors or fluorescent silica microspheres composites with lasing proper tie^."^ Inorganic particles embedded in a polymer. For a long time the mechanical properties of polymeric blends have been adjusted by incorporating inorganic fillers (Fig.4). The conven- tional process is to mix together the polymer (or a prepolymer) and the inorganic particles. Nonetheless the high viscosity of the mixture leads to the agglomeration of particles. The resulting inhomogeneity within the materials decreases the polymer-filler interactions. Using a suitable solvent could prevent the lack of homogeneity but further drying steps must be planned. These techniques are also used to prepare multi- component ceramic pastes which can be cast in rno~lds.~ Powders of MgO A1,0 and SiO are mixed with a water- soluble polymer and the viscosity of the gel is adjusted by changing the concentration of the solute. Ceramic hodies of cordierite ( Mg2A1,Si,0,,) are then obtained after firing.Obviously this process is easy and fast but the chemical homogeneity required to obtain complex ceramics (cordierite mullite YBaCuO etc.) is difficult to achieve. Polymers filled with in situ generated inorganic particles. A possibility to overcome the inhomogeneity of materials obtained by embeddment of inorganic particles in polymers (see previous section) is to build the inorganic clusters inside the polymeric structure (Fig. 5)." A typical method consists of mixing together the polymer and the metal alkoxide in a suitable solvent (alcohol or THF). In a second step catalyst and water are added to the mixture and the polycondensation is performed in situ. The best homogeneity is achieved when the weak interactions developed between both phases are sufficient to force both networks to interpenetrate mutually at J.Mater. Chem. 1996. 6(4) 511-525 -stirring Fig. Inorganic particles dissolved in gels or polymers & H2° -catalyst Fig. Polymers filled with in situ grown organic particles the molecular level. The sol-gel process is therefore generating hydroxy groups M-OH; some of those could remain on the surface of the growing 0x0-polymers exhibiting Brarnsted acidity. Carbonyl groups are present in many organic polymers (such as polyamides) and are well known as strong acceptors of acidic hydrogen to form hydrogen bonds. Silica nanocom- posites have therefore been obtained with polymers such as poly (2-methyl 2-0xazoline),~~ poly (N-vinyl pyrrolidone)22 or p~ly(N,N-dimethylacrylamide).~~These materials have good optical properties which can be modulated by the silica or- ganic ratio. The presence of hydrogen bonding between the two phases has been confirmed by 13C NMR and IR spectros~opies.~~~~~ Simultaneous formation of interpenetrating organic-inorganic networks.The design and preparation of monolithic composite materials with good optical properties is a challenge. The homogeneity of the materials the size and shape of the nanodomains must be controlled. A major problem is the shrinkage of the materials during the evaporation of the solvent.24 Generally sol-gel processes are performed in dilute solutions (alcohol THF excess water etc.) and a large amount of solvent must be removed after the formation of the network.Furthermore the change of solvent composition during the process causes phase demixing and inhomogeneity of the composite. Alternative routes to avoid these problems have recently been proposed for the production of homogeneous nanocomposites based on silica with minimal shrinkage a wide choice of polymer structure and a huge range of silica-polymer compositions. The use of modified silicon alkoxides as starting units has been pr~posed~~,~~ (Fig. 6). These alkoxide molecules possess two distinct reactivities the first is due to the metal atom and causes the formation of the oxide network SiO through the condensation mechanism and the second results from the polymerizable group.Cyclic alkenols are polymerized via ring-opening metathesis polymerization initiated by a redox catalyst (Ru3+ salts) whereas alkoxy 514 J. Muter. Chem. 1996 6(4) 511-525 groups carrying methacrylate functions are polymerized by a free-radical mechanism initiated by either UV-light or heating in the presence of a catalyst. The functionalized alkoxy group is initially bonded to the metal atom oiu an M-OC bond. This bond is hydrolysed during the hydrolysis-condensation step thus releasing the polymerizable organic groups. Two networks are then formed independently without mutual chemical bonds. No solvents are released during the reactions and if the density of the monomeric species and the polymer are similar the shrinkage will be negligible.This process can lead to monolithic pieces of large size and with good optical properties. Two interpenetrating networks can be obtained by adjusting the relative kinetics of organic and inorganic reac- tions. The organic reaction must be controlled by the choice of the initiator its concentration with the use of an efficient nucleophilic catalyst (such as NaF) which leads to a fast silica polyc~ndensation.~~ Obtention of ordered organic-inorganic structures. The obten- tion of ordered structures has certainly been one of the outstand- ing goals for materials scientists during recent years. More and more physical concepts are dealing with the anisotropic proper- ties of the material and technological realizations for such advanced materials are expected in the fields of 1D and 2D conductivities membranes anisotropic optical properties non- linear optics etc.Several approaches to the production of such structures have already been described. The first method con- cerns the insertion of organic molecules or polymers into an anisotropic inorganic network [Fig. 7(u)]. The insertion reac- tions of organic molecules have been extensively described in host structures such as clays silicates metal phosphates and phosphonates metal oxide halides chalcogenides etc.28 An interesting inorganic matrix is the vanadium pentoxide (V205) gels. They are obtained through sol-gel processes by acidifi- cation of metavanadate or hydrolysis-condensation of vanadium oxo-alkoxides.29~30 Tactoidal gels of formula V2O5.nH2Oare then obtained.They are composed of negatively methylmethacryl derivative Si02 SiO cycloalkenol derivative H20 + heat or hv -NaF + R?or R" Q Fig. Simultaneous formation of interpenetrated organic and inorganic networks charged flat ribbons. Films exhibiting a layered structure are obtained when the sol is deposited on a glass substrate. The redox properties of the vanadium oxide gels their mixed electronic-ionic conductivity properties and the incorporation of organic molecules inside these structures have been widely studied.29 Insertion of organic molecules is obtained by dipping the inorganic materials into a solution containing the organic component. The driving forces for the insertion process may involve redox reactions acid-base chemistry solvent or ion exchange.Molecules such as alcohols alkylamines metallocen- ium ions viologens and sulf~xides~~~~~ have also been inserted into the host structure. Moreover the structural analysis of the final materials shows that inserted molecules are oriented along specific directions in the interlayer space. The preferred direction results from a competition between van der Waals and hydrogen bonding steric hindrance electrostatic repulsions and lattice energy; upon that depends the nature of the guest molecules. Vanadium pentoxide gels can also intercalate polymers such as poly(ethy1ene oxide) or poly(viny1 pyrr~lidone).~~ Polymeric chains are intercalated between the oxide sheet and the stacking of the layered structure is preserved.Another alternative is to insert the monomers first and then to promote their polymenz- J. Muter. Chem. 1996 6(4) 511-525 soaking+ A W AA AA AVA Fig. Ordered structures obtained by (a) insertion reactions and (b)anisotropic inorganic structure building ation in sit^^^ (oxidative polymerization of aniline pyrrole and thiophene derivatives). Recently electronically conductive poly- mer nanostructures [polypyrrole poly( 3-methylthiophene) or polyaniline] have been obtained by oxidative polymerization of the corresponding monomers entrapped in a template nano- tubular alumina matrix.35 Fibrils with diameters ranging from 20 to nm are obtained.A strong increase of conductivity is measured for the thinner fibres. This effect is related to the stronger anisotropy and molecular organization of the polymer. Strong interactions between the host template structure and the guest molecules account for this effect which may be enhanced by modifying the nature of the surface (grafting of organically modified silanes on the pore walls). A different approach is to build anisotropic inorganic par- ticles using organic molecules and self-assembled aggregates as structure-directing agents [Fig. 7(b)]. Hollow silica cylinders of sub-pm diameter are obtained by depositing silica onto phospholipid Silicate-surfactant mesophases have been obtained by mixing tetraethoxysilane (TEOS) and basic aqueous solutions of surfactants such as cetyltrimethylammon- ium hydroxide (CTAOH) and cetyltrimethylammonium bromide (CTAB).37 Depending on the respective ratios the surfactant-inorganic hybrids exhibit cubic hexagonal or lamellar structures. The cooperative organization between the inorganic species and the surfactants have been studied by 'H NMR spectroscopy X-ray scattering and electron microscopy which have demonstrated the strong anisotropy of these new com- posite materials.Similar experiments have been performed on (a1umino)silicates and the calcination of the mesophases leads to mesoporous zeolites and oxide ceramics. Lyotropic liquid crystals and quaternary ammonium surfactants have also been used as promising tools in tailoring the porous structure of inorganic gels and their textural ~rdering.~' 516 J.Muter. Chem. 1996 6(4) 511-525 Hybrid organic-inorganic materials class I1 Class I1 materials are hybrid structures in which organic and inorganic components are grafted together through strong covalent or iono-covalent chemical bonds. The molecules used as starting building blocks for class I1 hybrids possess at least two distinct functionalities alkoxy groups ( R-OM bonds) which should experience hydrolysis-condensation reactions in the presence of water and lead to an 0x0-polymer framework and metal-to-carbon links which are stable in the hydrolysis reactions. The nature of the stable metal-to-carbon link depends on the nature of the metallic cation.Organometallic links (M-C bonds) are stable towards hydrolysis when M is silicon tin mercury lead or phosphorus. On the contrary M-C bonds are not stable when M is a transition-metal cation. Those M-0-C bonds which are stable upon hydroly- sis could be the links between the organic and inorganic parts. Complexation by polyhydroxylated ligands organic acids. p-hydroxyacids p-diketones and allied derivatives are also u~ed.~.'~ Hybrids obtained from organically modified silicon alkoxides. The chemistry of organic silicon derivatives is well developed. The synthesis and properties of molecules with formula Si(OR),-xR,(x=l or 2) with non-labile Si-R' groups (R'= alkyl aromatic substituent etc.) and hydrolysable Si- OR bonds have been widely described and many of these molecules are also commercially available.If the R' group bears a reactive function (vinyl amines isocyanates etc.),then organic chemis- try could be easily performed on this branch. Two methods have been developed for the synthesis of silicon oxide based hybrid materials. Sequential synthesis. In this method both networks are obtained sequentially in a two-step reactions (Fig. 8). Firstly the inorganic network is created by the polycondensation of the silicon alkoxide which leads to the formation of an oxo- polymer surrounded by organic groups. In the second step an organic reaction is performed with the organic radical. Organic polymerizations of methylmethacryl vinyl ally1 and epoxy R‘ groups have been extensively studied and described.They lead to hybrid materials where both components are network former^.^.',^^^. The choice of reaction conditions for the two successive reactions as well as the possibility to vary the 0rganic:inorganic ratio (adding TEOS or monomer molecules) allows materials with a wide range of properties to be obtained. These materials are usually called ORMOSILs (organically modified silanes) or ORMOCERs (organically modified cer- amic~),~~and they possess great potential because the polymer brings new properties to the inorganic netw~rk~~.~.~~ (flexibility hydrophobicity refractive index modification etc.). The choice of an organic group R’ which is no longer reactive has also been investigated.These network modifiers (Si-CH,. Si-C,Hj etc.) are studied extensively for surface modification of films or particles in the fields of corrosion protection surface treatment membranes and chromatography. R’ groups with a special functionality (dye,40 crown ether,41 persistent radi~al,~’ etc.) are also widely studied. NLO-ph~re,~~ A better stability to leakage than class I materials is expected. The mixing with dialkoxysilanes R’R”Si(OR) has also been studied.44 Poljfunctional alkoxysilanes. Polyfunctional alkoxysilanes are organic units (R’) to which two or more %(OR) groups are bonded through Si-C bonds. When two trialkoxysilane groups are bonded to the R’ unit the generic formula is ( R0)3Si- R’- %(OR),. The trialkoxy groups must be further condensed in the presence of water-catalyst mixtures to obtain hybrid materials (Fig.9). Molecular or macromolecular organic units R’ are described in the literat~re.~~.~~ For molecular units precursors with many different geo- metries (aryl rigid rod spacers acyclic flexible spacers) are used to control precisely the parameters that govern the structures of the final materials.46347 The hydrolysis condensation of all these precursors leads to microporous materials with surface area from less than m2 g-’ up to m2 g-’ depending on both the nature of the precursor and the nature of the catalyst or the solvent. Removing these organics by calcination or plasma gives interesting materials in the field of nanomembranes.Alkoxjsilanes functionalized by polymers. Many studies are devoted to the use of polymer based polyfunctional alkoxy silanes in order to get hybrid organic-inorganic polymeric network^.'^,^^ Pioneering works dealt with materials obtained by coreaction of metallo-organic precursors (such as silicon or titanium) and natural polymers such as polysa~charides,~~ catalyst (HCI or NaOH or NH4F) cellulosic materials or vegetable oil derivatives. These func- tional polymers have hydroxy groups which could react with the metal-oxo polymers which are formed in situ. These cross- linkers are used to control the viscosity of the solution and enable better processing. Recently reactive alkoxysilane groups [-,%(OR),] have been grafted to many kinds of oligomers and polymers (Fig.Many chemistry pathways have been explored to produce such silicon end-capped precursors such processes include direct synthesis through organometallic methods or the coupling of a reactive macromer with a reactive trialkoxysil- ane (e.g. R‘ =isocyanate amine carboxy alkyl halide etc.). Some of the processes are illustrated in Table 2. These hybrids are very interesting because of the wide range of properties which can be achieved.” The final features of the hybrid depend on the properties of the organic polymer the degree of phase dispersion and the homogeneity at thenm scale.9d. They depend on the precursors and the hydrolysis- condensation reactions including the chemical nature and the molecular mass of the functionalized macromers the density of reactive Si(OR) groups the solvent the hydrolysis ratio and the nature of the catalyst.Highly functionalized high-technology polymeric materials are then finally obtained. They present interesting thermal mechanical optical and ionic properties. The choice of the starting materials is strongly influenced by polymer science. Hybrids based on transition-metal oxide (TMO) networks. The strong reactivity of the transition-metal-carbon bond towards hydrolysis is well known but the chemical modifi- cation reactions of TM alkoxides have been developed to overcome this problem. Grafting a silica layer on the TIMO.~~The first and \implest approach to graft organics to TMO is to use an intermediate silica layer (Fig.11). The surfaces of TM-0x0 polymers or colloids have a high density of hydroxy groups hl-OH which can react with silicon alkoxides or organically modified silicon alkoxides thus creating M-0-Si bonds. This process is used to bond vinyl epoxy or methacryl modified silane to zirconia or titania. Afterwards this organic layer can react with organic monomers and forms an organic layer around the metal-oxo polymer. A one-pot procedure is aed to treat dialkyl siloxane R’Si(OR)2 with titanium alkoxitle in an acidic rnedi~m.~’ Short linear polydialkylsiloxane chains HO [R’SiO],R or rings are growing simultaneously to form polyoxotitanate-oxo polymer [TiO,(OH),(OR”),-,-,],. When this solution evaporates some of the reactive titania sites react with those of the PDMS units.The two networks are then crosslinked through the formation of Ti -0-Si bonds which can be demonstrated by 29Si and ”0 NMR spectroscopy.58 From the high mixing level of the two phases. transparent coatings are obtained. hv or heat catalyst -(AIBN POB) Fig. Synthesis of hybrid materials from organically modified silicon atoms J. Muter. Chem. 1996 6(4) 511-525 8g H20 -catalyst (HCI or NaOH or NH4F) Y Fig. Synthesis of hybrid materials from polyfunctional alkoxysilanes H20 -catalyst (HCI or NaOH or NH4F) c“4 Fig. Synthesis of hybrid materials from alkoxysilanes functionalized by polymers Table Synthesis of modified silicon precursors“ Synthesis Ref.Comments Si(OEt)4 + HO-R -(EtO)sSi-OR 479 trans-esterifcation Si(OEt)4 + X-R --t (EtOhSi-R X= CI Br ... R = alkyl phenyl ... &ignardreaction (Et0)3Si-H + LR-(EtO)3SiPR hydrosilation (Et0)3SiAN=C=O + HO-R -(EtO)3SiANH-$-O-R acylation0 (low yield) (Et0)3SiAN=C=0 + HzN-R +(EtO)@iANH-$-NH-R acylation 0 acylation in basic -(Et0)3SiANH-$-R (good yield) (Et0)sSiANHz + HoyR media->qO formation 0 ->condensation of SiO (EtO)3siANH-R’ + X a -(EtOI3Si”E;Ia Hofmann synthesis of R‘ x = CI S02CI amines R is a monomer or a polymer; the use of a symmetric R group leads to bis(end-capped) molecules. Complexation of TM alkoxide. The use of complexing ligands ligands. For controlled hydrolysis ratios clusters of defined appears to be a key point for the synthesis of organic-inorganic sizes and structures are synthesized.Their core is formed from structures involving transition metals for which ionic M -C a compact oxide structure while the surface is protected by bonds are easily cleaved by water. In this case strong com- the organic ligands. plexing agents are used (8-diketonates acid derivatives etc.). The synthesis of organic-inorganic structures requires the When these complexes are hydrolysed the alkoxy groups are use of complexing ligands with an organic reactive function removed thus causing the formation of metal-oxo polymers which may be polymerized further (vinyl allyl methacryl etc.). while some of the ligands are still bonded to the metallic. The behaviour of some of these chelates has been studied centre.The strong decrease of the alkoxy reactivity towards recently in titania or zirconia based materials. Generally the hydrolysis is proven and stable sols colloids or gels can be synthesis scheme is similar to those described for silica based obtained while precipitates are obtained without complexing materials (Fig. 8) synthesis of the heterofunctional precursor 518 J. Muter. Chem. 1996 6(4) 511-525 -H20 hv or heat catalyst + catalyst (HCI or NaOH or NH4F) (AIBN POB) Fig. Class I1 hybrid materials anchoring TMO to organics through a silica layer (addition of the polymerizable ligand to the TM alkoxide) controlled hydrolysis to obtain TM oxide clusters or polymers and then organic polymerization of the reacting group in the presence of a catalyst light and finally heat treatment.The stability of carboxylic acid derivatives towards hydrolysis is poor and the organic ligands are more or less removed from the metal atoms during the synthesis steps. The low reactivity of vinyl derivatives or ally1 acetonate grafted to Ti02 systems has been depi~ted.~’ Organic polymerization yields are always very low. Much better results have been obtained with meth- acryl derivatives ligands such as methacrylamido salicylate (MASA) and acetoacetoxy ethyl methacrylate (AAEM) (Fig. 12). These strong chelating ligands are added to the metallic precursor (Zr-alkoxide) with various complexing ratios6’ (AAEM :Zr 0.25-0.75). In a second step both organic and inorganic polymerizations can be managed sequentially or even simultaneously if water and a radical initiator are added to the precursor solution. Milky sols are then obtained.Spectroscopic investigations of the colloids (X-ray absorption HO methacrylamido salicylate (MASA) 0 acetoacetoxy ethyl methacrylate (AAEM) Fig. Complexation agents for TM alkoxides methacrylamido salicylate (MASA) and acetoacetoxy ethylmethacrylate (AAEM) hv or heat n catalyst (AIBN POB) IR NMR) prove that a good yield of organic polymerization is achieved and Zr complexation remains. X-Ray diffraction light scattering and TEM show that branched scatterers are formed. Their structure and texture seems to be mainly gov- erned by the hydrolysis and complexation ratios.Hybrid organic-inorganic polymers are intimately interpenetrated from the nm scale (AAEM :Zr =0.25) to the sub-pm scale (AAEM Zr =0.75).For higher complexation ratios zirconium- 0x0 clusters are connected through long polymethacrylate chains while for lower complexation ratios short organic chains crosslink larger 0x0 particles. Hybrids based on template building blocks. The use of template building blocks as starting units for obtaining hybrid organic-inorganic structures is an approach which is followed by organometallic chemists for various systems (Fig. 13). The synthesis of well defined silicon 0x0-clusters provide some examples. The most studied building blocks are based on cubic functionalized silicic acid clusters61 of formula {[(CH3)2RSi]SSiS020 with R=H (QsMaH) CH=CH2 (Q&”)}.Hydrosilylation reactions are performed to couple these blocks. Tetramethyldisiloxane tetramethylcyclotetrasi-loxane and poly(methylhydrogenosi1oxane) have also been used as reactive spacers in order to produce materials with controlled porosity. The same procedure is followed in order to product. tin-oxo based hybrid species.62 Clusters with the formula [( R’j&(p3-O)14(p2-OH)6](OH)2(HOP?) (R =butyl or buteiiyl) are obtained from the controlled hydrolysis of BuSri(OPr’) . Further organic polymerization of the butenyl derivative in the gresence of AIBN leads to entities with diameters around 60 A proving that the tin-oxo clusters are attached through Fig.Hybrids based on template building blocks J. Mater. Chew. 1996 6(4) 511-525 polybutane chains. In the case of TM-0x0 clusters the M-C bonds are broken in the presence of water. Negatively charged macromolecules based on polyoxometal-lates (POM) have also been ~tudied.6~ The POM entities are organically functionalized through the M-0-Si-C links. [SiWI1O4,J SiR),I4- units carrying two reactive organic groups (R =vinyl allyl methacryl styryl) are further poly- merized in the presence of a radical initiator to yield hybrid polymers in which POMs are linked by polymethacrylate or polystyrene chains. The synthesis of transition-metal-0x0 clusters capped with polymerizable complexing ligands has already been discussed. These clusters may also be linked together when an organic polymerization is initiated leading to an assembly of nano- building blocks.Ordered hybrid materials of class 11. The development of class I1 ordered hybrid materials (Fig. 14) is a challenge for materials chemists in order to provide new materials with improved physical applications. One method used is the building of disordered isotropic structures which may be processed further (poling mechanical deformation etc.) in order to present anisotropic character. Outstanding ordered materials exist near Langmuir-Blodgett films. Oriented films are produced by the self-assembly of molecular units. In the simplest approach trialkoxy (or tri- chloro) silanes [R'Si(OR) where R is a long aliphatic chain with more than ten carbons] react with the surface silanol (Si-OH) groups of the activated silica surface.64 An oriented monolayer of aliphatic chains is formed at the oxide surface and variable compactions and molecular orientations are achieved depending on the experimental conditions.The func- tionalization of the R' group such as the introduction of an alkene a phenoxy or a sulfone group leads to layers with different structures and the possibility of further reactions. The limitation in producing monolayers is overcome by the use of carboxy derivatives such as H,CO2C(CH,),,SiC1 and multi- step self-assembly processes. More than layers can be successively deposited OF a substrate leading to anisotropic layers of more than A in thickness.More complex organic groups such as conjugated aromatic units have also been used to build such multilayer structures. The same idea is developed in building organic-phosphonate hybrids.65 In that case the I+TMO su dace + TMO surface substrate is successively dipped in Zr salt solution and organic phosphonate solution. The building of a self-assembled multi- layer may reach pm thicknesses. Phosphonates functionalized with NL066 or fluorescent dyes,67 poly( phenylvinylene) or polythiophene68 oligomers are being widely studied. Organometallic polymers. Organometallic polymers obtained by grafting functionalized organometallic molecules (such as metallocene derivatives) are also considered at the frontier of hybrid materials.Ferrocene and its derivatives have been grafted to organic or siloxane frameuorks. leading to materials with reversible redox proper tie^.^^ Ferrocene-PMMA copolymers have recently been described as organome- tallic materials with NLO properties and large xz values have been measured." Molecular assemblies of silicon phthalocyan- ine derivatives have also been reported.-' The stacking of elemental planar units leads to polymers possessing redox properties emphasizing the strong electronic interactions between the sites. Some Applications Reaching Applications through the Versatility of the Preparation Process The wide range of synthetic procedures for obtaining organic- inorganic structures leads to the vast range of properties which these materials may possess.Obviously the final materials are not just the sum of the primary components and a large synergy effect is expected from the close coexistence of the two phases through the size-domain effects and the nature of the interfaces. Searching for a material with a given property could then appear as an endless task. Guidelines can be drawn out from the basics of materials and polymer sciences. Generally. the major features of each phase are preserved in the hybrid materials (stability thermal behaviour special properties) and generally only some shifts of the properties of each phase are to be expected. Organic us. inorganic materials properties size effects For centuries the properties of inorganic (metals.ceramics. glasses) and organic (polymers) bulk materials have been investigated with regard to their applications promoting the evolution of civilizations. During the last decades and with "20 catalyst H H H 2O H ___)catalyst H ti *o H H H Fig. Ordered hybrid materials of class I1 (a) monolayers (b)multilayers 520 J. Mater. Chem. 1996 6(4). 511-525 the help of analysis techniques the relationship between the structure and properties of these materials has become clearer Some of these general data are summarized in Table The choice of the polymer is usually guided by its mechanical and thermal behaviour However other properties such as the hydrophobic/hydrophilic balance the chemical stability the biocompatibility the optical (visible and/or IR and/or UV) and/or the electronic properties and chemical functionalities (such as the ones used to solvate molecules or ions) must be considered in the choice of the organic component. The nature of the oxide is determined by the redox properties the density the refractive index.The chemistry of the metal can also guide the chemist in his choice Obviously the nature of the bonds engaged in the organic or inorganic matter are completely different thus explaining the very different behaviour of these two families of materials Another crucial effect is seen when the sizes of the phases change from large bulks to smaller and smaller objects (typi- cally in the nm range). This size effect modulates the properties of nanophased materials,72 some interesting examples of this are (1) thermal behaviour melting points or Tgcan be shifted for tens of degrees or cancelled (2) mechanical properties changes of critical yields or strains (3) rheological and stability of solutions and dispersions the viscosity of polymeric solu- tions is strongly dependent on the molecular mass M,.The stability of colloidal solutions is dependent on the mass of the particles (4)Dynamics of molecules dissolved in liquids filling porous glasses or xerogels rotational diffusion and self- diffusion coefficients decrease markedly when the size of the liquid domain is reduced (5) electronic properties are easily changed by the size of the domains especially when the objects are in thenm range Both inorganic and organic materials exhibit such effects Polyoxometallates are TMO clusters of formula M,O,k-(M=W Mo V 6dnd40).Their structure is based on stacking of MO octahedra and they present redox reversible properties (photochromism electrochromism etc ) The redox potentials and the colours of the redox states can be changed by the number (n) of the metal atoms74 At the two size extremes are the single cation M”+ and the metallic oxide A similar trend is observed in organic conductors where the redox properties of oligomers [poly(viny1idene) or poly- (phenylene)] are adapted by changing the size of the oligo- mers 75. The studies of quantum dots (selenides and sulfides) lead to similar conclusions Optical properties are modulated by the size of the nanoclusters Some similar trends are also observed when measuring the variations of properties from 3D to 2D structures for example studying the properties of a given compound when going from bulk and nanoparticles to surfaces covered by layers There are many effects which account for these size-domain effects.The strongest effect is governed by the surface and interface effects the smaller the particles the higher the devel- oped surface. These surfaces have to be considered as defects of the bulks. The high reactivity of oxide surfaces comes from the high density of hydroxy groups or dangling bonds. They can react further to give strong bonds (through olation oxolation esterification) or weak bonds (hydrogen bonds) with the surrounding medium Molecules near a ‘solid’ surface then experience interface effects as measured from molecular dynamics 7273.The strong hindrance of mobility has been proved by many techniques in porous glasses gels composites (such as by forced Rayleigh scattering by polarized light scattering by NMR or by EPR) and the deactivation of the oxide surface by alkylsilanes decrease has been proven Many studies dealing with the properties of organic dyes embedded in an inorganic matrix imply the same effect. The surface effect can be so strong that the sol-gel matrix prevents the formation of rhodamine dimers Such a result suggests that the dye-dye interactions are weaker than the dye-matrix interactions Rhodamine molecules are absorbed at the surface of the xerogel micropores and high concentrations of dye molecules (up to mol dmP3) can be reached without dimer formation.The interactions of the surface with the dissolved molecules can be checked by controlling the inner surface of the xerogels Such surface effects have been measured in silica based materials doped with photochromic spiropy- ran. The matrix is obtained uza polymerization of Si(OCH,) or EtSi(OCH,) precursors and a ‘reverse photochromic’ effect is observed. This is related to the stronger interactions of the coloured species (zwitterionic form) with the acidic silanol Si-OH groups present at the surface of the inorganic gel through hydrogen bonding The size effect also must be considered.The most trivial way of controlling the size of the nanodomains is to form transparent materials. This requires matching of the refractive index and particles with characteristic sizes in the range of the light wavelength 77. The tremendous effect of the particle size on many physical properties for nanosized objects is measured for electronic conductivities and optical and redox properties Recent theories explain these size effects but only for perfect materials which is certainly far from reality. There again an effect of the size on the quality of the samples and the densities of defects is generally observed. Table Comparison of the propreties of organic and inorganic materials property organics (polymers) inorganics (SiO and TMO) nature of bonds T (glass transition) temperature stability density refractive index covalent [C-C] (+weaker van der Waals or hydrogen bonding) low (-100 to 200°C) low (< “C) 09-1 12-1 ionic [M-01 high (> “C) high (>> 100“C) 0-4 4-2 mechanical properties hydrophobicity permeability electronic properties processabili t y elasticity plasticity rubbery- like (depending on T,) hydrophilic hydrophobic permeable to gases insulating to conducting redox properties high molding casting machining thin films from solution viscosity control hardness strength fragility h ydrophilic low permeability to gases insulating to semiconducting (SiO,/TMO) redox properties (TMO) low for powders needs to be mixed with polymers or dispersed in solutions high for sol-gel materials (similar to polymers).J Muter Chem 1996 6(4),511-525 Tuning the properties by the chemical nature of starting materials Obviously the choice of the starting components is essential to the properties of the materials Such a great deal of work has been devoted to the individual properties of polymers and oxides (silica TMO) that reviewing these features is beyond the scope of this paper. The originality of synthesizing hybrid materials through the sol-gel process offers the possibility of mixing many organic and inorganic precursors to adapt the material properties The mutual role of organic and inorganic components is considered on the basis of their ability to provide individual networks If only one of them develops a structural network the other is considered as a network modifier.The surface modification of oxides gels or glasses by organic-inorganic molecules obviously enters this description Chromatography and derived techniques use derivatization agents with func- tional groups grafted to the silica support Alkanes acids amines chiral groups enzymes liquid-crystal molecules etc are then bonded to achieve effective separations. The formation of ordered organic monolayers on substrates proceeds from the same idea Organic glasses (plexiglass etc) have been protected against scratches by the formation of thin layers of SiO or Zr0279 on the surface Organic and inorganic com- pounds can also be mixed homogeneously in the bulk in order to modify the properties of the materials for example continu- ous changes of porosity and the density and optical properties are measured when variable amounts of (OEt)3SiCH3 are mixed with Si(OEt) in order to form methyl modified silica The tricky choice of the starting components and the need to add more and more precursors can be illustrated by some developments for multifunctional materials (a) increasing the refraction index by adding. TMO to a UV polymerizable silica- methacrylate mixture for integrated (b) adding per- fluoroalkyl chains [03SiCH,CH,(CF2),CF,] to silica or zir- conia to obtain hydrophobic coatings7'.The ratio of CH2CH2(CF2),CF3 groups leads to control of the solvent contact angle which can reach a value for water similar to PTFE ( 105"),798o (c) V,O,/modified silica structures Materials with electronic properties are obtained by mixing DEDMS (diethoxydimethylsilane) and vanadium alkoxide [VO(OAmt),] When hydrolysed in acidic media the thin films are green transparent films are obtained under neutral conditions. These differences are related to the changes in the chemical processes which result in different coordination shells of the V atoms Easily reduced vanadium-oxo species are formed at low pH (five-fold coordination) while vanadium in four-fold coordination is obtained at pH =6 5.The organic- inorganic structural PDMS network stabilizes these different species (d) Contact lens materials". The effect of adding different starting molecules is illustrated in Table4 Such a high-technology material should present good optical proper- ties (refractive index no optical defect) as well as adapted mechanical properties biocompatibility hydrophilicity and O2 permeability) To optimize the properties of these materials more than six different compounds must be added in the right ratios and different parallel or successive reactions must be performed All experimental conditions must be controlled such as the solvents the order of the reactions the catalysts and the bath temperature Evidently producing the required materials is difficult and only detailed knowledge of the different reactions involved can lead to a suitable commercial hybrid organic- inorganic nanocomposite Tuning the properties by the dynamic behaviour Most of the properties of advanced hi-technology materials are strongly related to the chemical nature and structures of the components and obviously to their dynamic behaviour The search for materials with suitable mechanical properties (plasticity elasticity strain yield etc) is governed by the molecular properties and the mobility of the polymeric chains At low temperatures reduced motion of the polymer chains is observed leading to fragility while above q,cooperative movement of the chains with larger amplitude are found to occur this leads to more elastic or rubbery compounds Controlling the glass transition temperature T is of fundamental importance for many functionalized hybrids Striking examples are emerging from the search for materials with NLO properties Initially materials with isotropic properties are synthesized and further processing is needed to achieve anisotropic properties In the first step a film is obtained from a suitable solution by spin or dip coating.The NLO dye can be grafted onto the silica networks or embedded in the matrix. The second step is the poling of the material Usually the material is heated near or above its Tg in order to increase the molecular mobility and a strong electric field is applied (kV cm-'). The Corona effect can align the dipolar dye molecules The material is then cooled down and the dye molecules are trapped with a preferred direction. The choice of a suitable matrix and the grafting of the dye units to the silica network retains the anisotropic properties Hybrid materials with ionic conductivity properties have also been described Lithium salts are first dissolved in a suitable phase an organically modified silica (amines sulfonic acids sulfonamide~)~~ or silica-polymer networks [poly(ethy1-ene glycol) poly(propy1ene glycol) etc ] Transport phen- omena of cations in polymeric structures have been widely studied and demonstrate that reasonable values of the Li' mobility are reached if the surrounding solvating media also experiences a high degree of m~bility,'~ such as those measured in polymers above Tp In PEG-silica structures the dependence of the ionic conductivity (oL1+) on temperature demonstrate polymer-like behaviour in agreement with thermal analysis and the NMR experiments which present a value of Tg in the range -60 to +20°C depending on the exact material composition The high solvating character of PEG has been studied to form PEG-SiO hybrids in which very different kind of entities such as organic dyes and molecules or salts can be dissolved Polyoxometallates ([PW12040]3- [SiW,2040]4-j have already been dissolved in such structures 86.The materials exhibit electrochemical and photochromic properties that have been investigated as supports for optical data storage It appears however that both properties could not be found in the same material. The first requires a high diffusional mobility of the POM clusters87 to increase the electronic transfer rate whereas the second needs to trap the clusters and to avoid any electronic exchange.The choice of the matrix composition and structure leads to a control of the balance favouring one of the properties Recently we investigated the dynamic- structure relationships in PEG-SiO materials55 of class I and class I1. The materials were made by condensation of silica in PEG (class I) or condensation of silica end-capped PEG (class 11) In both cases transparent materials in which small silica clusters are wrapped in the PEG phase are obtained (Fig 15) Longer chain lengths and grafting of the polymer lead to a decrease in Tg A more subtle point is certainly the lack of homogeneity of thermal behaviour in the organic phase (only a part of the PEG phase experiences the glass transition) The dynamic behaviour has been mapped with EPR (nitroxide probes) and NMR (liquid and CP-MAS) experiments which demonstrate a strong hindrance of molecular mobility near the silica surfaces Prospects and Conclusion Because of the huge versatility of the synthetic processes and the nearly infinite choice of possible combinations organic- 522 J Mater Chem 1996 6(4) 511-525 added molecule properties of the layers enhancement of properties OR RO-$i-OR OR“3 RO -Si OR Si(OR)4 or/and Ti(OR)4 0 RO-Yr-0 + MMA9 OR Replacing MMA by HEMA 02permeability ; but hydrophobic.02permeability ; but OH is lost upon condensation hydrophilicity too. 02permeability and hydrophilicity ; but porous materials with poor mechanical properties.02permeability and hydrophilicity denser materials ; but brittle materials not machinable. 02 permeability and hydrophilicity denser materials reduced brittleness increased flexibility machinable ; but low wettabilitv. 02 permeability and hydrophilicity denser materials reduced brittleness increased flexibility machinable wettable scratch resistant. Fig. Idealized structures of class I and class I1 nanocomposites SO,-PEG inorganic nanocomposites could form a broad range of advanced materials.88 Some outstanding issues of hybrids must be explored at the frontiers of science technology and knowl- edge. During early studies the cooking of complex mixtures led to materials with unexpected features; many applications of these new sophisticated materials have been described.After these initial studies a more critical point of view has been adopted and more systematic studies were carried out. A wide investigation of these materials began with the help of most of the available techniques (such as water titration elementary analysis chromatography rheology light and X-ray scattering X-ray diffraction optical techniques) and spectroscopies (such as IR UV-VIS fluorescence electrochemistry mass spec-trometry multinuclear liquid and solid-state NMR X-ray spectroscopies XANES and EXAFS EPR). They demonstrated that both structural and ‘smart’ hybrid materials may be achieved in the near future. These trends are supported by the research works published during the last few.The following examples are major fields of investigation. ( 1). The search for materials with suitable mechanical properties. This is one of the foremost areas for hybrid materials and these studies are guided by the strong similarities which could be found with structural composite^.^^. The effect of mixing and/or grafting polymers to glass fibres or woven fabrics to reinforce their structures is a current issue. When the size of both phases is reduced from the pm scale down to thenm range strong modifications of the properties is expected. The effect of changing the polymers the inorganic phase the size and shape of the domains is under investigation. The study of smart hi-technology materials with useful mechan- ical properties is beginning by mimicking the recent investi- gations of polymer science.These compounds must respond to external stimuli such as solvent composition pH light electric field or temperature. Some examples arise from photo- active polymers B9 (reversible change of size under illumination) or hydrogels (abrupt swelling to a critical point accompanied by strong changes of mechanical moduli). (2) Coating materials and membranes are very active research. The goal of these materials are evidently opposite but both deal with the control of liquid and gas diffusions. The control of porosity (active surface area size of cavities) and interactions with solvents and molecules ( hydrophobic-hydrophilic balance) are the key points of these properties.Large porosity characterizes membranes and many attempts to use polyfunctional alkoxysilanes (RO),Si-R’-Si(OR) show very promising results. The pos- sibility of enhancing selective transport inside the membranes by specific carrier groups (ligands with specific interaction crown ethers cryptands etc.) is very attractive. In contrast barrier layers and anti-scratch hard coatings have been devel- oped to protect or improve polymers or glasses. The control of the refractive index of these coatings by adding TMO particules has been developed for optical fibres and light waveguide^.^' Corrosion-inhibiting coatings for metal surfaces J. Muter. Chern. 1996,6(4) 511-525 and hydrophilic protective coatings (anti-fogging) are being studied.The presence of organic entities leads to a low porosity while the inorganics are essential for the grafting of the protective layer to the surface (3) Optics was certainly one of the first applications of hybrid materials 17b. The doping of materials with dyes fluo-rescent dyes photochromic dyes or NLO dyes etc is a very active field of research and good results are often reported Up-to-date technologies have a great need for materials with advanced properties. They may be produced from hybrids photochromic hybrid layers for optical data storage with high spatial resolution optical waveguides couplers gratings and lenses for microoptical applications stable NLO materials and devices powders doped with sensitive fluorescent molecules for sensors or gel-glass dispersed liquid crystals for electro- (nematic phases entrapped in modified silica network) etc.The study of electrochromics for smart windows has also found some success using hybrid materials. The electroactive layers and the electrolytic properties can be both modulated Most of these materials must be deposited as layers of variable thicknesses on various substrates Control of the viscosity of the solution gives a noticeable versatility to the process. The possibility of forming ordered structures must be further studied because structures with anisotropic optical properties are key materials (refractive index NLO fluorescence etc ) (4) More and more compounds presenting electronic properties are also under study Redox targets have been entrapped in hybrid matrices leading to photo- or electro- active materialsg1.These properties have also been used to study the change of structure during the sol-gel transition via the determination of self-diffusion coefficients 94. These proper- ties are also expected for redox sensors and biosensors Because of the flexibility of the chemistry the redox properties of materials can be tuned Examples arise from V,O,-DEDMS and POM-Si0,-PEG systems Very promising results arise from electronic conductors such as silica-polypyrrole silica- aniline interpenetrated networks and V,O,-polypyrrole lay-ered structures. The search for anisotropic conductivity proper- ties is clearly evidenced by this last example Recently semiconductor research has also found interesting isolating materials that can be used in organic transistors and chips95 Self-assembled monolayers of alkyltrichlorosilanes exhibit a resistivity similar to a polymer layer of nm (5) Evidently hybrid structures provide a lot of opportunity for biomaterials Mother Nature designed a lot of these archi- tectures and evidently chemists aspire to improve them!.This field covers many very different investigations. The synthesis of new composite micr~structures~~ and biomimetic assem-opens the area of ordered and anisotropic networks A variety of shapes and compositions have been elaborated from mixtures of lipids and iron while silicate-surfactant mesophases are under development 98.They are also potentially useful for mimicking biogenic structures and the growth of minerals in living cells and bodies. This approach provides new tools for understanding the interactions and reactivities of molecules in confined media which can be used in the field of catalysis A different use of hybrid materials has been described with biosensors and biomolecular materials in which proteins are encap~ulated~~ with regard to the delicate nature of proteins and enzymes (narrow pH range) intricate con-ditions for the material synthesis are required A change of colour of protein doped compounds is observed when changing the medium demonstrating the porosity of the materials and the sensitivity of the units Good yields of enzymatic activity (oxalate oxidase glucose oxidase etc ) and biocatalysis by lipases'" have been measured in transparent hybnd compounds Only a few properties and potential applications of hybrid materials have been described in this paper An exhaustive list of compounds would need a much bigger volume Furthermore 524 J Muter Chem 1996 6(4) 511-525 the quick expansion of this young field of research prevents such a possibility where many papers are published every month Development of the hybrids always demands more and more chemists to build these structures more and more physicists to exploit their potentialities.Their complexity is a challenge both for most of the up-to-date analyses techniques and for the attempt to use theoretical models to forecast the properties of new compounds Obviously the study of hybrid organic-inorganic materials requires the association of scientists from many disciplines The major potential of these materials is certainly in producing more and more ordered and anisotropic structures.The control of the specific interactions between both phases is a key in this direction It should also promote better homogeneity and better properties of these materials in the future References [In regard to the immense number of papers in each field only the most representative papers for each theme are cited in this bibliography 1-_-1 Better Ceramics. Through Chemistry VI eds A K Cheetham C J Brinker M L Mecartney and C Sanchez Muter Res Soc Svmp Proc ,1994,346 2 Seventh International Workshop on Glasses and Ceramics from Gels Special issue of J Sol Gel Sci Tech 1994,2 3 Proceedings of the First European Workshop on Hybrid Organic Inorganic Materials (Synthesis Properties Applications) eds C Sanchez and F Ribot Bierville-France 4 (a) Hybrid Organic-Inorganic Materials ed C Sanchez and F Ribot Special issue of New J Chem 1994 18 (b) Hybrid Organic-fnorganic Materials ed L L Klein and C Sanchez Special Issue of J Sol-Gel Sci Tech 1995 5 U Schubert N Husing and A Lorenz Chem Mater ,1995,5 5 C Sanchez and F Ribot New J Chem 1994,18,1007 6 C J Brinker and G Scherrer in Sol-Gel Science,.The Physics und Chemistry of Sol-Gel Processing Academic Press San Diego 1989 7 J Livage M Henry and C Sanchez Prog Solid State Chem 1988,18,259 8 D C Bradley R C Mehrotra and D P Gaur in Metal Alkoxides Academic Press London 9 (a) Sol-Gel technology for thin films fiber preforms electronics and especialty shapes ed L C Klein Noyes Park Ridge NJ 1988 (b)H Schmidt in Chemistry Spectroscopy and Applications of Sol Gel Glasses ed R Reisfeld and C K Jmgensen Springer- Verlag Berlin 1991 (c) H Schmidt in Ultrastructure Processing of Advanced Materials ed D R Uhlmann and D R Ulrich Wiley New York 1992 ch 38 (d) H Schmidt in Chemical Processing of Advanced Materials ed L L Hench and J K West Wiley New York 1992 ch 10 C Sanchez F Ribot and S Doeuff in Inorganic and Organometcillrc Polymers with Special Properties ed R M Laine NATO AS1 series 1992,206,257 11 R K Iler in The Chemistry ofSrlica Wiley New York 1979.12 C Sanchez J Livage M Henry and F Babonneau J Non-Cryst Solids 1988 100 13 B E Yoldas J Muter Sci ,1986,21,1086 14 R C Mehrotra R Bohra and D P Gaur in Metal b-diketonates and Allied Derivatives Academic Press London 15 (a) C Sanchez M In P Toledano and P Griesmar Muter Res Soc Symp Proc 1992 271 669 (b) F Ribot P Toledano and C Sanchez Chem Mater ,1991,3,759 16 M Chatry M In M Henry C Sanchez and J Livage J Sol-Gel Sci Tech 1994,1,233 17 (a)R Reisfeld and Ch K Jsrgensen in Chemistry Spectroscopy and Applications of Sol-Gel Glasses ed R Reisfeld and C K Jsrgensen Springer-Verlag Berlin 1 p 207 (b) Sol-Gel Optics ed J D MacKenzie and D R Ulrich Proc SPIE 1990 1328,1992,1758,1994,2288 18 D Levy S Einhorn and D Avnir J Non-Cryst Solids 1989 113,137 19 M Canva P Georges A Brun F Chaput F Devreux and J P Boilot in Sol-Gel Optics ZI,ed J D Mackenzie Proc SPIE Washington 1758 20 (a) R Reisfeld D Brusilovsky M Eyal E Miron Z Burshtein and J Ivri Chem Phys Lett 1989 160 43 (b) E J A Pope A Asami and J D Mackenzie J Muter Res 1989,4,1018.(a) T Saegusa and Y Chujo Polym Prep 1989 1 39 (b) A Morikawa Y Iyoku M Kakimoto and Y Imai J Muter Chem 1992,2,679 M Toki T Y Chow T Ohnaka H Samura and T Saegusa Polym Bull 1992,29,653 S Kure H Matsuki R Jordan Y Chujo and T Saegusa Polym Prep Jpn 1990,39,1684 B M Novak Ado Muter 1993,5,422 B M Novak and C Davies Macromolecules 1991,24,5481 M W Ellesworth and B M Novak Chem Mater 1993,5,839 (a) R J P Corriu D Leclercq A Vioux M Pauthe and J Phalippou in Ultrastructure Processing of Advanced Ceramics ed J D Mackenzie and D R Ulrich Wiley New York 1988 113 (h) R J P Corriu C Guerin and J E E Moreau Top Stereochem 1984,43 (a) D O’Hare in inorganic Materials ed D W Bruce and D O’Hare Wiley Chichester 1992 p 165 (b)E Ruiz-Hitchky Adc Muter 1993,5 J Livage Chem Muter 1991,3 M Nabavi C Sanchez and J Livage Eur J Solid State inorg Chem 1991,28,1173 (a) P Aldebert N Baffier N Gharbi and J Livage Muter Res Bull 1981,16,669 (b)A Bouhaouss and P Aldebert Mater Res Bull 1983,18,2247 B Casal E Ruiz-Hitzky M Crespin D Tinet and J C Galvan J Chem Soc ,Faraday Trans 1989,85,4167 Y J Liu D C Degroot J L Schindler C R Kannewurf and M G Kanatzidis Adv Muter 1993,5 (a)M G Kanatzidis and C G Wu J Am Chem Soc 1989 111 4139 (h)M G Kanatzidis C G Wu H Marcy D C Degroot and C R Kannewurf Chem Muter 1990,2,22 C R Martin Acc Chem Res 1995,28,61 S Baral and P Schoen Chem Mater ,1993,5,145 A Firouzi D Kumar L M Bull T Besier P Sieger Q Huo S A Walker J A Zasadzinski C Ghnka J Nicol D Margolese G D Stucky and B F Chmelka Science 1995,267,1138 T Ddbadie A Ayral C Guizard L Cot J C Robert and Poncelet Muter Res Soc Symp Proc 1994,346 I Gautier Luneau A Mosset J Galy and H Schmidt J Muter Scz ,1990,89,3739 65 73 81 C Sanchez J Livage M Henry and F Babonneau J Non-Cryst Solids 1988 100 C Sanchez and M In J Non-Cryst Solids 1992,1471148 D Hoebbel K Endres T Reinert and H Schmidt Muter Res Soc Symp Proc 1994,346,863 F Ribot F Banse and C Sanchez Muter Res Soc Symp Proc 1994,346,121 P Judeinstein Chem Muter 1992,4,4 A Ulman Adv Mater 1990,2,573 Guang Cao Hin-Gi Hong and T E Mallouk Ace Chem Res 1992,25,420 (a)H E Katz W L Wilson and G Scheller J Am Chem SOL 1994,116,6636 (b)N J Long Angew Chem ,Int Ed Engl 1995 34,21 K Motesharei and D C Myles J Am Chem Soc 1994 116 H E Katz S F Bent W L Wilson M L Schilling and S B Ungashe J Am Chem Soc 1994,116,6631 T Inagaki H S Lee,T A SkotheimandY Okamoto,J Chem Soc Chem Commun 1989,1181 M E Wright E G Toplikar R F Kubin and M D Seltzer Macromolecules 1992,25 D C Gale and J D Gaudiello J Am Chew SOC 1991,113,1610 Molecular Dynamics in Restricted Geometries ed J Klafter and J M Drake Wiley New York J M Drake and J Klafter Phys Today May 1990 p M T Pope and A Muller Angew Chem Int Ed Engl 1991 30,34 R Schenk H Gregorius K Meerholz J Heinze and K Mullen J Am Chem Soc 1991,113,2634 D Avnir D Levy and R Reisfeld J Phys Chem 1984,88,5956 H Krug and H Schmidt New J Chem 1994,18 J Pesek and T Cash Chromutogruphia 1989,27 R Kasemann and H Schmidt New J Chem 1994,18,1117 K Izumi H Tanaka M Murakami T Deguchi A Morita N Tohge and T Minami J Non-Cryst Solids 1990,121 C Sanchez B Alonso F Chapusot F Ribot and P Audebert J Sol-Gel Sci Technol 1994,2 (a) H Schmidt and B Seiferhng Mater Res Soc Symp Proc 1986 73 739 (b) H K Schmidt Muter Res Soc Symp Proc 1990,180,961 40 F Chaput D Riehl Y Levy and J P Boilot Chem Muter 1993 (a)E Toussaere J Zyss P Griesmar and C Sanchez Nun-Linear 5,589 Optics 1991 1 349 (b)C Sanchez P Griesmar E Toussaere 41 B K Coltrain,C J T Landry J M O’Reily,A M Chamberlain G Puccetti I Ledoux and J Zyss Non-Linear Optich 1992 4 G A Rakes J S S Sedita L W Kelts M R Landry and V K Long Chem Muter 1993,5,1445 J Y Sanchez A Denoyelle and C Poinsignon Polvm Adv 42 50 M E Brik J P Bayle and P Judeinstein to be published (a) P Griesmar C Sanchez G Pucetti I Ledoux and J Zyss Mu1 Eng 1991 1 205 (b) B Lebeau J Maquet C Sanchez R Hierle E Toussaere and J Zyss J Mater Chem 1994,4,1855 R H Glaser G L Wilkes and C E Bronnimann J Non-Cryst Solidr 1989 113 K J Shea D A Loy and Webster J Am Chem Soc 1992 114,6700 R J P Corriu J J E Moreau P Thepot and M Wong Chi Man Chem Muter 1992,4,1217 G M Jamison D A Loy and K J Shea Chem Muter 1993 5 D E Rodriguez A B Brennan C Betrabet B Wang and G L Wilkes Chem Mater 1992,4 J Krdmer R K Prud’homme and P Wiltzius J Colloid interface Sci 1987,118,294 F Devreux J P Boilot F Chaput and A Lecomte Phvs Rev A 1990,41,6901 P Judeinstein J Titman M Stamm and H Schmidt Chem Mater 1994,6.(a)J Cazes C R Acad Sci 1988 247 1874 (b) L W Breed R L Elliott W J Haggerty Jr and F Baiocchi J Org Chem 26 J L Speier Adv Organornet Chem 1979,17,407 D P N Satchell and R S Satchell Chem SOC Rev 1975,4,231 P Judeinstein M E Brik J P Bayle J Courtieu and J Rault Muter Res SOC Symp Proc 1994,346,537 H W Oviatt Jr K J Shea S Kalluri Y Shi W H Steier and L R Dalton Chem Muter 1995,7,493 91 99 Technol 1993,4,99 C A Vincent in Electrochemical Science and Technology of Polymers-2 ed R G Linford Elsevier Amsterdam 1990 p P Judeinstein and H Schmidt J Sol-Gel Sci Technol 1994 3 P Judeinstein P W Ohveira J P Bayle and J Courtieu J Chim Phys 1994,91,1583 Hybrid Orgunic-Inorganic Composites ed J E Mark C Y-C Lee and P A Bianconi ACS Symp Ser ,Washington DC 1995,585 Functional Monomers and Polymers ed K Takemoto Y Inaki and R M Ottenbrite Marcel Dekker New York R Yoshida K Uchida Y Kaneko K Sakai A Kikuch Y Sakurai and T Okano Nature 1995,374,240 C Guizard and P Lacan New J Chem ,1994,18,1097 D Levy J M S Pena C J Serna and J M Oton J Non-Cryst Solids 1992,147/148,646 (a) P Judeinstein J Livage A Zarudiansky and R Rose Solid Stute ionzcs 1988 28/30 1722 (b) M A Maddo and M A Aegerter J Sol-Gel Sci Technol 1994,2,667 P Audebert P Griesmar P Hapiot and C Sanchez J Muter Chem 1992,2,1293 D Vuillaume and F Rondelez La Recherche 1995,275,461 H J Watzke and C Dieschbourg Adv Colloid Interface Sci 1994,50 Cited in Chem Eng News August 1993 p M E Davis Cong-Yan Chen S L Burkett and R F Lobo Mater Res Soc Symp Proc ,1994,346,831 (a)J I Zink J S Valentine and B Dunn New J Chem 1994,18 1109 (b)D Avnir Arc Chem Res 1995,28,328 M T Reez A Zonta and J Simpelkamp Angew Chem Int Ed 57 S Dire F Babonneau J Livage and C Sanchez J Muter Chem Engl 1995,34,301 1992 2,239 58 F Babonneau Mater Res Soc Symp Proc 1994,346,949 Paper 5/03272E Received 22nd May J Muter Chem 1996 6(4) 511-525

ISSN:0959-9428    

DOI:10.1039/JM9960600511

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

~~~ ~ Synthesis of polyesters containing 9,10-diacetoxyanthracene-2,6=diylmoieties via a precursor polymer approach Ruab Uddin," Philip Hodge,"" Michael S. Chisholmb and Paul Eustaceb "Chemistry Department, University of Manchester, Oxford Road, Manchester, UK M13 9PL bICI Materials, Wilton Research Centre, PO Box 90, Middlesbrough, Cleveland, UK TS90 8JE Soluble polyesters are synthesised by polymerising a range of bis(acid ch1oride)s with the bisphenol that is formally the Diels- Alder adduct of 9,10-diacetoxy-2,6-dihydroxyanthraceneand dimethyl maleate. Heating the soluble polyesters to about 230 "C brought about retro-Diels-Alder reactions to give the insoluble target polyesters containing 9,lO-diacetoxyanthraceneresidues. There is considerable interest in polymers consisting of aro- matic units linked together directly or uiu ester, ketone, ether, thioether, sulfone, amide or imide moieties because they often form the basis of excellent high performance materials.' In many cases these polymers also display liquid crystal proper- ties.2 It can, however, be difficult to synthesise such polymers with a substantial degree of polymerisation due to their poor solubilities.This problem can sometimes be overcome by using a precursor polymer synthetic appr~ach.~ This involves syn- thesising a soluble and therefore easily characterised and processed polymer which under appropriate conditions, for example heating, undergoes a simple chemical transformation to give the target polymer. We are interested in synthesising fully-aromatic polymers containing anthraq~inone-2~6-diyl moieties 1 for several reasons.Firstly, the anthraquinone unit, though stable to high temperatures in air, has interesting chemical reactivity, for example, redox ~hemistry.~ Secondly, we have shown recently that the moiety 1 is mesogenic.' Thirdly, they can be expected 0 OCOCH-, 0 OCOCH, 1 2 to be accessible by a precursor polymer approach based on the Diels-Alder chemistry of anthracenes and thus they are potentially a type of high performance polymer that can be processed easily during synthesis. As part of a programme to investigate polymers containing moieties 1, we have synthesised a series of polyesters containing 9,lO-diacetoxyanthracene moi-eties 2.The results are reported in this paper. The moieties 2 have the potential for easy conversion into moieties 1. Several anthracene-containing polymers have been prepared before.6p12 The previous work that is most relevant to the present work is that reported by a research group at Du Pont.8 They synthesised the series of polyesters 3 via precursor polymers 4, see Scheme 1. As a consequence of the modest solubilities of the precursor polymers the molecular masses were estimated from the inherent viscosities of solutions in a 40 :60 mixture of 1,1,2,2-tetrachloroethaneand phenol. Results and Discussion The work carried out can be conveniently discussed in three parts: the synthesis of a bisphenol monomer incorporating a suitable precursor unit, polymerisations using this monomer to give precursor polyesters, and then conversion of the latter into the target polymers.Synthesis of monomer 9 and related work The initial objective was to synthesise from commercially available 2,6-dihydroxyanthraquinone(5) (anthraflavic acid) a 2,6-bisphenol monomer which was, or was formally, a Diels- Alder adduct of 9,10-diacetoxy-2,6-dihydroxyanthraceneand which would lead to precursor polymers with a significant solubility in a range of organic solvents. 2,6,9,10-Tetraacet- oxyanthracene (6) is the obvious synthetic intermediate and it was prepared in 79% yield by heating the quinone 5 with zinc dust, acetic anhydride and sodium acetate (Scheme 2). 9,lO-Diacetoxyanthracene(10) was prepared from 9,lO-anthra- quinone in a similar manner for use as a model compound.OCOCH, OCOCH3 10 OCOCH3 OCOCH3o$flF qo,cH3CH3COO CH3COO COzCH3 0 11 12 Maleic anhydride, dimethyl fumarate and methyl acrylate, being relatively rea~tive'~ and cheap, were investigated as dienophiles in Diels-Alder reactions with the above tetraace- toxyanthracene. High yields of isolated adduct were obtained only when maleic anhydride was used. This dienophile afforded adduct 7 in 79% yield. The failure of the other dienophiles to react well is consistent with the facts that maleic anhydride is the most reactive of the three dienophiles in the Diels-Alder reactions with 9,lO-dime thylant hracene,I3 and that 9,l O-diace- toxyanthracene (10) is expected to be less reactive in Diels- Alder reactions than anthracene it~e1f.l~ The diacetoxyanthra- cene (10) reacted with maleic anhydride to give Diels-Alder adduct 11.Treatment of adduct 11 with methanol containing 2% of concentrated sulfuric acid at 60 "Cfor 4 h gave what is formally the dimethyl maleate adduct 12 in 71 YOyield. The anthracene- J. Muter. Chem., 1996, 6(4), 527-532 527 where R = -(c€lz)m-(where m = 4 8 or 10) m or p phenylene Scheme 1 9 OCOCH? Zn acetic anhydnde sodium acetate * CH2COO 0 bCOCH3 5 6 maleic anhydnde in xylenei OCOCH3 OCOCH3 CH3COO q-JoCOCH3 CH3COO CH3COO\ C02CH3%H\ and isomer with H LC02H C0,CH3 and CO,H interchanged H 0 8 7 OCOCH3 9 Scheme 2 Synthesis of monomer 9 maleic anhydride adduct is reported to react similarly l5 The product was mainly half methyl ester 8 together with a minor stability of the 9-and 10-acetoxy groups in adduct 11 under amount of the required dimethyl ester 9 It IS not clear why these conditions is expected because they are esters of bridge-groups in the 2-and 6-positions should affect the course of head tertiary alcohols Adduct 7, on the other hand, did not the reactions at the anhydride group Unfortunately, attempts react as cleanly as adduct 11 with methanol and sulfuric acid to drive the reaction between adduct 7 and methanol to As expected the 9-and 10-acetoxy groups were unreactive and completion by using more vigorous conditions also produced the 2-and 6-acetoxy groups were cleanly methanolysed a complex mixture However, treatment of adduct 7 with However, the anhydride moiety reacted only partially and the methanol and sulfuric acid at 20 "Cfor 6 days cleanly gave the 528 J Muter Chern, 1996,6(4), 527-532 half ester 8 in 84% yield.The latter then reacted with ethereal fdiazomethane to give the monomer 9 in 89% yield. The reactions involved in the successful synthesis of mon- omer 9 are summarised in Scheme 2. In simple tests monomer 9 was poorly soluble in diethyl ether and chloroform but it dissolved readily in acetone, tetrahydrofuran, methanol and -R-cl"dimethyl sulfoxide. It also dissolved in an equivalent amount of 1 mol dm-3 aqueous sodium hydroxide and, after the solution had been left at 20 "C for 4h, the monomer could be recovered unchanged upon acidification.Synthesis of precursor polymers The bisphenol monomer 9 was copolymerised using two phase systems. In each case the bis-salt of the bisphenol in water was treated with a solution of the bis(acid chloride) in chloroform. Tetrabutylammonium cations served as phase transfer catalysts and the reactions were carried out for 2 h at 23°C. The precursor polymers were isolated by precipitation into meth- anol and then purified by washing and/or reprecipitation. They were characterised by elemental analysis (C and H), infrared and 'H NMR spectroscopy and GPC. The results are summar- ised in Table 1. The formulae for polymers PP1-PP9 are given in Scheme 3.For the synthesis of precursor polymers PP1 and PP2 procedure A was used. In this procedure equimolar amounts of bisphenol and bis(acid chloride) were used, the bisphenol was dissolved in aqueous sodium hydroxide and tetrabutylam- monium bromide (8 mol%) was added to provide phase trans- fer catalysis. The yields and degrees of polymerisation obtained were not very high and in an attempt to improve these results procedure B was used. In this procedure the bisphenol was neutralised using aqueous tetrabutylammonium hydroxide and no tetrabutylammonium bromide was added. The net effect is that the amount of phase transfer catalyst present was much higher than in procedure A. However, it is clear from the syntheses of precursor polymers PP3 and PP4, see Table 1, that this produced no significant improvement in the degrees of polymerisation.At this stage it was suspected that although the sample of monomer 9 appeared from 'H NMR spec-troscopy and elemental analysis to be of high purity, the purity may not in fact be very high. In procedure C, therefore, the amount of phase transfer catalyst present was kept high but the bisphenol monomer was used in a small excess (5 mol%). Using this procedure precursor polymers PP5-PP9 were pre- pared in high chemical yields and with average degrees of polymerisation in the range of from 35 to 190. All the precursor polymers obtained were soluble in chloro- form, tetrahydrofuran, N,N-dimethylformamide and dimethyl sulfoxide. Good clear films could be cast from chloroform PP1-PP9 I iheat OCOCH3 J" FP1-FP9 where PP1, FP1 R = -(CH 218-R= -+PP2, FP2 3PP3, FP3 R= PP4, FP4 R= PP5, FP5 R = -(CH2)4-PP6, FP6 PP7, FP7 PP8, FP8 PP9, FP9 Scheme 3 solutions.By differential scanning calorimetry (DSC) all the polymers were stable up to about 210"C, above which the retro-Diels-Alder reactions began to occur (see Table 2). Only precursor polymers PP1 and PP5 showed glass transition temperatures below the decomposition temperatures. The former had Tg = 121"C and the latter Tg = 179 "C. Table 1 Synthesis of precursor polyesters using monomer 9" molecular mass x polymer bis(acid chloride) procedure" yield (Yo) Mn Mw polydispersity degree of polymerisation PPl 78 18.8 41.8 2.2 59 PP2 75 4.5 11.0 2.5 15 PP3 90 5.2 13.0 2.5 17 PP4 77 3.5 6.2 1.8 12 PP5 87 12.2 23.8 2.0 35 PP6 98 43.7 82.0 1.9 122 PP7 97 20.2 52.6 2.6 52 PP8 C 99 49.7 140.0 2.8 124 PP9 ClOC mcoclC 98 72.5 174.2 1.9 190 a See Experimental section for details of method.Estimated by GPC. System calibrated using polystyrene standards. J. Mater. Chem., 1996, 6(4), 527-532 529 Table 2 Conversion of precursor polymers to final polymers and some propeties of the latter elemental analysis (%) precursor polymer final polymer TonsetloC' DSC TGA weight loss in TGA % calc YOfound A,,, of final polymerb/nm calc C found calc H found Gec/'Cc PPl FP1 214 220 23 29 337, 357, 378, 399 683 703 57 52 249 PP2 FP2 226 210 24 27 -357, 379,400 - - - - - PP3 FP3 239 229 24 26 337, 359, 379,400 684 674 35 36 - PP4 FP4 229 214 24 22 338, 359, 379, 399 684 672 35 37 - PP5 FP5 223 216 25 30 336, 357, 378, 399 661 672 46 44 249 PP6 FP6 231 210 24 27 684 673 35 36 289 PP7 FP7 247 210 21 26 380, 400 722 720 38 37 - PP8 FP8 252 231 21 25 340, 359, 379, 401 701 705 36 36 284 PP9 FP9 251 245 22 28 379, 401 711 711 36 35 27 1 TOnset=Temperatureof onset of decomposition Sample heated at 10°C min-' New absorption maxima Polymer PP9, for example, displayed A,,,/nm 342 and 356 prior to heating, due to the presence of naphthalene residues 'By DSC Conversionof precursor polymers into final polymers Heating the precursor polymers was expected to bring about retro-Diels-Alder reactions with the formation of the target polymers and the elimination of dimethyl maleate This was monitored using DSC and TGA As estimated by DSC, in the solid state the simple 9,lO-diacetoxyanthraceneadducts 11 and 12 undergo the retro-Diels-Alder reaction at 240 "C and 212 "C respectively Consistent with this it was shown by DSC that with precursor polymers PP1-PP9 the temperatures for the onset of the decompositions were in the range 214 "C to 252 "C The Du Pont researchers found that precursor polymers 4 were converted into polymers 3 at 200-300 "C The decompo- sitions of precursor polymers PP1-PP9 were also monitored by thermogravimetric analysis (TGA) As the temperatures of the samples were increased, the samples began to lose weight at temperatures in the range 210-245 "C and when this loss of weight ceased in each case the total weight loss was close to that expected for the retro-Diels-Alder reaction, see Table 2 The decompositions were also studied using UV spec-troscopy For this purpose films of the precursor polymers were cast on quartz from solutions in chloroform The films were clear and colourless After measurement of their UV spectra, the samples were heated in a vacuum oven (<1 mm of Hg) at 200 "C for 2 days The spectra were then remeasured It was found that whereas the original films showed no absorption in the 325-400nm region, after heating the films showed typical anthracene-type adsorption The Amax of the absorptions are given in Table 2 and typical spectra are shown in Fig 1 75 275 300 3SO 400 450 A /nm Fig.1 Ultraviolet spectra of precursor polyester PP5 before heating (trace 1) and after heating (trace 2) for 46 h The product is final polymer FP5 530 J Muter Chem, 1996, 6(4), 527-532 In several cases larger samples of film were prepared and the film broken up to provide samples for the measurement of infrared spectra and for elemental analyses The infrared spectra were significantly different from those of the precursor polymers, in particular the carbonyl bands due to the 9- and 10-acetoxy groups shifted from ca 1745 cm-I to ca 1780 cm-' Given the method used to prepare the samples, for example, that the films may have contained traces of dimethyl maleate, the results of the analyses (see Table 2) were reasonably close to the theoretical values Finally, it was noted that after heating to bring about the retro-Diels-Alder reactions, though the films remained clear and transparent they became pale yellow to brown in colour, suggesting some thermal decomposition Measurement of decomposition temperatures by DSC indicated, see Table 2, that decomposition generally begins at temperatures in the range 249-284°C Thus, there is a relatively narrow tempera- ture range over which the retro-Diels-Alder reactions can be effected satisfactorily Conclusions Precursor monomer 9 was synthesised from commercially available 2,6-dihydroxyanthraquinone 5 The monomer 9 was polymerised in two phase systems with a range of bis(acid ch1oride)s This gave the soluble precursor polyesters PP1-PP9, see Scheme 3 Heating the precursor polymers at ca 230 "C brought about retro-Diels-Alder reactions and the formation of the target polyesters FPl-FP9 which contain 9,10-diacetoxyanthracene moieties 2 It is of interest to note that the 9- and 10-acetoxy groups and the two methoxycar- bony1 groups in monomer 5 survive the polymerisation con- ditions Future work will attempt to use monomer 9, or close relatives, to synthesise polyethers Experimental Melting points were determined using an Electrothermal 9100 apparatus and are uncorrected Infrared spectra were recorded using a Perkin-Elmer FT-IR 1710 instrument and, except where stated otherwise, were measured as KBr discs Ultraviolet spectra were recorded using a Shimadzu UV 260 instrument 'H NMR spectra were recorded for solutions in deuteriochloroform using either a Varian Gemini 200 or a Varian Unity 500 instrument J Values are given inHz Elemental analyses were obtained from the Departmental Microanalysis Service using a Carlo Erba 1108 Elemental Analyser Gel permeation chromatography (GPC) measure- ments were carried out using 02% (w/v) solutions in tetca- hydrofuran, 4 p Styragel columns ( lo6, lo4, lo3 and 500 A), tetrahydrofuran as the eluent and a Waters 410 differential refractometer as the detector.Polystyrene standards provided the molecular weight calibration. Differential scanning calor- imetry (DSC) and thermogravimetric analysis (TGA) were carried out on samples of 5-10mg using a Seiko 220C dual purpose instrument. Sealed aluminium cells were used for DSC and open pans were used for TGA. Both were performed under an atmosphere of nitrogen with a heating rate of 10 "C min- '. Conversion of 2,6-dihydroxyanthraquinone(5) into 2,6,9,10- tetraacetoxyanthracene (6) 2,6-Dihydroxyanthraquinone ( 10.00g, 41.7 mmol), sodium acetate (8.00g, 97.7 mmol) and zinc powder (6.04 g, 92.4 mmol) were placed in a round-bottom flask. Acetic anhydride (200 ml) was added and the mixture stirred. After the exotherm subsided the mixture was vigorously stirred and heated under reflux for 5 h.As the mixture was cooled, a pale green solid precipitated. A few drops of concentrated sulfuric acid were added to destroy unchanged zinc powder. The mixture was then poured onto ice-water (1200 ml) and stirred for 2 h. The solid product was filtered off, washed with a small amount of cold ethanol and then recrystallised from acetic acid. This gave the required product 6 (10.26 g, 79% yield), mp, 281-283 "C, (lit.,I6 274 "C); vmax(Nujol rnull)/cm-l 1753; SH 2.38 (6 H; s 2-and 6-OCOCH,), 2.63 (6 H; s 9-and 10-OCOCH,), 7.30 (2 H, d, J 9.0 and 1.5, 3- and 7-H), 7.60 (2 H, d, J= 1.5, 1- and 5-H) and 7.93 (2H, d, J 9.0, 4- and 8-H) (Found: C, 64.9; H, 4.1. Calc. for C22Hl'O': C, 64.4; H, 4.1%).9,lO-Diacetoxyanthracene(10) This compound was prepared from anthraquinone using the procedure given above. 9,lO-Diacetoxyanthracene (10) was obtained in 83% yield, mp 279-280 "C (from acetic acid) (lit.,17 264-266'C); vmax/cm-' 1750; 6, 2.65 (6H, s, 9-and 10-OCOCH,), 7.55 (4H, 2-, 3-, 6- and 7-H) and 7.96 (4H, m, 1-, 4-, 5- and 8-H). DielsAlder adduct 7 from compound 6 and maleic anhydride A mixture of 2,6,9,10-tetraacetoxyanthracene (6) (1.42 g, 3.5 mmol) and maleic anhydride (0.68 g, 6.9 mmol) in p-xylene (30 ml) was heated at reflux temperature for 4 days. The mixture was cooled then the pale brown solid which formed was filtered off and dried. Recrystallisation from chloroform gave the adduct 7 (1.39 g, 79%) as white crystals, mp 234-236 "C; vmax(Nujol mull)/cm-' 1865 and 1786 (anhydride C=O) and 1762 (ester C=O); 6, 2.27 (3 H, s, 2-OCOCH3), 2.29 (3 H, s, 6-OCOCH3), 2.54 (6 H, s, 9-and 10-OCOCH,), 5.12 (2 H; s, bridge C-H), 6.95 (1 H, d, J 1.5, 1-H),6.98 (1 H; q, J 8.7 and 1.5, 3-H), 7.10 (1 H; q, J 9.2 and 2.3, 7-H), 7.20 (1 H, d, J 8.7, 4-H), 7.38 (1 H, d, J 2.3, 5-H) and 7.62 (1 H, d, J 9.2, 8-H) (Found: C, 61.0; H, 3.9.Calc. for C26H20011:C, 61.4; H, 3.9%). DielsAlder adduct 11 from 9,lO-diacetoxyanthracene10 and maleic anhydride A mixture of 9,lO-diacetoxyanthracene(10)(2.94 g, 10.0 mmol) and maleic anhydride (1.30 g, 13.3mmol) in p-xylene (25 ml) was heated at reflux temperature for 3 days. An off-white solid formed.It was collected and then recrystallised from chloro- form to give the adduct 11 (3.07 g, 83%), mp 255-257 "C, vmax/cm-1868m and 1786s (5-membered ring anhydride) and 1738s (ester carbonyl); 6, 2.58 (6 H, s, 9-and 10-OCOCH,), 5.14 (2 H, s, bridge C-H), 7.1-7.4 (6 H, m, 1--4-and 6-and 7-H) and 7.64 (2 H, m, 5-and 8-H) Found: C, 67.3; H, 4.2. Calc. for C22H1,07: C, 67.3; H, 4.1%). Reaction of adduct 11 with methanol A mixture of adduct 11 (3.00 g, 7.7 mmol) and acidic methanol (75 ml, containing 2% of concentrated sulfuric acid) was heated under reflux. Initially adduct 11 was insoluble but it slowly dissolved as it reacted. After 2 days most of the solvent was evaporated off under reduced pressure and the slurry so obtained was treated with water (50 ml).The precipitate which formed was collected, washed with copious amounts of water and dried. This gave compound 12 (2.38 g, 71%) as a white solid, mp 196-198 "C; vmax/cm-' 1755; 6, 2.45 (6 H, s, 9-and 10-OCOCH,), 3.50 (6 H, s, 2 x CO,CH,), 4.65 (2 H, s, bridge C-H), 7.20 and 7.60 (8 H, m, 8 x ArH) (Found: C, 65.5; H, 5.2. Calc. for C24H2208:C, 65.8; H, 5.0%). Reaction of adduct 7 with methanol (a)Adduct 7 (2.00 g, 3.9 mmol) was treated with acidic meth- anol (35 ml, containing 2% of concentrated sulfuric acid) at reflux temperature for 24h. Most of the solvent was then evaporated off under reduced pressure, a mixture of water and methanol (1 :1, 30 ml) was added, and the pH was adjusted to 7 using dilute aqueous sodium hydroxide.The product was then extracted with ethyl acetate (30 ml x 3). The combined extracts were dried (magnesium sulfate) and evaporated to dryness (0.43 g, ca. 23%). Analysis by 'H NMR spectroscopy in comparison with the spectrum (see below) of an authentic sample of monomer 9 indicated that whilst the product was mainly monomer 9 it contained substantial impurities. Presumably the main product was half acid 8 and this formed the sodium salt of the acid at the time the pH was adjusted. (b) Adduct 7 (8.00 g, 15.7mmol) was treated with acidic methanol (60 ml, containing 1% of concentrated sulfuric acid) at 20°C for 6 days. A clear solution eventually formed. Most of the solvent was evaporated off under reduced pressure and the residue was added to ice-cold water (100 ml).A precipitate formed which was collected, washed with water and dried. This gave half acid 8 (6.03 g, 84%) which decomposed without melting at ca. 190 "C; v,,,(evaporated film)/cm-' 3402s, br (carboxylic acid 0-H stretch) and 1745s, br (C=O stretch of 3 ester groups and 1 carboxylic acid group); 8, 2.30 (6 H, s, 9-and 10-OCOCH,), 3.45 (3 H, s, C02CH3), 4.45 (2 H, s, 2 x bridgehead C-H), 6.50-7.25 (6 H, m, 6 x Ar-H) Found: C, 60.1; H, 5.0. Calc. for C23H22010: C, 60.3; H, 4.8%). Methylation of compound 8 using diazomethane A solution of compound 8 (2.00 g, 4.4 mmol) in tetrahydro- furan (30 ml) was treated with ethereal diazomethane (pre- pared'' from N-methyl-N-nitrosotoluene-p-sulfonamide)until the yellow colouration persisted. The excess of diazomethane was then destroyed by the addition of a few drops of acetic acid.Most of the solvent was removed under reduced pressure and the residue added to diethyl ether. The precipitate was collected and recrystallised from a mixture of tetrahydrofuran and hexane. This gave monomer 9 (1.83g, 890/), which decom- poses without melting at ca. 220"C, vmaX/cm-' 3401 m, br (OH)and 1746s,br (OCOCH, and C02CH3 C=O); 6,(C2H6]-DMSO) 2.35 (6 H, s, 9-and 10-OCOCH,), 3.38 (6 H, s, 2 xC02CH,), 4.40 (2 H, s, bridgehead C-H) and 6.5-7.3 (6 H, m, ArH) (Found: C, 61.5; H, 5.0. Calc. for C2,H2,010: C, 61.3; H, 4.7%). Polymerisations The following procedures are typical. The results of all the polymerisations are summarised in Table 1.Procedure A: synthesis of polymer PP1. Monomer 9 (1.043 g, 2.22 mmol) was dissolved in a vigorously stirred solution of aqueous sodium hydroxide (0.178 g, 4.45 mmol of sodium hydroxide in 20 ml of water) and tetrabutylammonium bromide J. Muter. Chem., 1996, 6(4), 527-532 531 (56 mg, 8 mmol) was added When the mixture was homo- geneous a solution of sebacoyl chloride (0 531 g, freshly dis- tilled) in chloroform (15 ml) was added rapidly and the mixture was stirred vigorously for 2 h at 20°C Stirring was then stopped and the organic layer added to acidic methanol (600 ml of methanol containing a few drops of concentrated hydrochloric acid) This precipitated the polymer It was collected and washed successively with copious amounts of water then a small amount of methanol and then dried to give the product PP1 (1 25 g, 78%), v,,,(evaporated film from chloroform)/cm-' 1745 (ester groups), 6, 140 (8 H, br s, central 4 methylenes of aliphatic chain), 170 (4 H, br m, two methylenes of aliphatic chain), 240 (6 H, s, 9-and 10-OCOCH3), 2 50 (4 H, br m, 2 x -CH2CO-), 4 50 (2 H, s, 2 x bridge C-H), 7 0-9 0 (6 H, m, ArH) (Found C, 63 5, H, 5 9 Calc for (C&t3@1()),, C, 64 2, H, 5 7%) Procedure B synthesis of polymer PP3.Monomer 9 (2 303 g, 4 9 mmol) was neutralised with aqueous tetrabutylammonium hydroxide (6 300 g of a 40% solution, 9 7 mmol) Water (15 ml) was added and the mixture was stirred vigorously until the mixture was homogeneous A solution of isophthaloyl dichlor- ide (0986 g, 49mmol) in chloroform (20ml) was added quickly The mixture was stirred vigorously for 48 h at 20°C under a nitrogen atmosphere The product was isolated using the procedure outlined above to give polymer PP3 (261g, 90"/0), v,,,(evaporated film from chloroform)/cm-' 1745, 6, 2 45 (6 H, s, 9-and 10-OCOCH,), 3 50 (6 H, s, 2 x C02CH,), 4 75 (2 H, s, bridge C-H) and 7 00-9 00 (10 H, m, 10 x ArH) (Found C, 63 0, H, 4 1% Calc for (C32H24012)n C, 64 0, H, 40%) Procedure C: synthesis of polymer PP7.Monomer 9 (2 923 g, 6 20 mmol, assuming 95% pure 5 91 mmol), sodium hydroxide (0 390 g, 9 75 mmol) and aqueous tetrabutylammonium hydroxide (563 mg, 2 23 mmol in 60 ml of water) were stirred together for 5 min 4,4'-Biphenyldicarbonyl dichloride (1 654 g, 5 9 mmol) in chloroform (60 ml) was added rapidly and the two-phase system was vigorously stirred at 20 "C for 24 h The product was isolated using the procedure outlined above to give polymer PP7 (3 92 g, 97%), v,,,(film formed by evapor- ation of a chloroform solution)/cm-' 1757 and 1740, dH 245 (6 H, s, 9- and 10-OCOCH,), 3 50 (6 H, s, 2 x C02CH,), 4 75 (2 H, s, 2 x bridge C-H), 7 0-7 7 (6 H, m, aromatic H of adduct), 7 80 (4 H, d, 4 x biphenyl ArH 'inner') and 8 30 (4 H, d, ArH next to biphenyl C=O (Found C, 66 5, H, 4 3 Calc for (C38H28012)n C, 67 4, H, 4 1%) Conversion of precursor polymers into final polymers The conversions of the precursor polymers into the final polymers were monitored by DSC and by TGA using ca 5 mg samples The results are summarised in Table 2 To monitor the conversions by UV spectroscopy, films of the precursor polymers ca 1 mm thick were cast from solutions in chloroform onto quartz microscope slides UV spectra were measured, then the films were heated in a vacuum oven (< 1 mm Hg) at 200 "C for 2 days UV spectra were again measured In most cases thicker films, ca 2 mm thick, of the precursor polymer were cast in Petri dishes from chloroform solutions and heated in a vacuum oven as before The films of the final polymers were broken up and the pieces used to measure FT- IR spectra, Get, and for elemental analyses The results from the latter two measurements are summarised in Table 2 We thank the SERC (now EPSRC) and ICI (Wilton) for a CASE Students hip References 1 Comprehensive Polymer Science, ed G Allen and J C Bevington, Pergamon, Oxford, 1989, vol 7, pp 473-592 2 M G Dobb and J E McIntyre, Adv Polym Sci , 1984,60/61,61 3 Important recent examples are discussed in the following refer- ences R A Dine-Hart and W W Wright, J Appl Polym Scz, 1967, 11, 609, V Chaturvedi, S Tanaka and K Kaeriyama, Macromolecules, 1993, 26, 2607, D R Gagnon, J D Capistran, F E Karasz, R W Lenz and S Antoun, Polymer, 1987,28,567 4 See, for example, T Yamamoto and H Etori, Macromolecules, 1995,28,3371 5 H C Coles, E Corsellrs, P Hodge and J -H Liu, manuscript in preparation 6 G Montaudo, P Finnochicero and J Caccamese, J Polym Sci Part A, 1971,9,3627 7 A H Frazer, B C Anderson, L C Garver and T Fukunaga, J Polym Sci Polym Chem Ed, 1985,23,2779 8 A H Frazer, B C Anderson and T Fukunaga, J Polym Scr Polym Chem Ed, 1985,23,2791 9 K Al-Jumah and J E Fernandez, Macromolecules, 1987,20, 1181 10 D Blenden and K Mullen, Chem Ber , 1988,121,1187 11 M W Pelter and J K Stille, Macromolecules, 1990, 23,2418 12 K R Gorda, R Varadaraj, D G Peiffer and C Brons, Polymer, 1992,33,1796 13 J Sauer, H Wiest and A Mielert, Chem Ber , 1964,97,3183 14 A Mielert, C Baig, J Sauer, J Martelli and R Sustmann, Liebigs Ann Chem , 1980,954 15 W E Bachmann and L B Scott, J Chem Soc, 1948,70,1458 16 0 Lieberman, Chem Ber ,1888,21,1172 17 H Cho and R G Harvey, J Chem SOC Perkzn Trans 1,1976,836 18 Vogel s Textbook of Practical Organic Chemistry, ed B S Furniss, A J Hannaford, V Rogers, P W G Smith and A R Tatchell, Longman Scientific and Technical, Harlow, England, 4th edn , 1978, p 291 (method 2) Paper 5/06304C, Received 25th September, 1995 532 J Muter Chem, 1996, 6(4), 527-532

ISSN:0959-9428    

DOI:10.1039/JM9960600527

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

_____~~~~~~~ Paramagnetic liquid-crystal side-chain polyacrylates containing Schiff base copper(11) complexes Eduardo Campillos, Mercedes Marcos,* JosC Luis Serrano, Pablo J. Alonso and Jesus I. Martinez Instituto de Ciencia de Materiales de Aragh, Facultad de Ciencias, Universidad de Zaragoza-CSIC, 50009-Zaragoza, Spain Polymers containing Schiff base copper complexes were synthesized from thermotropic liquid-crystalline polyacrylates containing a mesogenic bidentate Schiff base as the side chain. The introduction of the copper atoms (5-65 mol%), gave rise to cross-linked polymeric chains, and the copper content of the polymers was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The liquid-crystal properties were examined by differential scanning calorimetry (DSC), polarizing microscopy and electron paramagnetic resonance (EPR) spectroscopy.The mesophases of the original polyacrylate are enantiotropic smectic A and smectic C, whereas polymers containing the bis( Schiff base)copper(n) complex in different proportions exhibit an enantiotropic smectic C mesophase. The EPR measurements of this type of copper-coordinated polymer at different temperatures indicate a restricted motion of the copper complex around the long molecular axis and provided information on the local order of the molecules in the liquid-crystal phase. Since the original works of Ringsdorf, Finkelmann and co- workers'.' the development of mesomorphic side-chain poly- mers has been considerable.The incorporation of metal ions into polymeric chains to obtain metal-containing mesogenic polymers gives rise to possible attractive applications, in addition to their academic intere~t.~ Indeed, the rich variety of geometries found in metal complexes opens up new possibilities for the structural design of liquid-crystalline polymers. Metal atoms may also introduce unusual physical properties, which can be combined with the processing of polymers. We are particularly interested in the incorporation of para- magnetic moieties into liquid-crystalline polymers because the presence of paramagnetic atoms distributed along polymeric chains can yield extremely valuable information on the macro- molecular orientation. Recently we have made a series of hydroxy-functionalized liquid-crystal polya~omethines~~~ and studied the observed modifications in both the structure and the mesogenic properties caused by the introduction of para- magnetic centres into the polyazomethines.Continuing this line of work, in this paper we present a study on the introduction of copper(11) centres in a polyacrylate containing an ortho-hydroxy Schiff base (P) and their effect on the mesogenic properties of these materials. In addition, we report an EPR study of these compounds. The amount of copper is theoretically increased between 5 and 65 mol%. The polymers containing copper are denoted by CuPn, where n represents the metal content in the metal-chelated Schiff base units. Schiff base copper(I1) complexes are well known as stable, low molecular mass liquid crystals having a wide mesogenic range.The same type of polymer has been synthe- sized by Galyametdinov et aL6 but the mesomorphic property was not reported. To our knowledge only thermotropic liquid- crystal pol y (acrylate ester) s with bis( P-diketonato)copper (II)~,~ side chains (similar to the polymers described here) are known to date. Experimental Characterization Microanalysis was performed with a Perkin-Elmer 240B micro- analyser. The copper content was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES) using a Perkin-Elmer P-40 spectrometer. The average molecu- lar mass of the polymer was determined by gel-permeation chromatography (GPC) in tetrahydrofuran (THF) using two columns in series, Progel-TSV G3.000 Fnd G2509 HXL from Teknokoma and Ultrastyragel (lo4 A and 500 A) from Millipore, and calibrated with polystyrene standards.IR spec- tra were recorded with a Perkin-Elmer 1600 (series FTIR) spectrometer over a 400-4000 cm-' spectral range. 'H and I3C NMR spectra were recorded on a Varian Unity-300 spectrometer operating at 300 MHz using CDCI, as solvent. Transition temperatures were determined by differential scanning calorimetry (DSC) using a Perkin-Elmer DSC-7 with heating/cooling rates of 10 "C min-', under a nitrogen atmos- phere. The temperatures were read as the maximum of the endothermic peaks. The apparatus was calibrated with indium (156.6"C, 28.45 J g-I) and tin (233.1 "C, 60.5 J g-I). The textures of the mesophases were studied with either a Nikon or an Olympus BH-2 polarizing microscope, equipped with a Mettler FP82 hot-stage and a FP80 control unit or a Linkam THMS600 hot-stage with a TMS91 central processor and a CS196 cooling system.The samples were investigated using cross-polarizers at room temperature and at elevated tempera- tures with a magnification of 275 x. Powder X-ray diffraction (XRD) patterns were obtained with a Guiaier diffractometer (Huber 644) using a Cu-Ka, (A= 1.5405 A) beam from a germanium monochromator. The samples were held in rotating Lindemann glass capillaries (d= 0.5 mm) and heated with a variable temperature attachment. The diffraction patterns were registered by a scintillation counter. X-Band EPR measurements were recorded with an ESP380E Bruker spectrometer working in continuous mode.An ER 41 11VT variable temperature accessory from Bruker was used for measurements above room temperature (RT). Powder samples were put into quartz tubes (707-SQ from Wilmad) and the temperature was monitored using a copper-constantan thermocouple attached to the tube. The error in the tempera- ture was estimated to be lower than 0.5"C and the stability was better than 0.1 "C. Synthesis The synthesis of the liquid-crystalline polyacrylate was carried out following methods described in the literat~re.~ The general reaction pathway to the target polyacrylate (P)and the poly- acrylate-containing copper complexes (CUP) is shown in Scheme 1.J. Mater. Chem., 1996, 6(4),533-538 533 4-( 10-Acryloyloxydecy1oxy)salzcylaldehyde 3 A mixture of 2 HO &0 Br(CH2) $3 -Br("&l,oo~( HMPA C (40 mmol), sodium acrylate (80 mmol) and hexamethylphos- H KHCOJaacetme H C+CHCOONa' 1 2 I o=c CuPn Scheme 1 Materials. All the solvents used were reagent grade obtained from Scharlau and were purified using standard literature procedures prior to use Chemicals and reagents were obtained from Aldrich Chemical Co and Fluka When required, reagents were purified by either recrystallization or distillation prior to use Monomer synthesis. 4-(10-Bromodecy1oxy)salicylaldehyde 2 This was prepared following a literature method" by the reaction of 2,4-dihydroxybenzaldehyde 1 (90 mmol) with 1,lO- dibromodecane (85 mmol) in acetone (100 ml), using potass- ium bicarbonate (KHCO,, 85 mmol) as a base to avoid the alkylation of the OH group in position 2 of the benzene ring Yield 50%, mp 47 "C, 'H NMR 6 11 45 (s, 1 H, OH), 9 67 (s, 1 H, CHO), 7 39 (d, 1 H, J=8 7 Hz, salicylidene), 6 49 (dd, 1 H, J=8 7, 2 3 Hz, salicylidene), 6 38 (d, 1 H, J=2 3 Hz, salicylidene), 3 97 (t, 2 H, J=6 5 Hz, CH,O), 3 38 (t, 2 H, J= 6 7 Hz, CH,Br), 1 9-1 2 (m, 16 H, CH, groups), I3C NMR 6 19423 (1 C, CHO), 16639, 16447, 135 15, 11496, 108 70, 10101 (6 arom C), 68 51 (1 C, CH,), 33 96 (1 C, CH,Br), 32 74, 29 32, 29 24, 29 18, 28 84, 28 65, 28 08, 25 83 (8 C, CH, v/cm-' 1670 (CHO) yellow to brown depending on the amount of copper coordi- groups), IR (NuJo~) phoramide (HMPA, 75 ml) was stirred at 60 "C for 15 h The reaction mixture was cooled to room temperature and poured into water Compound 3 precipitated and was purified by column chromatography using CH,C1, as an eluent Yield 70%, mp 53 "C, 'H NMR 6 11 46 (s, 1 H, OH), 9 68 (s, 1 H, CHO), 7 39 (d, 1 H, J =8 7 Hz, salicylidene), 6 50 (dd, 1 H, J = 8 6, 2 2 Hz, salicylidene), 6 39 (d, 1 H, J =2 2 Hz, salicylidene), 638 (dd, 1 H, J=173, 16Hz, alkene), 6 10 (dd, 1 H, J=173, 10 3 Hz, alkene), 5 79 (dd, 1 H, J= 104, 1 6 Hz, alkene), 4 13 (t, 2 H, J=6 7 Hz, CH20CO), 3 98 (t, 2 H, J =6 5 Hz, CH,O), 1 8-1 2(m, 16 H, CH2 groups), I3C NMR 6 194 24 (1 C, CHO), 166 27 (1 C, COO), 16640, 16448, 135 15, 114 96, 108 71, 10100 (6 arom C), 130 38 (1 C, alkene), 128 60 (1 C, alkene), 68 51 (1 C, CH,O), 64 61 (CH,OCO), 29 34,29 20,29 14,28 85, 28 54,25 88,25 84,25 83 (8 C, CH, groups), IR (NuJo~)vlcm-' 1712 (OCO), 1627 (HCO), 1635 (C=C) N-4'-Pentyloxyphenyl-4-(n-acryloyloxydecyloxy)salicylaldi-mine 4 This was synthesized using a well known method'' by mixing an ethanolic solution of 3 (28 mmol) with 4-pentyloxy- aniline (28 mmol) and 2 drops of acetic acid as a catalyst The product was purified by recrystallization from absolute ethanol Yield 75%, transition temperatures/"C K 64 5 SA 83 8 N 89 1 I, 'H NMR 6 1392 (s, 1 H, OH), 848 (s, 1 H, CH=N), 7 21 (d, 1 H, J=8 8 Hz, benzyl), 7 20 (d, 2 H, J=8 9 Hz, N-aryl), 6 90 (d, 2 H, J=8 8 Hz, N-aryl), 6 46 (d, 1 H, J= 14 Hz, benzyl), 6 44 (dd, 1 H, J=8 8, 14 Hz, benzyl), 6 38 (dd, 1 H, J= 17 3, 1 6 Hz), 6 10 (dd, 1 H, J= 17 3, 10 3 Hz, alkene), 5 79 (dd, 1 H, J=lO3, 16 Hz, alkene), 4 13 (t, 2 H, J=67 Hz, COOCH,), 3 97 (t, 2 H, J= 6 5 Hz, CH20), 3 95 (t, 2 H, J= 6 6 Hz, OCH,), 1 8-1 3 (m, 22 H, CH, groups), 0 86 (t, 3 H, CH3) Preparation of the homopolymer P.Polyacrylate (P) was prepared by frec-radical polymerization in solution with 2,2'- azobisisobutyronitrile (AIBN) as initiator The monomer (6 mmol) was dissolved in toluene (15 ml) and polymerized under nitrogen for 24 h at 70 "C with AIBN (0 5 mol%) The reaction mixture was introduced into a Schlenk tube and thoroughly degassed by the conventional freeze-thaw tech- nique The polymer was precipitated into an excess of cold methanol and purified by dissolution in chloroform and pre- cipitation from cold methanol three times (yield 75%) The characterization data, IR, yield, microanalysis, molecular mass (determined by GPC) and polydispersity ratio (M,/M,) are gathered in Table 1 The optical and thermal data are collected in Table 2 Incorporation of transition-metal ion into polymer P.Preparation of CUP Polymer P (500mg) was dissolved in a mixture of chloroform-ethanol (11, 30 ml), Cu(OAc), *H,O was added (in amounts varying between 5 and 65 mol%) in ethanol (5 ml) and the mixture stirred under reflux for 1 h After adding ethanol, a precipitate (CUP, changes from dark Table 1 Microanalytical data, content of metal-chelated Schlff units, yields, molecular mass, polydispersity ratio (M,/M,) and IR data for the polymers compound C(%) H(%) N(%) ~~~ ~ P CUP5 CUP10 Cup15 73 2(73 1) 731(727) 726(727) 72 6(72 3) 8 4(8 5) 85(85) 84(84) 8 3(8 4) 2 6(2 7) 26(27) 27(27) 2 7(2 7) Cup20 72 5(72 3) 8 3(8 4) 2 7(2 7) Cup65 71 4(712) 8 2(8 2) 2 6(2 7) Cu added (mol%) -5 10 15 20 65 IR data/cm ' Cu found (mol%) yield(%) M, M,/M, v(C00) v(C=N) -3 57 7 53 10 58 75 95 95 95 25000 199 1728 1725 1725 1724 1620 1619 1620 1620 15 51 95 1724 1618 35 60 95 1724 1614 534 J Mater Chem, 1996, 6(4), 533-538 Table 2 Optical" data and transition temperaturesb ("C) for the heating process determined by polarizing microscopy and DSC measurements P g 52 M 72 S, 91' SA 159 I CUP5 g 49 M 80 S, 174 I CUP10 g 49 M 78 S, 174 I CUP20 g 49 M 80 S, 183 I Cup65 g 52 M 80 S, 202 I a g =glassy, M =ordered smectic phase not identified, S, =smectic A phase, S, =smectic C phase, I =isotropic liquid.Temperature data taken at the maximum of the peak. 'Data from optical microscopy. nated) was collected and washed with methanol. The charac- terization data, IR, yield, microanalysis and content of metal- chelated Schiff base units are gathered in Table 1. Optical and thermal data are collected in Table 2. Results and Discussion Synthesis and characterization of the polymers The synthesis of the polyacrylate P from monomer 4 was carried out by free-radical polymerization in solution with AIBN as initiator and toluene as solvent at 70°C (Scheme 1). The polymerization conditions were chosen after studying the effect of changing the initiator amount (0.5, 1, 2 mol%), solvent (toluene, THF) and reaction temperature (60 or 70 "C).The results of the effectivity of the polymerization with respect to the molecular masses obtained are shown in Table 3. From these experiments it was observed that higher molecu- lar masses (a molecular mass of 25.000~ was obtained by GPC) were found for polymerization in toluene with 1 mol% initiator concentration, working at 70 "C. This result is in accordance to that described in the literat~re.~ The synthesis of the metal-chelated polymers (CuPn) was carried out by adding several mole ratios of the metal salt [Cu(OAc), H,0] to a solution of the Schiff base polymer in a mixture of chloroform-ethanol (1:l) heated to reflux temperature. All the polymers synthesized were solids at room tempera- ture.The polyacrylate P (without copper) and the monomer Schiff base were yellow. The copper-chelated polymers CUP show colours ranging from dark yellow to dark brown, depending on the amount of copper coordinated to the polymer. The solubility of these polymers depends on the concen- tration of the copper in the structure. The pristine polyacrylate P is highly soluble in chlorinated solvents and in toluene. This solubility decreases markedly as the copper content increases. Thus, the polyacrylate with 36 mol% copper (CuP65) is totally insoluble in common organic solvents.This behaviour is due to the cross-linking of the polymer which increases as the amount of coordinated copper is increased. This cross-linking prevents the penetration of the solvent molecules into the network and as a result the solubility of the polymer diminishes. Mesogenic and thermal properties The optical and thermal data of the monomer and the polymers are gathered in Table 2. The mesophases were characterized Table 3 Polymerization conditions AIBN (mol%) solvent T/"C Mw 1 THF 70 1200 0.5 THF 70 1300 1 THF 60 900 0.5 toluene 70 24000 2 toluene 70 22000 1 toluene 70 25000 1 toluene 60 24000 by optical micros~opyl~,'~ and confirmed, in some cases, by XRD studies.Transition temperatures were determined by DSC and the data were taken during the heating process. N-4-pentyloxyphenyl-4-(n-acryloyloxydecyloxy)salicylaldi-mine 4. This compound exhibited nematic (N) and smectic A (S,) mesophases. The SA mesophase showed the typical tex- tures and features, i.e. it was fanshaped and became homeo- tropic when subjected to mechanical stress. The N phase showed a homeotropic texture over its entire temperature range, and upon heating the sample some nematic droplets with extinction crosses were observed in the transition to the isotropic liquid (I). The two homeotropic textures belonging to the SA and N phases are easily distinguishable because the nematic phase flashes when it is subjected to mechanical stress.Polyacrylates. All the polymers, P and CUP showed meso- genic behaviour. S, and Sc mesophases were exhibited by the pristine polymer, whereas copper-containing polymers only showed the Sc mesophase. The Sc mesophase exhibited a broken focal-conic texture which became pseudohomeotropic when subjected to mechanical stress. The SAmesophase showed a fan-shaped texture which was transformed to oily streaks and homeotropic textures by mechanical stress. Fig. 1 shows some micrographs of different textures exhibited by polyacryl- ate P taken at different temperatures. The metal-chelated Schiff base polymers form viscous liquid- crystal phases. The viscosity of the mesophase rises with an increase in the metal content of the polymer, and this indicates an increase in cross-link density.The texture of the liquid- Fig. 1 Micrograph of (a)the fan-shaped texture (at 144 "C) and (b)the oily streak texture (at 121 "C) of the S, mesophase polyacrylate, P (crossed polarizers; 275 x) J. Muter. Chem., 1996, 6(4), 533-538 535 crystal phase was identified by polarizing microscopy It was assigned as an S, phase on the basis of its sanded texture (Fig 2) The XRD pattern of this phase (Fig 3) showed one sharp peak at small angles, the spacing of which was calculated as 39 A, and a broad reflection at wide angles which corre- sponds to melting of the alkyl chains Hence, it could be concluded from the texture and the XRD pattern that this liquid-crystalline phFse was identified as an S, phase having a layer spacing of 39 A DSC results (see Table 2) indicate that the polymers exhibit a glass transition temperature (T,)at 52 "C for the polyacrylate P and around 48°C for CuPn materials A decrease in the glass transition temperature of the copper-containing polymers with respect to the pristine polymer is observed, whereas no evaluable differences were detected for the different contents of metal-chelated Schiff base units However, the clearing temperatures increase as the copper content increases and gives rise to wider mesophase ranges This mesogenic behaviour indicates that the introduction of copper atoms into the pristine polymers gives rise to significant cross-linking owing to coordi- nation of the different polymeric chains This cross-linking leads to a reduction in the mobility of the mesogenic units with a concurrent increase in the viscosity, as reported pre- viously, and also to an increase in the &-I transition tempera- ture Fig 4 shows a DSC thermogram corresponding to the CUPS polymer EPR Measurements The EPR spectra measured at RT of randomly oriented CuPn samples are given in Fig 5 For the lowest copper concen-Fig.2 Micrograph of the Sc phase at 168°C of the polyacrylate, CUP10 (crossed polarizers, 275 x) 2Ndegrees Fig.3 XRD pattern of polymer P The sample was obtained from solution without quenching or annealing oi1 00-1---r-I--7 _1 00 500 1000 1500 ' TPC Fig. 4 DSC thermogram corresponding to the CUPS polyacrylate (scan rate 10°C min ') n 65 20 15 10 5 I I I I I 0 26 030 0 34 0 8 magnetic fieldR Fig.5 EPR spectra, measured at RT, of several CuPn samples with different Cu contents, n trations (n<20%) all the traces basically coincide and the only difference between them is the broadening of the lines which increases with the metal content All of these spectra consist of three clearly resolved parallel features together with a perpendicular one at higher field (ca 340 mT) Such EPR spectra are typical of isolated Cu2+ entities having a local symmetry close to axial l4 The three parallel signals at low fields form a part of four parallel signals centred at ca 312 mT These four lines are due to the hyperfine (HF) interaction of the unpaired electron with the copper nucleus (copper has two natural abundance isotopes with I= 3/2 63Cu, 69 2% and 65Cu, 308%, having very close nuclear g-factors, so the HF interactions of both are practically indistinguishable) The following standard spin-Hamiltonian is used to describe these EPR spectra x=pB {g,(S,BxfS,B,)+gl(S,B,} +Al(Sxlx+ SyIy)+A lSzlz (1) with S =1/2 and I =3/2, only the Zeeman and HF contributions characterised by the principal values of the g-tensor (gll and 8,) and of the HF tensor (All and A,) are included pB represents the Bohr magnetron A fitting of the calculated spectrum using eqn (1) to the experimental one yields values for the spin-Hamiltonian parameters of gll=2 24 f0 01, g, = 2 04 f0 01, All=553 f10 MHz, and Al <60 MHz, which agree well with those found for Cu2+ in similar compounds and correspond to the situation in which the unpaired electron is in a Ix2-y2) orbital in which the charge points towards the four ligands in the plane l4 l6 536 J Muter Chem, 1996, 6(4), 533-538 For greater copper concentrations (n >20%) the EPR spec- trum suffers modifications.The parallel signal disappears and the perpendicular one moves towards low field in such a way that only a broad line with no resolved structure is observed in the central part of the spectrum. This type of signal has been observed in some copper compounds and it is due to Cu2 ions interacting through magnetic exchange.This inter- + action induces a collapse of the HF splitting and, if the molecular axes of the individual molecules do not maintain a parallel arrangement, an averaging of the g-factors takes The evolution of the EPR spectra has been measured as a function of temperature, between RT and 250 “C.This tempera- ture range covers the crystalline, smectic and isotropic phases. In the case of highest concentration samples we only observed an enhancement of the averaging effect. More interesting behaviour is observed in the thermal evolution of the low concentration samples, In Fig. 6 we show the CUPS EPR spectrum measured at different temperatures. Besides a broad- ening of the lines as the temperature increases, a decrease in the apparent parallel HF splitting together with a shift of the whole parallel signal towards higher field is observed.In Fig. 7(a)we show the thermal evolution of the effective parallel HF coupling constant, A,,’( T), obtained from the analysis of the EPR spectra. The evolution of the effective parallel g-factor, g,,’(T), is given in Fig. 7(b).In both cases a monotonous decrease is observed. The thermal evolution of the spectrum is an indication that a dynamic process which is thermally activated, has some 0.29 0.33 0.37 magnetic field/T Fig. 6 Thermal evolution of the EPR spectrum of a CuPS sample I a a a 420 a t-K I s I(./ influence on the copper units. A sketch of a copper paramag- netic unit linking two polymeric chains is given in Fig.8, where the molecular axes are also indicated. Since our spectra can be understood as being due to an axial Cu2+ entity the molecular axes will be taken also as the magnetic ones, the x-axis being the parallel axis for the spin-Hamiltonian tensors. It is worth noting that, owing to the cross-linking structure, the motional behaviour of our copper complexes is very different from that of classical paramagnetic probes in liquid crystals used to study order by EPR.19-23 In these works, samples become oriented by the measuring magnetic field and reorientation of the long (2) axis causes modifications on the EPR spectra. In this way, information on the order of the director can be obtained. In our case, reorientations of the z-axis are strongly hindered and slowed because of the complex bonding to two different polymer chains.Thus this axis will not affect the EPR spectrum. On the other hand, the side units of the polymer contain -0-(CH,),, -0-groups which allow almost free rotation of such a lateral unit. So it is reasonable to assume that the copper paramagnetic entity can rotate around its z-axis (see Fig. 8). The bonding to the two main polymeric chains as well as to the units packing in the mesophase introduces a restoring force and we can describe this motion as a torsional (reorien- tational) one. This mode can be detected by EPR spectroscopy since the sample is not oriented by the measuring magnetic field. Thus, we find that a reorientation mode is responsible for the thermal evolution of the spectrum. We can analyse our results in the same way as those of spin probes in liquid crystals previously reported,”-23 bearing in mind that the motion in our case is distinct and therefore the experiments give different information. The EPR spectra of copper entities can be described by the following spin-Hamiltonian: where S= 1/2 and I=3/2.The effective parameters g,’ and A,‘ are given as a function of the corresponding static case Ceqn. (1)1by: where # is the torsion angle in the x-y plane and ( ) means the averaging torsional motion. In such a situation we define a variation parameter for the a a a a a 0 I s l I J. Muter. Chem., 1996, 6(4), 533-538 537 50 I Fig.8 Sketch of the copper paramagnetic unit linking two polymeric chains The axes chosen in the text are also given EPR spectrum (3) SEPRcan be derived from the EPR data (see Fig 7) In particular from the parallel parameters it follows or (4) In our case, SEPRtakes values close to unity at RT and monotonously decreases as the temperature increases It is worth noting that no modification of this tendency is found for the K-Sc or Sc-I phase transitions On the other hand, the values for SEPRare noticeably higher than 0 5 (the value predicted for free rotation around the z-axis) in agreement with our assumption of restricted motion for the copper paramagnetic entities as a consequence of the restoring poten- tial Although the actual form of such a potential well is not known, a very simple model (see Fig 9) in which the highest probability for the orientation of the molecules is found into the potential well can be used to estimate its width If we take this probability equal to unity we obtain the estimated#,,, the copper complex is in a narrow well which expands (because amplitudes given in Fig 10 Within this model OK S1 I 0 1 I I I 0 50 100 150 200 250 TIT Fig.10 Estimation of the amplitude for the torsion of the copper paramagnetic unit as a function of temperature (see text) the smectic A arrangement was disrupted in the copper- containing polymers owing to the statistical incorporation of the copper(I1) ions, and the metal-chelated polymers (CuPn) exhibited smectic C phases only EPR spectroscopy provided information on some dynamic aspects of the behaviour of the copper chelates in our liquid-crystal side-chain polymer and indicated a restricted motion of the copper complex around the long molecular axis The authors would like to sincerely thank Dr Joaquin Barbera for his X-ray diffraction work This work has been sponsored by the CICYT (Spain) under contract MAT93-0104 and the DGICYT (Spain) under project PB92-0040 References 1 H Finkelmann, H Ringsdorf and J R WendoriT, Makromol Chem, 1978,179,273 2 H Finkelmann and G Rejage, Makromol Chem Rapid Commun, 1980,1,31 3 L On01 and J L Serrano, Adu Muter, 1995,76,348 4 P J Alonso,J I Martmez, L 01-101,M Piiiol and J L Serrano,Adu Muter, 1994,6,663 5 L Onol, P J Alonso, J I Martinez, M Pliiol and J L Serrano, Macromolecules,1994,27, 1869 6 W Haase, K Gnesar, E A Soto Bustamante and Y G Galyametdinov,Polym Muter Sci Eng ,1994,71,795 7 K Hanabusa, T Suzuh, T Koyama, H Shrai and A Kurose, Polym J, 1990,22,183 the temperature rises We should point out that this estimation of thermal expansion and thermally induced disorder) when 8 K Hanabusa, T Suzuki,T Koyama and H Shira, Makromol Chem , 1992,193,2149 has been carried out for the interchain x-axis in a static situation Conclusions Cross-linked polymers can be produced by the coordination of copper (11) ions by salicylaldimine polyacrylate Whereas the polyacrylate exhibited smectic C and smectic A mesophases, ENERGY POTENTIAL -~~~~~ 3x/2 0 xi2 x Q/radians Fig.9 Illustration of a potential for the copper entity motion The shaded regon corresponds to the highest probability for the orientation given by 4 (see text) 538 J Muter Chem, 1996,6(4), 533-538 9 M Portugall, H Rtngsdorf and R Zentel, Makromol Chem, 1982, 183,2311 10 M Artigas, M Marcos, E Melendez and J L Serrano, Mol Cryst Liq Cryst, 1985,130,337 11 P Keller and L Liebert, Solid State Phys Suppl, 1978,14, 19 12 D Demus and L Rtchter, Textures of Liqud Crystals, Verlag-Chemie, Wemhem, New York, 1978, ch 4, G W Gray and J W G Goodby, Liquid Crystals Textures and Structures, Leonard Hill, Glasgow, 1984, ch 1,3 13 C Noel, Recent Advances in Liquid Crystal Polymers, ed L L Chapoy, Elsevler, New York, 1985, ch 9 14 P J Alonso, M Marcos, J I Martmez, V M Orera, M L Sanjuan and J L Serrano, Liq Cryst, 1993,13,585 15 A Abragam and B Bleaney, Electron Paramagnetic Resonance of Transition Ions, Clarendon, Oxford, 1970, ch 7 16 J E Wertz and J R Bolton, Electron Paramagnetic Resonance, MacGraw-Hill, New York, 1972, ch 11 17 M P Eatsman, M Horng, B Freika and K W Shew, Liq Cryst, 1987,2,23 18 A Bencini and D Gatteschi, EPR of Exchange Coupled Systems, Spnnger, Berhn, 1990, ch 3 19 S H Glarum and J H Marshall, J Chem Phys, 1966,44,2884 20 S H Glarum and J H Marshall, J Chem Phys, 1967,46,55 21 P L Nordio and P Busohn, J Chem Phys ,1971,55,5485 22 P L Nordio, G Rigatti and U Segre, J Chem Phys, 1972,56,2117 23 C F Polnaszek, G V Bruno and J H Freed, J Chem Phys, 1973, 58,3185 Paper 5/02858B, Received 3rd May, 1995

ISSN:0959-9428    

DOI:10.1039/JM9960600533

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Molecular motions near the glass transition in diethylene glycol bis (ally1 carbonate) as studied by dielectric relaxation spectroscopy Ian K. Smith," Stuart R. Andrews,' Graham Williams"" and Paul A. Holmesb 'Department of Chemistry, University College of Swansea, Singleton Park, Swansea, UK, SA2 8PP bPilkington Technology Management Limited, Hall Lane, Lathom, Orrnskirk, Lancashire, UK L40 5 UF The monomer diethylene glycol bis(ally1 carbonate), used commercially to produce CR39 resin for optical lenses and safety apparatus, has been studied by dielectric relaxation spectroscopy in order to characterise fully the component dipolar relaxations. Various theoretical functions have been used to fit the dielectric relaxation spectra obtained above the glass transition temperature.The principal relaxation (a-process) which is associated with the main glass transition of the monomer arises from the co-operative motions of dipoles. It was found to behave in a non-Arrhenius manner, and indicates that at -95 "C and below the monomer behaves as a glass, at higher temperatures up to -60 "C it is a viscoelastic solid, and at temperatures above -60 "C the sample is a supercooled liquid. The origins of the dielectric a-relaxation process are discussed in terms of recent approaches including mode-mode coupling theory, models of dynamic heterogeneity and MD computer simulations. Cured polymers of diethylene glycol bis(ally1 carbonate), or CR39, are produced by a radical-initiated thermopolymeris- ation process.The polymer is important since it possesses a high optical clarity and impact resistance, making it useful for applications such as prescription optical lenses and for safety equipment. Many studies have been undertaken to investigate the extent of cure and the mechanical characteristics of the fully cured materials. Experimental methods used include titration of double bonds,' dilatometry,2 mid-range IR spec- tro~copy,~ Raman spec- solution-precipitation of p~lymer,~ tro~copy,~fracture testing6 and, recently, dielectric relaxation spectroscopy (DRS).',' Although these studies have been thor- ough in facilitating an understanding of the properties in the cured polymer system, only a DRS study' has given a basic insight into the dipole relaxation processes that occur in the uncured monomer, and how these might change with cure as the polymer material is formed.Motions of dipolar groups in these systems give rise to multiple dielectric relaxations which may be studied over wide ranges of frequency and temperature. In order to understand more fully these relaxation processes in the CR39 polymer, it is the aim of the present investigation to characterise fully the relaxation processes which occur within the monomer itself using DRS over a wide frequency and temperature domain. These processes can be understood in terms of relaxation phenomena in the glass transition (T,) range which arise from the micro-Brownian motions of the molecules and local motions of the dipoles. The structure of the CR39 monomer is shown in Fig.1. It is expected that the principal peak in the dielectric loss spectrum will be observed for the a-relaxation process (micro-Brownian motions of dipoles)' that gives rise to the glass transition of the material. The ester and ether groups in the molecule are dielectrically 0 'CH2-CH2-0-C-O-CH2-CH-CH2II active, yielding the r-process and, in addition, a b-relaxation process' due to the sub-% segmental motions of the carbonyl units. The dielectric data, presented as complex permittivity E*(w), can then be represented in terms of theoretical functions, from which comparison with other glass-forming liquids can be made in terms of the theoretically determined fit parameters associated with these functions.The spectral line-shape of permittivity E'(o) and loss factor E"(w)are determined over a wide range of frequency f(= co/27c) and temperature leading to the frequency-temperature locations of the a-and P-processes. Experimenta1 A sample of the pure monomer was provided by Akzo Chemicals, and was stored, when not in use, in a refrigerator below -10°C. At these temperatures the sample is a super- cooled liquid. Dielectric measurements were performed using a Solartron SI 1260 Schlumberger Impedance/Gain-phase Analyser with a Chelsea Dielectric Interface, enabling the ac frequency range 10-3-104 Hz to be covered with a high degree of precision. A full schematic representation of the measuring system is given in Fig. 2. Temperature control of the sample was achieved using a Novocontrol Quatro temperature con- troller unit that utilises a liquid-nitrogen cryostat system.This enabled heating and cooling of the sample using N, gas in the range -150 to 400°C with a precision of 0.1 C. The dielectric instrumentation and Quatro temperature controller system were controlled by a central computer that used the -I sample holder Fig. 1 Structure of diethylene glycol bis(ally1 carbonate) (CR39) monomer Fig. 2 General overview of the dielectric apparatus used J. Muter. Chem., 1996, 6(4), 539-546 539 Novocontrol ‘WinDETA’ software package WinDETA is a Windows-based software package that enables the user to set up and control a complete dielectric measurement automati- cally or interactively The sample holder consisted of two brass discs, the first was a cup-like disc (a flat circular disc of exterior diameter 40 mm, with a small raised edge to prevent sample spillage, and an inside diameter of 36 mm), which acted as the bottom sample electrode The second is a flat circular disc of diameter 30 mm which acted as the top sample electrode The top disc sat in the cup of the bottom disc, the two being separated from one another by two thin (120 pm) Teflon strips This electrode sample holder was then centred in the Novocontrol BDS1200 sample cell, and electrical contact was made to the brass discs via two circular brass electrodes forming part of the BDS1200 holder The BDS1200 discs consisted of a height-adjustable top disc of diameter 30 mm and a fixed bottom disc of diameter 40 mm diameter containing a small thermocouple that acted as the temperature sensor for the sample Tight adjustment of the BDS1200 top disc ensured good electrical contact between corresponding discs and sample The WinDETA software instructed the Solartron SI 1260 to measure the impedance of the parallel plate capacitor formed by the sample From this, the capacitance C and resistance R of the sample cell were obtained directly In order to calculate the dielectric constant E‘ and relative loss factor E” for a sample, the software used eqn (la) and (lb) E‘ =(cf-C,)/C0 + 1 (14 E” =G/coCo ( 1b) where Cf is the capacitance of the sample-filled capacitor, C, is the capacitance of the empty cell, co is the angular frequency (27cf)and C, is the active capacitance given by eqn (2) Co=AEO/d (2) where d is the perpendicular distance between the parallel electrodes, E~ is the permittivity of free space and A is the active area available to the sample given by the area of the top electrode less the area of the spacers Using the WinDETA software, frequencies of between 0 01 Hz and 10 kHz were measured for the sample CR39 monomer over the temperature range of -50 to -140°C This was sufficient to characterise fully the relaxation processes observed in the DRS experiment and to allow a good theoreti- cal analysis of the results Theoretical Considerations For a single relaxation time process, the dielectric relaxation time z is defined by eqn (3) 7 = 1Pdrnax (3) wheref,,, is the frequency at which the maximum loss occurs In practice, however, it is found that most systems do not have a single relaxation process and therefore we must define an average relaxation time, (z), given by eqn (4) (7) =1/2nfmax (4) Thus the average dipole mobility at a given temperature is measured by the frequency at which the maximum loss occurs A feature of glass-forming systems is that they exhibit common behaviour in the glass transition, or a-relaxation, range The a-relaxation process has a number of characteristic features The temperature dependence of the average relaxation time for this process is non-Arrhenius, unlike a /?-relaxation process which follows an Arrhenius relation [eqn (5)] (7) =To exp (%) where (z) is the average relaxation time given by eqn (4), zo is an empirically determined constant, Qapp is the apparent Arrhenius activation energy and R is the gas constant The Arrhenius relation has a linear relation of log fmaX vs 1/T whereas the a-relaxation process has an activation energy that increases with decreasing temperature This was first described by the empirical Vogel-Fulcher (VF) relation’ l1 [eqn (6)] wherez;, B and T,are empirically determined constants with typically lying 30-50 K below the experimentally determined apparent glass transition temperature The VF expression was put into a related form by Williams, Landel and Ferry (WLF)12 who recognised that this behaviour was common for a wide variety of materials [eqn (7)] (7) where T and & are the temperature and reference temperature, respectively, and C1 and C2 are empirically determined param- eters, given by B/(T -To)and (T-&), respectively The VF and WLF equations can then be used to calculate the apparent activation energy, Qapp, of the a-relaxation process at each sample temperature using eqn (8) (T>To) (8) This non-Arrhenius relation is curved with Qapp increasing with decreasing temperature and can be compared with the simple Arrhenius relation for broad secondary /?-relaxation processes, where (9) However, molecular glass-forming liquids all give a primary a-relaxation which appears to follow a non-Arrhenius function due to the cooperative nature of the relaxation process The complex permittivity &*(a) -~”(co)of a material =&’(a) can be expressed as eqn (10) using the Fourier-transform relation where 4(t) is a decay function for polarisation that describes the relaxation of a material following the step-removal of an electric field For many materials the approach to equilibrium following a small perturbation is non-exponential or ‘stretched exponential’ and for such materials #(t) can be expressed by the Kohlrausch-Williams-Watts (KWW) fun~tionl~-~’ [eqn (11)l The frequency dependence of the average relaxation time is based on the work by Williams and Watts14 l5 using analytical transformation of eqn (1 1) to the frequency domain according to eqn (10) When ff= 1, eqn (1 1) becomes the Debye equation which assumes a single relaxation time for all molecular species Havriliak and Negami16 have provided an expression to describe the broad asymmetric relaxation curves in the fre- quency domain [eqn (12)] 540 J Mater Chem, 1996, 6(4),539-546 where 2 and p are parameters that relate to the skew and broadness, respectively, of the implied distribution of relaxation times. Similarly to the KWW function [eqn.(ll)] the Havriliak-Negami (HN) function becomes the single relax- ation-time equation when the parameters a and /? are equal to 1. Williams and co-w~rkers~~,~~ have shown that the KWW function, using suitable values of can be used to fit, approxi- mately, the asymmetrical loss peaks in the frequency domain associated with the a-relaxation process of many glass-forming materials.They have obtained p values for the a-relaxation process of several glass-forming polymers with values ranging between 0.38 and 0.56.15,17,1sIt is expected that most glass- forming systems wzuld fall within this range. Further, they found values of /? for the dielectric a-process in viscous molecular liquids” to lie in the range 0.52-0.55. Numerical values of normalised real permittivity and loss factor as a function of oz have been tabulated by Koizumi and Kita.20 Utilising these tables, the KWW function can be used as a fitting function to data enabling values of p to be determined over a range of temperature for a particular system. Following the work by Williams and co-~orkers,~~-~~ many dielectric studies have been made with different polymeric and non-polymeric glass-forming systems, which have been reviewed extensively (see for example refs. 2 1-28 and references therein).These studies showed that the KWW function, although divergent from experimental data in the short time and/or high frequency regions, produced the shape of the asymmetric a-relaxation process successfully over a large part of the relaxation range. Results Fig. 3(a) and (b)show how the values of E’ and E” for the CR39 monomer vary with the frequency and temperature of measure- ment. Fig. 3(u) shows the decrease in E’ that occurs at frequen- cies in the range 10 mHz to 10kHz as the temperature is decreased.Fig. 3(b) shows the loss factor E” arising from both the ionic conductivity and the dielectric relaxation of the material. The ionic conductivity is seen in Fig. 3(b) as a rising loss at high temperatures and low frequencies. Above -50°C the dielectric loss values were dominated by ionic conduction losses. The loss peaks occur at increasingly higher frequencies as the temperature is raised and it is evident from Fig. 3(b) that the peak will occur at microwave frequencies at room temperature. The prominent dipole process in Fig. 3(a) and (b) is the a-process and is due to the large-scale micro-Brownian motions of the molecules. Fig. 3(c) enlarges the low-tempera- ture region in Fig. 3(b) and a small shoulder at the low- temperature (< -95 “C)side of the loss peak is seen to occur.This small, broad process is thought to be due to the localised segmental motions of the monomer dipoles which have been shown to be active in this temperature range for this7 and related materials.25 Fig. 4(u) and (b)show the behaviour of F’ and E”, respectively, as a function of temperature. Both figures show that as the frequency is decreased the region in which dielectric relaxation occurs, characterised by the decrease in E’ from high to low values and the corresponding loss curves in F”, shifts rapidly to lower temperatures. Fig. 4(a) shows that E’ falls in the relaxation range with a sharper decrease occurring at lower measuring frequencies.This is reflected in the corresponding loss curves in Fig.4(b) as a narrowing of the peaks as the measuring frequency is decreased, At 1kHz the loss curve reaches its maximum value at -72.5 “C, which compares favourably with the data of De Meuse7 who reported a loss peak at -78 “C for this frequency for the same monomer containing 3 mass% benzoyl peroxide. Fig. 5(u)and (b)show the behaviour of E’ and E”, respectively, as a function of frequency at temperatures in the range -70 to -90 “C. It can be seen that a decrease in temperature does w Fig. 3 Evolution of (a)the permittivity and (b)the loss for the monomer shown in three dimensions; (c) shows the loss for the sub-T, relaxation not alter appreciably the relaxation strength AE=E~- E, or the peak height of the loss curves.The main effect of a decrease in temperature is seen as a large shift of the dispersion region in E’ and the corresponding loss peak in E” to lower frequencies. These variations are due to the marked increase in (T) as the glass-transition temperature of the CR39 monomer is approached. Fig. 6 shows the plots of logfus. l/Tmax and logf,,, us. 1/T derived from Fig. 4(b) and 5(b),respectively. Here T,,, is the temperature of maximum loss for a measuring frequency f and fmax is the frequency of maximum loss for a sample temperature T. The loci of the two curves for the two representations are the same. The plot is curved, as expected for an a-process, showing that the apparent activation energy increases with decreasing temperature.As a consequence of this behaviour, the curve of Fig. 6 was fitted using the VF equation [eqn. (6)] and is shown as the solid line in Fig. 6. Table 1 gives the values of B, To and log(f,’= l/.r<) used for these fits. The quality of the fit shown in Fig. 6 is remarkable and shows that the VF equation gives an excellent representation of the frequency- temperature location of the a-process in CR39 monomer. We note that these data predict that the dielectric loss peak for this process occurs at 10l0Hz at 298 K, well above our measurement range. Our calculations show, based on the VF J. Muter. Chem., 1996, 6(4), 539-546 541 55r /a\ 50 45 w 40 35 30 -100 -90 -80 -70 -60 -50 -100 -90 -80 -70 -60 -50 TIT Fig.4 Dielectric spectra, measured at every decade of frequency in the range -2 <log( f/Hz) <4 for the monomer, showing (a) the permittivity and (b)the loss us temperature 0,-2 log(f/Hz) (curve on extreme left), A, 4 log(f/Hz) (curve on extreme right) 06 --05 04-b 03-02-01 -no-I.I*I.l.l~"' -2 1 0 1 2 3 4 log (f/Hz) Fig. 5 Evolution of (a)permittivity and (h)loss for the monomer with frequency at temperatures of -70°C (curve on extreme right) to -90 "C (curve on extreme left) at every 2 "C 48 49 50 51 52 53 54 55 lo3 KIT Fig. 6 Activation-energy plots for the monomer, showing non-Arrhenius behaviour for log fus l/Tmax(0)and log f,,, us 1/T(0)data Table 1 Parameters of the Vogel-Fulcher relation fitted to the tempera- ture and frequency domain of the dielectric a-relaxation process in CR39 monomer 147 4 1236 13 09 fit in Fig 6 and eqn (8), that Qappincreases from 140 kJ mol-' at 203 1 K to 265 kJ mol-' at 183 1 K Clearly Qappcannot be interpreted as being a true activation energy barrier for the reorientational motions of the dipoles, since these values approach those for the dissociation of chemical bonds It is more reasonable to relate the variation offmax with temperature to relaxation models involving the configurational entropy of the relaxing system As temperature is reduced towards the configurational entropy decreases markedly and this leads to a marked increase in the structural relaxation time in accord- ance with VF behaviour, as has been described in the relaxation model of Adam and Gibb~~~ and has been further discussed by Wong and Ange1125 and Matsuoka 30 Shape of the Relaxation Curves Fig 7 shows the experimental dielectric loss spectra for the CR39 monomer at four temperatures The data are fitted using the HN function [eqn (12)], and are represented as the unbroken lines in Fig 7 The values of a and p thus determined are given in Table2 It can be seen that the HN function describes the experimental data very well over most of the loss peak (4 decades of frequency) but predicts lower losses at higher frequencies than those observed This is possibly due to an additional higher-frequency dielectric process being 07r 02 01 00 -2 -1 0 1 2 3 4 log (f/Hz) Fig.7 Havriliak-Negami analysis of the loss of CR39 monomer at -80 (O),-82 (H),-84 (0)and -86 "C (0)The fitted HN functions are plotted as unbroken lines 542 J Muter Chem, 1996, 6(4),539-546 Table2 Parameters of the HN and KWW functions fitted to the experimental data for the CR39 monomer Havriliak-Negami fit KWW fit T/"C a P P -76 --0.55 -78 --0.55 -80 0.435 0.894 0.55 -82 0.434 0.895 0.56 -84 0.435 0.895 0.56 -86 0.435 0.895 0.56 -90 --0.56 present at the lower temperatures of measurement, due to the secondary sub-glass transition process described above, associ- ated with the local dipole motions of the monomer.Table 2 shows that over the temperature range studied, the a parameter, which is associated with the skew of the loss peak, and the p parameter, associated with broadness of the loss peak, remain approximately constant, showing that the shape of the relax- ation function is hardly changing with temperature over the range shown in Fig.7. The permittivity and loss curves of Fig. 5(a) and (b) were also fitted using the KWW function [eqn. (1l)]. For a single relaxation time process we may write: A logf= 1.14 (13) where A logf is the full half-width of the loss curve in a plot of E" us. log6 Curves that do not obey the single relaxation time model are broader by comparison and we may write as an approximation for the KWW function the relati~n:'~ Dz 1.20/A log f (14) where pis the KWW parameter introduced above.The curves illustrated in Fig. 5(b) all have A logfz2.0, thus we expect gz0.6. Using this value as an indicator, the tables of Koizumi and Kita2' were used to fit the KWW function to the E' dispersion curves and associated loss curves shown in Fig. 5(a) and (b). Fig. 8 shows representative fits to the loss data in the range -80 to -86 "C. Similar plots were also obtained for all temperatures studied and the results of this analysis are included in Table 2. For each loss curve, at each temperature, the KWW function was found to fit the data very well at the lower frequencies but fell slightly below the E' dispersion and E" loss curves at the higher frequencies. This behaviour has been found to be common to the dielectric a-relaxation of many other small-molecule glass-forming systems as reviewed by Williams.21 Again the difference may be due to a higher- frequency process being present as indicated above.Never- theless the KWW function proves a reasonable fit to the data 0.7r 0.6 0.5 0.4 w 0.3 0.2 0.1 0.0 I.I.1.I.I.I -2 -1 0 1 2 3 4 log (I/Hz) Fig. 8 KWW analysis of the loss of CR39 monomer at -80 (0),-82 (m), -84 (0)and -86 "C (0).The fitted KWW functions are plotted as unbroken lines over most of the loss peak (3 decades of frequency) and we can describe the relaxation of the CR39 monomer as being non-exponential or stretched-exponential following a pertur- bation by an ac field. Discussion It is well known that the dielectric a-relaxation in small- molecule glass-forming liquids is characterised by (i) broad dielectric dispersion and absorption features that conform, approximately, to HN, KWW or Davidson-Cole28 functions and (ii) an average relaxation time that follows, approximately, the Vogel-Fulcher relation [eqn.(6)]. Our comprehensive dielectric data for the CR39 monomer shows that this glass- forming liquid follows this pattern of behaviour and exhibits model behaviour for such a liquid. We have seen that (z) obeys, with good accuracy, the VF equation in the range studied above Tgin which the fictive temperature Tf25.26*31and the actual temperature T of the sample are equal. If measure- ments were performed in and below the glass transition region the non-equilibrium effects would become apparent since T+ Tf and the VF equation would not be obeyed.The temperature T,, which for our data for the CR39 monomer is 145.2K, is interpreted to be the temperature at which the configurational entropy S, of a material in its equilibrium state would approach zero.25 Since T,< this cannot be achieved in practice so T, is anticipated (premonitory behaviour) from our measurements on the system in equilibrium above Tg. The theory of Adam and Gibb~~~ (see also ref. 30) makes the assumption that (z) and S, are related, and this leads to the VF equation under certain circumstance^.^'^^^-^^ However, it should be pointed out that (z) is a transport coeficient, being an integral, over time, of a time-correlation function CJt) for the reorientational motions of dipole^,^^,^^,'^ while S, is an equilibrium thermo- dynamic quantity that has no obvious connection to the time- scale of dynamic events.While it is plausible to relate (z) to S, it is not evident that a dynamic property and an equilibrium property for a stationary thermodynamic system have to be related in this way. We note that To may be estimated using equilibrium statistical mechanics for a dense system of polymer chains, as was shown originally by Gibbs and diMar~io~~ (see also ref. 35). The spectral line-shape for the dielectric a-process in the CR39 monomer is seen to be fairly well represented by the KWW function over about four decades of frequency (see Fig. S), but lower values than those observed experimentally in the higher frequency range are predicted.The value of p (ca. 0.55) used to obtain these fits is the same as that found for the a-process in the glass forming liquid 0-terphenyl and solutions of dipolar solutes in that solvent,21. 36-39 de spite the different chemical structures of the CR39 monomer and o-terphenyl. Comparison of the fit of the a-relaxation loss curve for anthronelo-terphenyl (Fig. 7 in ref. 39) with the fits shown in Fig. 8 for the present material shows that the excess absorp- tion at high frequencies over that calculated from the KWW function is far higher for the CR39 monomer than it is for the anthronelo-terphenyl solution. This suggests that in the present material, local motions, primarily for the ether groups, occur prior to the main a-process and to a larger spatial extent than local motions of anthrone or o-terphenyl molecules.The HN function, with two adjustable shape parameters, provides a better fit to the data (see Fig. 7). The form of the spectral line shape of the dielectric a-process in small-molecule glass-forming liquids has been considered recently by Wu et aL4' who have proposed an empirical scaling law to reduce loss data, in the frequency domain, to normalised master curves. The applicability of this scaling law4' has been critically e~arnined.~'-~' In parallel, Gotze and co-~orkers~~-~~ have proposed a mode-mode coupling theory for relaxation in glass-forming liquids that embraces the primary (a) and J.Muter. Chem., 1996, 6(4),539-546 543 further (short-time) relaxation processes. In our case an additional absorption peak at short-time/high frequencies to the primary a-process is predicted, which we term a P-process. These processes in the mode-mode coupling theory follow from the assumption that there is a second-order memory function that takes on an assumed form which is a function of the time-correlation function being elucidated within the Such theories take no account of the kind of molecular motion being studied, which for dielectric relaxation is the reorientational motions of dipoles expressed by the time- correlation functi~n~~?~~ [eqn. ( 15)]: C(CLl(O).PJ(t)) C,(t)= (15)l,’ C(P*(O).PJ(O)> l.3 where the sum extends over all dipoles contained in a macro- scopic volume V.For the CR39 monomer, both ester and ether dipoles are involved in the sum and we note that eqn.(15) contains auto- and cross-correlation functions (both dynamic and equilibrium). Thus the memory function approach that is explicit in the mode-mode coupling theories is interesting for application to our data but requires that such memory func- tions actually exist physically for reorientational motions of dipoles in viscous molecular liquids. As we have discussed re~ently’~,~~a weighted sum of parallel processes each having no memory can be expressed in terms of virtual memory functions that have no physical significance. An alternative approach to the a-relaxation in glass-forming liquids and amorphous polymers is that of Schmidt-Rohr and Spie~s’’-’~ who have demonstrated, using multi-nuclear multi- dimensional NMR studies of the a-relaxation in amorphous poly(viny1 acetate) and poly(styrene), that these systems behave as if there were present a ‘dynamic heterogeneity’ of the moving units (chain segments for polymers).Starting at an arbitrary time t=O, an ensemble appears to comprise units finding themselves in different local states. As time progresses, units in fairly free environments reorientate quickly and partially relax the ensemble while at the other extreme units in con- strained environments hardly relax in the time-scale of the reorientation of the ‘free’ units. As a result of the broad range of environments (states) occurring at t =0, a broad relaxation function emerges for the motions of the ensemble, as a weighted sum of essentially parallel independent processes, within the total time-scale for the p-and overall a-relaxations, giving a KWW- or HN-type relaxation for the a-proce~s.’~-~~ Such a dynamic heterogeneity appears to be the source of the broad a-relaxations observed by Schmidt-Rohr and Spiess in their NMR experiments.Further experiments” showed that contin- ual exchanges occur between the local states experienced by a representative group, hence ensuring the system is ergodic, i.e. time-averaged and spatially averaged time-correlation func- tions of the motion are identical,33 and thus units behave on average in an equivalent manner in their dynamic properties.Memory functions do not appear to be involved necessarily in such an overall relaxation process. In parallel with these, Ediger et u1.60-64have used fluorescence methods and angular- dependent photoselection in optical bleaching to monitor the a-process of dyes in o-terphenyl. Their studies suggest strongly that the broad a-relaxation (KWW- or HN-type) arises from dynamic heterogeneity, as described above. Further dielectric experiments by Bohmer et uL6’ involving special pulse sequences and non-linear ‘hole-burning’ with large E fields of the dipole orientation-distribution in glass-forming liquids such as propylene carbonate and glycerol yield results for the dielectric a-relaxation that are consistent with a model of dynamic heterogeneity that is intrinsic to the amorphous state and is general for glass-forming liquids.As a result of these complementary st~dies’~-~~ we consider 544 J. Muter. Chem., 1996, 6(4), 539-546 that the dieletric a-relaxation for the CR39 monomer may be given by a weighted sum of individual reorientational processes each with its own relaxation function which is obtained by averaging over all trajectories in time for a given initial state for a reference dipole. The autocorrelation function for the motion of a reference dipole z is then given by eqn. (16): whereA(E)dE is the probability of obtaining the dipole i in the range of environments (in configuration space) between s” and (s”+ dE).Hence [(pL(O).pl(t))=]is the correlation function for a dipole that is initially in environment E and reorients in time through a range of trajectories. ()= indicates the average taken over all those trajectories starting in configuration Z. In its simplest form the terms [(pl(0).p,(t)),-] in eqn. (16) each have a single exponential decay with relaxation time z(E)so [(pl(0).pt(t))] involves a simple distribution of relaxation times with a distribution function A(..”), i.e. a simple weighted sum of parallel processes where each process has a single exponential decay in time. Such a description is precisely that used from the earliest descriptions of broad relaxation pro- cesses in polymers as reviewed by Ferry66 and McCrum et ~1.~’ However, it is entirely possible that [(pl(0).pL(t))=]is not a single exponential decay function.For example, it may contain a short-time part (p-process) and a long-time part (a-process) and their relative magnitudes, their individual relaxation times and their functional forms may vary with S. This will be the general situation and its internal structure is not easily investi- gated experimentally. A reasonable model for glass-forming liquids is that the fast components in [(pl(0).pl(t))Z]are similar in time-scale for all initial configurations (partial relax- ation of dipoles, P-process) but the slow components that contribute to the overall a-process, vary markedly with E. This results in a fast process (p)and a slow process (a) where the latter is a weighted sum over a broad distribution, f(E), involving individual relaxation times z(E).For the CR39 monomer, the secondary (p)process appears to be far smaller than the a-process. However, as we have indicated above, the ‘excess absorption’ for the a-process at high frequencies over that calculated using the KWW or HN functions makes us suggest limited motions of dipoles (mainly ether dipoles) par- tially relax [(pl(0).pt(t))3]at short times, but do not provide necessarily a distinct /I-process. We note that the loss curves for the CR39 monomer and for related glass-forming liquids2’ having pz0.55 (or HN ~1~0.42,pz0.91) are indicative of dynamic heterogeneity at the mesoscopic level in molecular liquids. It is possible to increase the coarseness of the heterogeneity by forming mix- tures of glass-forming liquids or of amorphous polymers.For example, Shears and Williams37 examined the dielectric a- relaxation in homogeneous (optically transparent) mixtures of (polar) di-n-butylphthalate (DBP) with (non-polar) o-terphenyl and found that the half-width of the a-loss curve increased from 2.0 to 2.5 on going from 0 to 30% DBP and then decreased monotonically to 1.8 for 100% DBP. This was strong evidence for heterogeneity of a dynamic kind, on a wavelength scale shorter than visible light in which o-terphenyl- rich regions relax slowly and DBP-rich regions relax quickly, compared with the average dielectric relaxation time for the mixture. The concentration fluctuations in o-terphenyllDBP mixtures occur on a time-scale shorter than that for dielectric relaxation of the individual molecules, so a weighted sum of relaxations, each of KWW-type weighted over the distribution of local concentrations of DBP molecules, contributes to the overall relaxation of the mixture.Ergodicity is maintained in such a system through the slow evolution of concentration fluctuations throughout the liquid. Thus the line shape for the loss factor for a pure glass-forming liquid (as in Fig. 7) is a limiting one based on fluctuations in local environments (ie dynamic heterogeneity that is intrinsic to such a liquid) While we have rationalised our data for the CR39 monomer in terms of the dynamic heterogeneity model, we note that real-time simulations of molecular dynamics have been made for realistic models for o-ter~henyl~~ and molten bulk poly- ethylene 69 Thus Lewis and Wahn~trom~~ showed that o-terphenyl molecules exhibited ‘libration’, ‘floppy librations’ plus ‘excursions from equilibrium’, ‘Jump motions’ and ‘very floppy diffusion’, on different time-scales during molecular reorientations Roe6869 showed that the correlation functions (P,[cos O(t)]) (where 1= 1,2,3 n, P indicates the Legendre 17 18 19 20 21 22 23 24 G Williams and D C Watts, in Dielectric Properties of Polymers, ed F E Karasz, Plenum, New York, 1971 G Williams, M Cook and P J Hains, J Chem SOC Faraday Trans 2,1972,68,1045 G Williams, J Non-Cryst Solids, 1991,131, 1 N Koizumi and Y Kita, Bull Inst Chem Res Kyoto Univ, 1978, 56,300 G Williams, in Dielectric and Related Molecular Processes, ed M Davies, Specialist Periodical Report, The Chemical Society, London, 1975, vol 1, p 151 G Williams, IEEE Trans Electr Insul, 1985, E1-20, 843 Relaxations in Complex Systems, ed K L Nargai and G B Wright, US Government Printing Office, Washington DC, 1985 K L Ngai, R W Rendall, A K Rajagopal and S Teitler Ann N Y polynomial and O(t) is the orientation of a bond vector at time t) contain a short-time part (local partial motions, 0 01-10 ps) and a longer-time a-process that is described by a KWW function with /3 =0 56 & 0 04 Thus this MD simulation for the molecular dynamics of an amorphous bulk polymer predicts behaviour of the kind observed for the CR39 monomer, which 25 26 27 28 Acad Sci , 1987,484,150 J Wong and C A Angell, Glass Structure by Spectroscopy, Marcel Dekker, New York, 1976 C T Moynihan et al, Ann NYAcad Sci, 1976,279,15 J M Pochan, H W Gibson, M F Froix and D F Hinman, Macromolecules, 1978, 11, 165 N G McCrum, B E Read and G Williams, Anelastic and emphasises the similarity in the a-relaxation for amorphous polymers and glass-forming liquids as discussed by us pre- vlous~y17 19 21 36 39 Stretched exponential behaviour is ubiqui- tous for the a-relaxation in amorphous systems as observed by different techniques 70 71 29 30 31 Dielectric EfSects in Polymer Solids, Dover Publications , New York, 1991 G Adam and J A Gibbs, J Chem Phys, 1965,43,139 S Matsuoka, Relaxation Phenomena in Polymers, Oxford University Press, New York, 1992 I M Hodge, J Non-Cryst Solids 1994,169,211 32 G Williams, Chem Rev 1972,72, 55 Conclusions 33 34 G Williams, Chem SOC Rev 1978,7,89 J H Gibbs and E A Di Marzio, J Chem Phys 1958,28,373 The dielectric a-relaxation in the CR39 monomer has been studied over ranges of frequency and temperature and is shown 35 36 37 G Williams, Trans Faraday SOC 1963,59,1397 G Williams and P J Hains, Chem Phys Lett 1971,10, 585 M F Shears and G Williams, J Chem SOC Faradav Trans 2 to be well represented by the Vogel-Fulcher equation (for average relaxation time) and fairly well represented by the KWW and HN functions (for spectral line-shape) The behav- lour is rationalised in terms of the dynamic heterogeneity model proposed originally by Schmidt-Rohr and Spiess and it appears that the dipole moment correlation function contains internal structure involving equilibrium and dynamic quantities that may only be further elucidated using techniques that give spatial information on the overall a-process The importance of such work in providing an understanding of the physical properties of the CR39 monomer and other glass-forming liquids that have widespread applications in their own right or as precursors to optically transparent glasses is self-evident 38 39 40 41 42 43 44 45 1973,69,608 M F Shears and G Williams, J Chem SOC Faraday Trans 2 1973,69,1050 G Williams and P J Hains, Faraday Symp Chem SOC 1972,6,14 L Wu, P K Dixon, S R Nagel, B D Williams and J P Carini, J Non Cryst Solids 1994,131-133,32 A Schonhals, F Kremer and E Schlosser, Phys Rev Lett 1991, 67,999 A Schonhals, F Kremer and E Schlosser, Phys Rev Lett 1993, 71,4096 F Stickel, F Kremer and E W Fischer, Physica A 1993,201,318 A Hoffman, F Kremer and E W Fischer, Physica A 1993, 201, 106 F Stickel, E W Fischer, A Schonhals and F Kremer, Phys Rev Lett 1994,73,2936 46 W Gotze and L Sjogren, Rep Prog Phys 1992,55,241 We thank the Materials Committee of the SERC for a grant for the purchase of the Novocontrol dielectric spectrometer and for the award of post-doctoral research assistance to S A The EPSRC is thanked for a CASE award to I K S We also 47 48 49 W Gotze and L Sjogren, J Phys C Solid State Phys 1987, 20,879 W Gotze, in Amorphous and Liquid Materials ed G Fritsch and G Jacucci, Matinus Nijhof, Dordrecht, 1987, p 34 W Gotze, in Liquids Freezing and the Glass Transition ed thank Mr Tony Aldridge for his technical assistance D Levesque, J P Hansen and J Zimm-Justin, Elsevier, New York, 1991 50 L Sjogren and W Gotze, in Dynamics of Disorded Materials, References ed D Richter, A J Dianox, W Perry and J Teixeira, Springer, Berlin, 1989, p 18 1 2 3 4 5 6 7 8 9 10 W R Dial, W E Bissinger, B J De With and F Strain, Ind Eng Chem, 1955,47,2447 E Schmarr and K E Russell, J Polym Sci Polym Chem Ed, 1980,18,913 T Portwood and J Stejny, Nuclear Tracks, 1986,12,113 V S Nikiforenko, N N Alekseyev and Y S Zaitsev, Polym Sci USSR (Engl Trans1 ), 1986,28,2290 J H O’Donnell and P W OSullivan, Polym Bull, 1981,5, 103 M Frounchi, R P ChaFlin and R P Burford, Polymer, 1994, 35,752 M T De Meuse, Polym Eng Sci , 1993,33, 1049 M T De Meuse, J Polym Sci Polym Phys Ed, 1994,32,1749 G Williams, Adv Polym Sci , 1979,33, 59 H Vogel, Physik Z , 1921,22,645 51 52 53 54 55 56 57 58 W Gotze, in Liq Crist Trans Vitreuse Les houches ed J P Hansen, D Levesque and J Zimm-Justin, North Holland, Amsterdam, 1989,p 287 W Gotze and L Sjogren, J Non-Cryst Solids 1991,131-133,161 L Sjogren and W Gotze, J Non-Cryst Solids 1994,172-174,7 W Gotze and L Sjogren, J Non-Cryst Solids 1994,172-174,16 G Williams, in Keynote Lectures in Selected Topics In Polymer Science, ed E Riande, Instituto de Cientas y Technologia de Polimeros, 1995 G Williams and J Fournier, J Chem Phys 1996, in press K Schmidt-Rohr and H W Spiess, Phys Rev Lett 1991, 66, 3020 J Leisen, K Schmidt-Rohr and H W Spiess, J Non-Cryst Solids 1994,172-174,737 11 G A Fulcher, J Am Ceram SOC, 1925,8,339 59 K Schmidt-Rohr and H W Spiess, Multi-dimensional Solid State 12 M L Williams, R F Landel and J D Ferry, J Am Chem SOC, NMR and Polymers Academic Press, London, 1994 1955,77,3701 60 M T Cicerone, F R Blackburn and M D Ediger, J Chem Phys 13 R Kohlrausch, Pogg Ann Phys, 1854,4,56,77 1995,102,471 14 G Williams and D C Watts, Trans Faraday Soc , 1970,66,80 61 M T Cicerone, F R Blackburn and M D Ediger, J Chem Phys 15 G Williams, D C Watts, S B Dev and A M North, Trans 1992,97,2156 16 Faraday SOC, 1971,67,1323 S Havnliak and S Negami, J Polym Sci Part C, 1966,14,99 62 D A Waldron, M D Ediger, Y Yamaguchi, Y Matsushita and I Noda, Macromolecules, 1991,24, 3147 J Muter Chem, 1996,6(4), 539-546 545 63 T Inoue, M T Cicerone and M D Ediger, Macromolecules, 1995, 28,3425 64 M T Cicerone and M D Ediger, J Chem Phys, submitted 65 R Bohmer, A Loide and R Chamberlain, personal communication 66 J D Ferry, Viscoelastic Properties of Polymers, Wiley, New York, 1970,2nd edn 67 L J Lewis and G Wahnstrom, J Non-Cryst Solids, 1994, 172-174,69 68 R J Roe, J Non-Cryst Solids, 1994,172-174,77 69 R J Roe, J Chem Phys, 1994,100,1610 70 Proceedings of the International Discussion meeting on Relaxations in Complex Systems, Parts I and 11, ed K L Ngai and G B Wright, J Non-Cryst Solids, 1991, p 131 71 Proceedings of the Second International Discussion meeting on Relaxations in Complex Systems, Parts I and 11, ed K L Ngai and G B Wnght, J Non-Cryst Solids, 1994, p 172 Paper 5/07011B, Received 24th October, 1995 546 J Muter Chem, 1996, 6(4), 539-546

ISSN:0959-9428    

DOI:10.1039/JM9960600539

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Structure, dielectric relaxation and electrical conductivity of 2,3,7,8-tetramethoxychalcogenanthrene-2,3-dichloro-5,6-dicyano=l,4-benzoquinone1 :1 charge-transfer complexes? Ulrich Behrens,' Ricardo Diaz Calleja,*b Mark Dotze,b Ursula Franke,' Walter GunDer,' Gunter Klar,*" Jens Kudnig," Falk Olbrich," Enrique Sanchez Martinez,d Maria J. Sanchisb and Barbel Zimmer' "Institut fur Anorganische und Angewandte Chemie der Universitat Hamburg, Martin-Luther-King-Platz 6, 0-201 46 Hamburg, Germany Departamento de Termodinhmica Aplicada, E. T.S.I.I., Universidad Politkcnica de Valencia, Camino de Vera, s/n, E-46071 Valencia, Spain 'Institut fur Physikalische Chemie der Universitat Hamburg, Bundesstraj'e 45, 0-20146 Hamburg, Germany Departamento de Ingenieria Electrbnica, E.T.S.I.T., Universidad Politkcnica de Valencia, Camino de Vera, s/n, E-46071 Valencia, Spain ( 5,10-chalcogena-cyclo-diveratrylenes,2,3,7,8-Tetramethoxychalcogenanthrenes 'Vn2E2', E = S, Se) form isotypical 1 : 1 charge-transfer (CT) complexes with 2,3-dichloro-5,6-dicyano-174-benzoquinone (DDQ). X-ray analysis of Vn, S2-DDQ shows the compound to have a columnar structure with segregated stacks of donors and acceptors. The donors are virtually planar in accordance with a formulation of [VnzE2] '[DDQ] -. Donor cations and acceptor anions are equidistant in their respective stacks, but in each case they inclined to the stacking axis, nevertheless guaranteeing an optimum overlap of the half-filled frontier orbitals which are of n-type character according to MNDO calculations.Dielectric ac measurements of permittivity E' and loss factor E" clearly reveal two processes, a dielectric one at low temperatures and a conductive one at high temperatures. The dielectric process can be described by the Havriliak-Negami (HN) and the Kohlrausch-Williams-Watts (KWW) model, and the conductive process by a Debye-type plot. Using these methods, the relevant parameters are evaluated. The dc conductivities of polycrystalline samples moulded at lo8 Pa show a temperature dependence in the plots of In t~ us. T-l, which is typical of semiconductors. Two slopes are found; that in the low-temperature region (<285 K) is explained by an easy-path model (intragrain conductivity with low activation energies), whereas in the high-temperature region conduction across the grain boundaries (with higher activation energies) is becoming predominant.The activation energies for the intrinsic conductivities obtained by the ac and dc measurements are similar. Despite the columnar structure with segregated stacks, due to stoichiometric oxidation states of the components, the absolute values of conductivity are low (ca. S cm-' at 293 K), though higher (by a factor of ca. lo3)than those of compounds like Vn,E, * TCNQ with stacks in which donor and acceptor molecules alternate. The electron-rich 2,3,7,8-tetramethoxychalcogenanthrenes ( 5,lO-dichalcogena-cyclo-diveratrylenes, 'Vn, E2'; E = S, Se) act as donors in charge-transfer (CT) complexes. With tetra- cyanoethane (TCNE) the complexes 2Vn,Ez * TCNE are formed which in their solid states possess stacks of Vn,E, I TCNE I Vn, E, units., With 7,7,8,8-tetracyanoquinodi-methane (TCNQ), 1 : 1 complexes are obtained in the stacks in which donor and acceptor molecules alternate.3 As a conse- quence of their crystral structures both types of compounds show only poor electrical cond~ctivity.~*~*~ Using 2,3-dicyano-5,6-dichloro-1,4-benzoquinone(DDQ), complexes are formed which are isotypical for E = S and E = Se according to scanning electron microscope (SEM) measure- menk6 The dark blue compounds were easily prepared by combining the hot solutions in acetonitrile.In the case of the sulfur compound, single crystals suitable for a crystal structure determination could also be obtained.Crystal Structure Determination of Vn2S2 DDQ A Siemens P4 four-circle diffractometer (Mo-Ka radiation with II = 71.073 pm, 03-20 scan mode, Lorentz and polarization corrections) and the program Siemens SHELXTL-PLUS (VMS)7 were used for X-ray analysis. The structure was determined by direct methods. Fourier syntheses allowed the positions of all non-hydrogen atoms to be determined; these ?Part 7 of a series entitled Self-stacking Systems. For Part 6, see ref. 1. OaEnO0 E 0 I I H3C CH3 Vn2E2(E = S,Se) NCYCN 0 atom positions were refined with anisotropic temperature factors. The positions of the hydrogen atoms were calculated with fixed distances of 105 pm and isotropic temperature factors.The results are given in Tables 1 and 2.1 Descriptionof the structure Molecular structure. The asymmetric unit of Vn,S2 DDQ contains half a molecule of each component, the molecular $Supplementary data available from the Cambridge Crystallographic Data Centre: see Information for Authors, J. Muter. Chem., 1996, Issue 1. J. Muter. Chem., 1996, 6(4), 547-553 547 Table 1 Crystal structure parameters of Vn,S, * DDQ empirical formula c16 H1604 sZ * c8 c12 N2 OZ crystal system monoclinic space group p2/C alpm 370 8(2) blpm 1306 9(6) clpm 2355 7( 11) fljdegrees 93 50(4) z 2 Mlg mol-' 563 4 V/m3 1139 x lo6 Dlgcy 1 642 Plcm 5 16 scan range/degrees 5 < 28 < 50 independent reflections 2037 reflections with I F,I 2 44 1 Fol) 1548 refined parameters 165 R 0 0473 Rw 0 0436 Table 2 Atomic parameters of Vn,S, * DDQ 0 3579(4) 0 5294( 1) 0 4307( 1) 0 4485 (11) 0 4088(2) 04581(1) 0 5774( 11) 0 3853(2) 0 5138( 1) 0 6589(10) 0 2839(3) 0 5287( 1) 0 6126(9) 0 2072( 3) 0 4892( 1) 0 4765( 10) 0 2307(2) 0 4327( 1) 0 3924( 10) 0 3298 (2) 0 4181( 1) 0 6890( 7) 0 1078(2) 0 4991( 1) 0 8389(11) 0 0823( 3) 0 5550(1) 0 4368( 7) 0 1496( 2) 0 3968( 1) 02780(11) 0 1699( 3) 0 3410( 1) 0 2668(3) 0 9085( 1) 0 1914( 1) 0 2658( 10) 0 7019(3) 0 1969(1) 0 3949(9) 0 7968 (2) 0 2251( 1) 0 3878(10) 06091(2) 0 2254( 2) 0 0632( 7) 0 7022( 2) 0 1533( 1) 0 2696(10) 0 5141(3) 0 2005(1) 0 1723(9) 0 4370( 2) 0 1821(1) structures of which are shown in Fig 1 The outstanding feature of the donor is its planarity, although the thermal parameters of the sulfur atoms indicate that they may be disordered with deviations of up to +20 pm from the best planes of the two aryl rings From this a formulation for the +complex of [Vn, S,] [DDQ] -is suggested Namely, whereas the neutral Vn,S2 molecule is folded at the SS axis [angle of fold (defined as the angle between the normals to the best Q Fig. 1 Molecular structures of the components of Vn,S, -DDQ with atom numbering scheme 548 J Muter Chem, 1996, 6(4), 547-553 Table 3 Mean values of bond lengths (pm) and angles (degrees) in the donor molecule of Vn,S, -DDQ and comparable compounds Vn,S, * DDQ [Vn, S,] + [SbCl,] a Vn, Szb s-c 0-C (ar) 0-C (alk) C(S)-C(S) C(S)--C(H) CW-(30) C(O)-C(O)c-s-cc-0-c s-C(S)- C( S) S -C(S)-C( H) 0-c(0)-C(0) 172 6( 3) 135 2(4) 143 4(4) 140 3(5) 140 3( 5) 137 l(4) 142 8(5) 107O( 2) 116 8(3) 126 3(3) 113 9(2) 115 5(3) 172 3(5) 1349(5) 143 3(5) 139 5(6) 140 O(6) 136 2(6) 143 O( 7) 107 4( 3) 118 O(4) 126 O(4) 114 9(4) 114 5( 5) 177 6( 7) 136 9(8) 142 5( 9) 138 2( 10) 139 7(9) 138 O( 10) 141O( 10) 100 2( 3) 117 6( 5) 121 l(5) 119 O( 5) 115 2(6) 0-C(0)-C(H) C(S)-c(S)-C(0) C(S)-C( H)-C(0) C(H)-C(0)-C (0) 124 7( 3) 119 7(3) 120 4( 3) 119 9( 3) 125 9(5) 119 5(4) 120 O( 5) 119 6(5) 125 2(6) 119 8(6) 120 5(6) 119 6( 6) "Ref 10 bRef 8 planes of the aryl rings), 4 = 131 and 128" for the monoclinic' and orthorhombic' forms, respectively], its monocation [Vn,S,]+ is planar (4 = 180°)10 and any partially oxidized form [Vn2S2Ix+ (0 < x < l), e g 2Vn,S, -TCNE or Vn,S2 TCNQ, has angles between these values These observations correlate well with the oxidation potentials, El, of these acceptors (+0 51 V for DDQ, +0 15 V for TCNE and l2+O 17 V for TCNQ, each vs SCE) In the levelling of the donor molecule the methoxy substitu- ents are included, ze each pair of ortho-standing methoxy groups is coplanar with its aryl ring, both in exo positions, thus facilitating the formation of stacks in the crystal For other derivatives of Vn,S2 this behaviour has also been found,, the consequences with respect to bond lengths and angles have already been discussed in connection with the structure of Vn,S2 itself' (Table 3) A charge transfer will affect the bond lengths and angles of both the donor and the acceptor molecules Indeed, the data of Tables 3 and 4 confirm the formulation of the complex as [Vn,S,]+[DDQ]-since they agree well with those of the corresponding radical ions and differ significantly from those of the neutral molecules This is shown for the donor by the CS and CO distances and the angles in the central dithiin ring, for the acceptor by the CO distance and the beginning of equalization of the distances within the six-membered ring Crystal structure.From the unit cell of Vn,S,.DDQ in Fig 2 it can be seen that a columnar structure with segregated stacks of donor and acceptor radical ions is formed in the crystal The constituents of each stack are coplanar and equidistant, their molecular planes being inclined to the stack- ing axes (Fig 3) The inclination differs in the donor and acceptor columns, thus leading to different interplanar dis- tances, namely 359 and 308 pm for the donor and acceptor stacks, respectively, both distances being shorter than the van der Waals distance (half thickness of an aromatic nucleus, 185 prnI5) In the crystals of [Vn, S,] [SbCl,] * CH, CN'' the radical cations [Vn,S2]+, which are also planar, form different kinds of stacks There are two orientations of the coplanar ions in an alternating sequence ABAB (angle between the molecu- lar axes, 35") The interplanar distance (353 pm) agrees well with that in Vn,S2 DDQ Molecular Orbital (MO) Calculations In order to arrive at a better understanding of the CT interactions in Vn,S, -DDQ, MO calculations were carried out As shown already,I6 good results can be obtained by Table 4 Mean values of bond lengths (pm) and angles (degrees) in the acceptor molecule of Vn,S, -DDQ and comparable compounds Vn, S, -DDQ [NEtJ+[DDQ]-a DDQ~ c-Clc-0 171.5(3) 123.6(4) C-N C-C(N) C( CN)- C(CN) C( CN)- C(0) N-C-C C( Cl) -C( C1) c(C1) -c(0) cl-c-c(cl)c1-c-C(0) 0-c-C(C1) 114.7( 5) 143.0( 5) 136.8( 6) 138.6( 7) 147.2( 5) 144.5( 5) 178.0( 4) 121.6( 1) 115.8(2) 122.5( 3) 0-C-C(CN) C( N)-C- C( CN) C(N) -C-C(0) C (C1)- C( 0)-C( CN) C(C1)-C(CN)-C(CN) C( C1)- C( C1) -C(0) 123.0( 3) 119.7(2) 11 7.4( 3) 122.6 (2) 114.5( 3) 122.9( 2) "Ref.13. bRef.14. , f i(I b Fig. 2 Unit cell of Vn,S, * DDQ HAM317*'s calculations, whereas the MND019?,' method nor- mally gives less reliable values for unoccupied orbital^,^'-^^ i.e. too high energy differences between the HOMOS of the donor and the LUMOs of the acceptor molecules are found by MNDO calculations. Nevertheless, with respect to the orbital symmetries, the same energy orders are obtained from both methods, although the absolute values of the orbital energies differ. Since HAM3 parameters have not yet been determined for elements beyond the second row of the periodic table we decided in favour of MNDO calculations. Furthermore, 2,3,7,8-tetrahydroxythianthrene was taken as a model compound of Vn,S,.This seemed tenable, because the expenditure of calcu- 171.6( 3) 169.7( 3) 124.6 (4) 120.3( 3) 114.0(4) 113.4(4) 143.0(5) 143.6(4) 136.3( 4) 133.9( 4) 138.6(4) 134.3(4) 146.3 (4) 148.2( 4) 144.4 (4) 149.7( 4) 178.4(4) 178.5( 3) 121.8 (2) 122.8( 2) 115.7( 2) 115.5(2) 122.6( 3) 123.3( 2) 122.6( 3) 119.8(2) 120.7( 3) 122.8(2) 116.8(3) 115.9(2) 122.6( 3) 121.7( 2) 114.9( 3) 117.0( 2) 122.6( 3) 121.3(2) lations for the tetramethoxy derivative would be out of all proportion to the attainable improvement in the results. The frontier orbitals in question, i.e. the HOMO of Vn,S2 and the LUMO of DDQ, are z-type orbitals and therefore very suitable for CT interactions between parallel planar molecules.These MOs are semi-occupied in the radical ions [Vn,S2]+ and [DDQI-. In each column only orbitals of the same type interact and an optimum overlap would be guaran- teed when the molecular planes are perpendicular to the stacking axes. However, probably to achieve closer packing, the molecular planes are inclined to the axes, but apparently in such a way that the MOs overlap quite well in these arrangements also (Fig. 4). Dielectric Relaxation of the CT Complex Experimental Dielectric relaxation measurements by the conventional ac technique were carried out with a Genrad 1689M bridge at 20 frequencies between lop2 and 102kHz in the tempera- ture range 167-360 K for Vn,S2 -DDQ and 220-420 K for Vn,Se, -DDQ, with steps of 5 "C.Each sample was moulded into a disc-shaped pill of diameter 1cm and thickness 1mm. Dielectric ac measurements of permittivity, E', and loss factor, E", clearly show two processes: at low temperatures a dielectric process and at high temperatures a conductive one. In Fig. 5, plots of E', E", us. T are shown for various frequencies in the range of the dielectric low-temperature process for both compounds. From an Arrhenius plot, lnf (at the maximum E") us. T-' (Fig. 6) we obtain values of 0.22 and 0.19 eV for the energies of activation, E,, of Vn2S2 -DDQ and Fig. 3 Segregated stacks of donors and acceptors in Vn,S, DDQ: (a) top view; (b) side view J. Muter. Chem., 1996, 6(4), 547-553 549 Fig. 4 (a) Relative positions of two successive donors and acceptors in the stacks of Vn,S,-DDQ, (b) overlap of the corresponding frontier orbitals Vn,Se, -DDQ, respectively In order to obtain more detailed information about this relaxation we have applied the Eynng equation /=-exp(g)kT 27th where k, h and R are the Boltzmann, Planck and gas constants, respectively, and AG is the Gibbs free energy of the barrier to the relaxation process, which is related to the activation enthalpy AH and activation entropy AS by AG=AH-TAS This leads to AS AHIn -f = In-k + ---T 2nh R RT where AH and the activation energy, E,, given by the Arrhenius equation are related by E, =AH +RT The values of AH and AS were determined directly from ln(f/T) us 1/T plots (Fig 6) and the results obtained are summarized in Table 5 Stark~eather~~held simple relaxations responsible for the processes of low activation entropy The dielectnc relaxation process is customarily represented in terms of E" us E' (Cole-Cole plots) Whereas for Debye-type peaks the curves are semicircles, the complex diagram plots representing the dielectic results associated with the dipolar relaxation are skewed arcs, which in many cases approach the real axis through a straight line, descnbed by the Havriliak- Negami (HN) equation 25 (3) where E~ and E, represent the relaxed and unrelaxed dielectric permittivity, respectively, of the relaxation process, zo is the relaxation time and a,y are parameters related to the shape and skewness of the complex dielectric plot (a is a parameter characterizing a symmetrical broadening of the distribution of relaxation times and y characterizes an asymmetrical one) A non-linear squares regression (NLSR)26 was used to improve the data fit The equivalent electric circuit (in series configuration involving a condenser, C, and an HN-type impedance, Z,, = [1+(~ozo)ol]y/zo[Co-C,]) shown in Fig 7 Table 5 Eynng equation parameters Compound AHfeV EaIeV ASlmeV K-' Vn, S2 DDQ 0 2037 0 2212 0 0028 Vn2Se, * DDQ 0 1772 0 1946 0 0027 550 J Muter Chem, 1996, 6(4), 547-553 150 200 250 300 I50 f ex %* xx X8 04 150 200 250 300 350 TI K X. :x0.xxe 0. % 4, 10 0 Fig. 5 Temperature dependence of the dielectnc permittivity E and loss E of (a) Vn,S2 * DDQ and (b) Vn,Se, DDQ at various frequencies (a,100Hzl x, 50Hz, U, 20Hz1 +, 10Hz, +, 5Hz) was employed in order to fit the experimental data, and the best set of parameters obtained for both compounds at different temperatures is given in Table6 The quality of the fit is demonstrated in Fig 8 The application of the HN equation to the dielectric loss data, ~"(o),provides an adequate functional form for the calculation of the dipolar correlation function, #(z) This is due to the fact that the dielectric permittivity is related to the dipole moment time correlation function, #(z), by a one-sided Founer or pure imaginary Laplace transformation 8-4-Cls a -4 --8 ! .I I 3 4 5 T-*/K-l Fig.6 Temperature dependence of fErr, (a) according to an Arrhenius equation (In f,~,, (b) according to an Eyring equation for [In us. TI); (f,,t/T)us. TI]for Vn,S,.DDQ (0,0)and Vn,Se,-DDQ (0,m) Fig. 7 Electrical circuit representing the dielectric process at low temperatures 0 20 40 60 80 6’ Fig. 8 Cole-Cole plot at 220 K for Vn, S2* DDQ (0,experimental data; a,calculated data) where o (=2nf)is the angular frequency and the total dipole moment time correlation function, #(z), is given by:27 where pk is the dipolar moment of each entity (dipole or dipole groups), assumed to be the same for all the entities. The time correlation function d(z) is obtained by a half- sided cosine Fourier transformation: E”O) cos wt dw where Ae =go -E, is the relaxation strength.The numerical evaluation of the preceding equation can be performed by depicting the dipolar process using the HN equation, for which: ~”(0)=AEr -sin yY r2= 1 +2(0z)” cos (a -3+ (OZ)~~ (7) (ozysin (a9) tan Y = I. 1 +(Ozy cos (a ;) where a, y, zo are parameters obtained with the fit of E* to the HN equation. In order to carry out the fit, we chose the Kohlrausch- Williams-Watts (KWW)28,29 function, given by: where zKWw,(a characteristic relaxation time) and ,8 (0 < P < l), (a parameter that describes the non-exponential character of the correlation function) are summarized in Table 6. Note that whereas the P parameters obtained from the KWW function remain practically constant over the entire temperature range, the distribution parameters, a and y, of the HN equation vary significantly with temperature.This is a consequence of the fact that different pairs of a and y values correspond to each /3 value because KWW is a single-parameter function whereas HN is a two-parameter one. The parameters of both functions are related by eqn. (9): by)’ =P (9) with c =0.95 and 1.28 for Vn2S2 DDQ and Vn2Se2 DDQ, respectively. Curves describing the evolution of this function with time at several temperatures are shown in Fig. 9. In the high-temperature process, E” continuously increases with decreasing frequency and no relaxation peak is seen. For this reason, the data were modelled using the electrical modulus Table 6 Havriliak-Negami equation parameters (A&,a, y, z~~)and Kohlrausch-Williams-Watts parameters (B,zKWw)for the CT complexes Vn, S2* DDQ 190 3.08 118.83 121.91 0.79 0.72 2.15 x 10-4 0.584 1.45 x 10-4 200 2.65 117.32 119.97 0.79 0.69 1.17 x 10-4 0.569 7.38 x 10-5 210 2.67 118.31 120.98 0.76 0.71 7.02 x lo-’ 0.557 4.78 x 10-5 220 2.79 121.48 124.27 0.78 0.70 4.75 x 10-5 0.561 3.08 x lo-’ Vn2Se2* DDQ 220 6.36 75.12 81.49 0.72 0.90 2.58 x lo-’ 0.570 2.72 x lo-’ 230 8.29 65.53 73.82 0.77 0.96 1.38 x lo-’ 0.669 1.47 x 10-5 240 9.88 62.48 72.36 0.79 0.87 6.42 x 0.655 5.89 x J.Muter. Chem., 1996, 6(4), 547-553 551 formalism according to M* =(&*)-l,where M'= &' (&')2 + (&")2 M" = E (&')2 + In the complex electric plot of M" us.M' a nearly exact semicircle was obtained as can be seen in Fig. 10. This proves I .00 T2 0.60 a 0.20 1 -15.00 -10.00 -5.00 0.00 5.00 w Fig. 9 Normalized correlation function calculated according to HN equation and KWW equation for Vn,S,.DDQ (0,0) and Vn,Se, * DDQ (0,U)(open symbols, experimental data; filled sym- bols, calculated data) 0.00) * 0 0-0.m mr 1 9 ?o o.oO0 ! 1I 1 I O.Oo0 0.002 0.004 0.006 QOOB M' Fig. 10 M' us. M" (Cole-Cole) plot at 360 K for Vn,S, -DDQ (0 experimental data, 0,calculated data) Fig. 11 Electrical circuit representing the conductive process at high temperatures that the process at high temperature is purely conductive. Accordingly, and following impedance spectroscopy tech-niques, we tried to fit the experimental data to the electrical model circuit given in Fig.11 and Table 7. Electrical Conductivity of the CT Complexes Experimental The electrical conductivity of Vn,S2 DDQ and Vn2Se2 DDQ were measured with an HP-4329-A electrometer together with a Guildline 6500 teraohmmeter by using silver-coated elec- trodes on samples moulded at ca. lo8Pa. The temperature range was 140-370K; each temperature at which measure- ments were taken was kept constant by use of a Pt-100 resistance thermometer and an Eurotherm 820 controller. Results The results of the conductivity measurements are given in Fig. 12. The absolute values of the conductivities are relatively low, but in both cases the temperature dependence of the conductivity can be described by eqn.(11): CJ =o0exp(-Ea/2kT) (11) b = -24 --201 Fig. 12 Arrhenius plot of In gac7In ad"vs. 1/T for Vn,S, -DDQ (0,0) and Vn,Se, -DDQ (El, U)(open symbols, experimental data; filled symbols, calculated data) Table 7 Parameters for the model of Fig. 11 giving the best fit with the experimental data for both CT complexes at different temperatures TIK Vn, S, -DDQ Vn, Se, * DDQ R cx 109 Ma R cx 1o'O MOJ 3 30 1.32 x 107 0.1287 0.00777 340 8.84 x lo6 0.1288 0.00776 1.98 x 107 0.9132 0.01095 350 8.55 x lo6 0.1314 0.0076 1 1.58 x 107 0.8974 0.01 114 360 6.43 x lo6 0.1327 0.00754 1.47 x 107 0.8870 0.01127 3 70 1.43 x 107 0.8708 0.01 148 552 J.Muter. Chew., 1996, 6(4), 547-553 Table 8 Conductivity data for some Vn,E, derivatives Vn,S, * DDQ Vn, Se, -DDQ 0.58 0.32 2.09 0.012 4.88 x 8.60 x Vn,S, * TCNQ" Vn,Se2 -TCNQ" 0.78 0.84 0.04 0.012 6.12 x lo-'' 8.20 x 10-9 2VnzSz * TCNEb 1.27 0.95 1.11 x lo-" 2Vn2 Se, -TCNE~ 1.17 0.96 8.32 x lo-'' Vn,Se, * Br; 1.07 0.0025 4.3 x 10-5 DNDTd 0.96 738 7.0 x lo-', "Ref. 3. bRef.2. 'Ref. 31. dDNDT=dinaphtho[2,3-b;2',3'-e][ 1,4]-dithiin-5,7,12,14-tetra0ne.~' where k = Boltzmann's constant, E, =gap energy, i.e. acti- vation energy of the electrical conductivity, and go= pre-exponential factor, i.e. conductivity at infinite temperature. This equation describes behaviour typical of semiconductors.The activation energies, E,, obtained from the slope of the Arrhenius plot (In CT us. 1/T) of the two conductivities (ac, dc) for both compounds are given in Table 8. We can see in Fig. 12 that the representation of dc conductivity displays two regions (at approximately 285 K the slope for both compounds changes significantly): a low-temperature region where the two activation energies are similar (Ea(ac)=0.50 eV, Ea(dC)= =0.58 eV for Vn2S2 -DDQ, Ea(ac)=0.31 eV, Ea(dC) 0.32 eV for Vn2Se2 DDQ) and a high-temperature region where E, rises to approximately 0.83 eV and 0.73 eV for Vn2S2 DDQ and Vn, Se, -DDQ, respectively. The first region may be explained in terms of an easy-path model and the second region is reached when the conduction through the grain boundaries (having a higher activation energy) exceeds the intragranular conduction.This result (two regions in Arrhenius plot) has also been observed by other authors for polycrystallinematerial^.^^*^^ The E, values (intrinsic conductivity) obtained for both compounds are of the same magnitude as the values of similar compounds such as Vn2S2 TCNE (0.78 eV) and 2Vn2S2-TCNE (0.95 eV). Owing to the fact that the charges of the donor and acceptor molecules are stoichiometric (+1 and -1, respectively), the conductivities of the compounds Vn2E2 DDQ (E = S, Se) are not very high, although they are significantly higher than in other compounds, such as Vn, E2 TCNQ and 2Vn, E2 -TCNE (Table 8).The central problem with ac measurements arises from the interpretation of the data. This is because the sample and electrode arrangement is electrically a 'black box', the equival- ent circuit of which (i.e.its representation by some combination of R and C elements) is often unknown. The crux of the problem in analysing ac data is (a) to determine the appropriate equivalent circuit for the cell and (b)to evaluate the various R and C components in the electric circuit. In polycrystalline materials the overall sample resistance may be a combination of the intragranular resistance (or bulk crystal resistance) and the intergranular (or grain boundary) resistance. Both resist- ances are parallel with an associated capacitance, and each parallel RC element gives rise to a semicircle in the complex plane z*.In the frequency range in which we worked, we observed only one semicircle associated with grain interior conductivity (intrinsic conductivity); for this reason, we employed the simple parallel RC element (Fig. 11). This work was supported by the Acci6n Integrada Hispano- Alemana (no. HA94-103, 322-ai-e-dv). We also thank the Volkswagenstiftung and the Fonds der Chemischen Industrie for financial support. M.D. gratefully acknowledges the grant by DAAD (NATO-fonds) M.J.S. acknowledges the Conselleria de Educacion y Ciencia de la Generalitat Valenciana for a grant. References 1 J. Behrens, W. Hinrichs, T. Link, C. Schiffling and G. Klar, Phosphorus Sulfur Silicon, 1995,101,235.2 P. Berges, J. Kudnig, G. Klar, E. Sanchez Martinez and R. Diaz Calleja, 2.Naturforsch., Teil B, 1989,44,211. 3 W. Hinrichs and G. Klar, J. Chem. Res., 1982, (S)336; (M)3540. 4 W. Hinrichs, P. Berges, G. Klar, E. Sanchez Martinez and W. GunDer, Synth. Met., 1987,20,357. 5 E. Sanchez Martinez, R. Diaz Calleja, W. GunDer, P. Berges and G. Klar, Synth. Met., 1989,30,67. 6 W. Gunoer, J. H. Henning, G. Klar and E. Sanchez Martinez, Ber. Bunsenges. Phys. Chem., 1989,93, 1370. 7 G. M. Sheldrick, SHELXTL-PLUS, Release 4.21/0, Siemens Analytical X-Ray Instruments, 1990. 8 W. Hinrichs, H-J. Riedel and G. Klar, J. Chem. Res., 1982, (S) 344; (M)3501. 9 H. Bock, A. Rauschenbach, C. Nather, Z. Havlas, A. Gavezzotti and G.Filippini, Angew. Chem., 1995,107, 120; Angew. Chem., Int. Ed. Engl., 1995,34,76. 10 W. Hinrichs, P. Berges and G. Klar, 2.Naturforsch., Teil By1987, 42, 169. 11 M. E. Peover, J. Chem. Soc., 1962,4540. 12 R. C. Wheland and J. L. Gillson, J. Am. Chem. SOC.,1976,98,3916. 13 G. Zanotti, A. Del Pra and R. Bozio, Acta Crystallogr., Sect. B, 1982,38,1225. 14 G. Zanotti, R. Bardi and A. Del Pra, Acta Crystallogr., Sect. B, 1980,36, 168. 15 Handbook of Chemistry and Physics, ed. R. C. Weast, CRC Press, Cleveland, OH, 1977-1978,58th edn., p. D-178. 16 E. Sanchez Martinez, R. Diaz Calleja, P. Berges, J. Kudnig and G. Klar, Synth. Met., 1989,32,79. 17 L. Asbrink, C. Fridh and E. Lindholm, Chem. Phys. Lett., 1977,52, 63; 69, 72. 18 L. Asbrink, C.Fridh and E. Lindholm, QCPE Bull., 1980,12,393. 19 M. J. S. Dewar and W. Thiel, J. Am. Chem. SOC., 1977, 99, 4899; 4907. 20 W. -Thiel, QCPE Bull., 1982, 2,438. 21 L. Asbrink, C. Fridh and E. Lindholm, Chem. Phys., 1978,27,169. 22 C. Fridh, L. Asbrink and E.oLindholm, Chem. Phys., 1978,27,159. 23 E. Lindholm, G. Bieri, L. Asbrink and C. Fridh, Int. J. Quantum Chem., 1978,14,737. 24 H. W. Starkweather, Jr., Macromolecules, 1981, 14, 1277; 1990, 23, 328. 25 S. Havriliak and S. Negami, Polymer, 1967,8, 161. 26 J. Ross McDonald, Complex Nonlinear Least Squares Immitance Fitting Program, LE VM6, 1993; Impedance Spectroscopy, Wiley-Interscience, New York, 1987. 27 G. Williams, Chem. SOC. Rev., 1978, 7, 89. 28 G. Williams and D. C. Watts, Trans. Faraday SOC.,1970,66,80. 29 R. Kohlrausch, Pogg. Ann. Phys. Chem., 1884,91,179. 30 A. R. West, Solid State Chemistry and its Applications, Wiley, Chichester, 1984, ch. 13. 31 E. Sanchez Martinez, R. Diaz Calleja and G. Klar, Synth. Met., 1990,38,93. 32 E. Sanchez Martinez, R. Diaz Calleja, J. Behrens, P. Berges, J. Kudnig, N. Wislki and G. Klar, J. Chem. Res., 1991, (S) 246, (M)2379. Paper 5/06484H; Received 2nd October, 1995 J. Muter. Chem., 1996, 6(4), 547-553 553

ISSN:0959-9428    

DOI:10.1039/JM9960600547

出版商:RSC    

年代:1996

数据来源: RSC

摘要:

Boron derivatives containing a bithiophene bridge as new materials for non-linear optics Catherine Branger," Minh Lequan,' Rose Marie Lequan,' Marguerite Barzoukasb and Alain Fortb "Laboratoire de Chimie et d'Electrochimie des matkriaux molkculaires, CNRS, URA 429 ESPCI 10 rue Vauquelin 75231 Paris Cedex 05, France bGroupe d 'Optique non linkaire et d'Opto-dectronique, IPCMS 23 rue du Loess 67037 Strasbourg Cedex, France New molecules with dimesitylboron as the acceptor group and bithiophene as the unsaturated chain have been synthesized and their non-linear optical properties investigated. The theoretical first hyperpolarizabilities determined by calculations are compared with experimental results. In the past few years interest has been focused on new organic materials with non-linear optical (NLO) properties.This effort was motivated by the good performances of organic molecules relative to the so far used inorganic crystals. The versatility of organic synthesis allows large modifications to the structure of molecules in order to create new ones in agreement with the required criteria. Molecules with good NLO activity are built according to the push-pull model, the delocalization of the electronic charge may be accomplished from the donor to the acceptor through a conjugated n-electron bridging moiety. Recently we have investigated the non-linear optical proper- ties of new molecules for which the unsaturated chain is biphenyl, (E)-stilbene or azobenzene, the donor being an N,N-dialkylamino group and the acceptor a dimesitylboron or a diphenylphosphine oxide.' Results showed that the boron group is an interesting acceptor in the internal transfer process, boron derivatives possessing high quadratic hyperpolarizability coefficients.In the search for molecules with good NLO properties we have synthesized new model molecules which combine the acceptor property of boron with bithiophene as the trans- mission chain. Thiophene has been described as a good elec- tronic transmitter because of its low stabilization energy (29 kcal mol-I) compared with benzene (36 kcal mol-')*t This reduced aromaticity makes the delocalization of electrons easier from the donor to the acceptor. For this reason, several reports have been published in which thiophene is used as the unsaturated chain in materials for NL0.3 The donor groups used in the present work are pyrrolidin-1-yl, dithian~lidene~ and 3-thienyl.The dipole moment of these molecules and their quadratic hyperpolarizability p were calculated by computer and the theoretical values were compared with experimental results. Synthesis The model compound 3 has been prepared from 2-pyrrolidin- 1-ylthiophene 1. The coupling reaction of 1 with 2-iodothio- phene, catalysed by a palladium(0) compound' gives the intermediate 2. The 5-(dimesitylboryl)-2,2'-bithiophene 4 prepared from bithiophene leads to the corresponding aldehyde 5 and the 3- thienyl substituted compound 7. The aldehyde 5 reacts with 1,3-dithiane to give 6.'r 1 cal=4.184 J. Experimental EFISH measurements First order hyperpolarizabilities were measured in dichloro- methane or in acetone using a standard setup equipped with a Q-switched Nd-YAG laser operating at 1064nm. The light source is shifted to 1907 nm by stimulated Raman scattering in compressed H, in order to minimize the dispersion factor by the resonance effect. Experiments were carried out in reduced intensity light. The dipole moments were measured by the use of a Gen- Rad capacitance bridge and calculated by the Guggenheim- Debye equation6 Synthesis Tetrahydrofuran (THF) and diethyl ether were freshly distilled over lithium aluminium hydride under argon bubbling before use. All the chemical experiments were carried out under an argon atmosphere.The structures of the products were checked by 'H NMR (300 MHz) spectroscopy and elemental analysis. 5-( Pyrrolidin-l-y1)-2,2'-bithiophene (2). The Pdo catalyst' was prepared from 2.0 g of dichlorobis( tripheny1phosphine)- palladium (2.85 x mol) and 5.8 cm3 of diisobutylalumin- ium hydride (1.0 mol dm-3 in hexane) in 65 cm3 of THF at 0 "C. To this solution were added 6.3 cm3 of 2-iodothiophene (57.0 x lop3mol) and a solution of 2-(pyrrolidin-l-yl)-5-thien-ylzinc chloride [prepared by treatment, at room temperature, 1 2 \ I 3 Scheme 1 Reagents: i, (a) BuLi, ZnCl,, (b) Pd', 24odothiophene; ii, BuLi, Mes,BF (Mes =2,4,6-trirnethylphenyl) J. Muter. Chem., 1996, 6(4),555-558 555 / 4 INt / 7 6 s vans SLJ It 6 S-CIS Scheme2 Reagents I, BuLi, Mes2BF, 11, BuLi, DMF, 111, (a) 1,3-dithiane, BuLi, Me,SiCl, (b)BuLi, 5, iv, BuLI, 3-bromothiophene, Pdo for 0 5 h, in 115 cm3 of THF, of the lithium salt of l7 (57 7 x mol) with 7 9 g of zinc chloride (57 9 x mol)] The reaction was stirred overnight, the THF removed and the mixture was hydrolysed and extracted with diethyl ether The black residue was separated by dissolving the product in hot hexane, filtering and then evaporation gave the crude product Crystallization from pentane afforded the title compound (6 4 g, 48%), mp 88 "C 5-(Dimesitylboryl)-5'-(pyrrolidin-l-yl)-2,2-bithiophene (3).A solution of the 5'-lithium salt of 2 [prepared from 3 65 g of 2 (15 5 x mol) in 140 cm3 of anhydrous THF at -25 "C for 1 h] was added to a solution of dimesityl(fluoro)boron in 50 cm3 of diethyl ether at -60 "C The reaction mixture was stirred overnight and then all the solvents were removed under reduced pressure, the residue was hydrolysed and the product extracted with diethyl ether The organic solution was dried and the solvent evaporated to yield a red oil Addition of pentane gave a red solid which was recrystallized from acetone to give pure title compound 3 (1 2 g, 16%), mp 182 "C 5-( Dimesitylboryl)-2,2'-bithiophene (4).The procedure was analogous to that descnbed for 3 using the corresponding lithium salt of bithiophene Purification was carried out by chromatography on silica using pentane as eluent The product was recrystallized from a mixture of acetone-pentane (1 1) to give the title compound as a yellow solid (64%), mp 131 "C 5-( Dimesitylboryl)-5'-formyl-2,2'-bithiophene (5).To a solu- tion of the 5'-lithium derivative of 4 [prepared from 5 7 g of 4 (13 75 x mol) in 80 cm3 of THF at -25 "C for 2 h] were 556 J Muter Chem, 1996, 6(4),555-558 added, at -60 "C, 6 0 cm3 of freshly distilled N,N-dimethylfor- mamide (DMF) The reaction mixture was kept under mag- netic stirring overnight and then the solvent was evaporated to dryness The residue was hydrolysed and the product extracted with diethyl ether The crude product was purified by chromatography over silica using pentane as eluent which is progressively enriched with dichloromethane After removal of the solvents, a purple residue was obtained This residue was dissolved in a minimum amount of dichloromethane and then hot methanol was added This solution was filtered and concentrated to give the title compound as a yellow solid (1 7 g, 28%) 5-( Dimesitylbory1)-5'-[( 1,3-dithian-2-ylidene)methy11-2,2'-bithiophene (6).To a solution of 2-lithio-1,3-dithiane (457 x mol) in 15 cm3 of THF, stirred at -25 "C for 1 h, was added, at -25 "C, 0 6 cm3 of chlorotrimethylsilane (4 7 x mol) under agitation for 0 5 h The temperature was allowed to reach room temperature (0 5 h) and then 45 cm3 of (1 6 mol dm3) butyllithium was added, at -25 "C, and the reaction mixture was stirred for 1 h at room tempera- ture s A solution of 5 (4 5 x lop3mol) in 15 cm3 of THF was introduced, at -25 "C, and the reaction was left overnight at room temperature After removal of solvents under reduced pressure, the residue was hydrolysed and the product extracted with diethyl ether The crude product was partially dissolved in cold methanol and filtered The solvent was evaporated and the product was purified by chromatography on silica using a mixture of pentane-dichloromethane (1 1) as eluent followed by recrystallization from pentane-dichloromethane (3 1) to give the title compound 6 (2 15 g, 88%), mp 17 4°C 5-(Dimesitylboryl)-2,2':5',3"-terthiophene (7).To a solution of 0 22 x loe3 mol of the Pdo catalyst prepared as described above were added 1 3 cm3 of 3-bromothiophene (13 9 x mol) and then, after cooling to -60 "C, the 5'-lithium derivative of 4(7 2 x mol) prepared as previously in 40 cm3 of THF was added and the reaction was stirred overnight After removal of THF, the mixture was hydrolysed and the product extracted with pentane Purification was carried out by chrom- atography on silica with pentane as eluent to give pure title compound 7 (0 4 g, 11 YO),mp 70 "C Results and discussion Experimental results Second order polarizabilites were measured by the EFISH technique (electrical field induced second harmonic generation) at 1907nm in order to minimize the dispersion factor by a resonance effect The experimental results are expressed as a scalar product ,upp(20) which is extrapolated to zero frequency by dividing it by the dispersion factor according to the two- state modelg to yield ,u/lP(0)where /lP(') is the projection of the vector p(0) along the direction of the dipole moment The quantity ,u/lp(')is an important factor in the non-linear proper- ties of polymers bearing such pendent molecules Table 1 summarizes the experimental results The quadratic hyperpolarizability of compound 7 was not measurable by this method, probably due to the low value of the product p/l which is a consequence of the small dipole moment (0 7 D) of the molecule A comparison of the charge transfer absorption bands of bithiophene derivatives with that of our reference 4-(di- mesitylboryl)-4'-(dimethylamino)biphenyl (BNB) shows an important red-shift which could suggest a large value for hyperpolarizabilities However, the experimental measure-ments do not confirm this prediction, the hyperpolarizabilities are not significantly different from that of BNB In contrast, the dipole moment of bithiophene derivatives 3 and 6 are twice Table 1 compound A,,,/nm" P/Db experimental(toluene) &EFISH(O)/lo-' esub Pi? esu BNB (ref.1) 3 376 470.5 2.0 4.0 85 (CH2C12) 148 (acetone) 42 37 6 7 435 400 3.6 0.7 112 (acetone) not measurable 31 - " Measured in the same solvent as for EFISH.The accuracy of experimental measurements is 10% for dipole moments and 20% for EFISH. 3 370 450 530 6 3 AInm Fig. 1 UV-VIS absorption of a solution of 3 in toluene exposed to daylight, (a) t =0 h, (b)t =2.5 h, (c) t =64 h as large as for the biphenyl analogue.This leads to higher values of the product ,u/?~('). Pyrrolidine is a good donor group, better than the dithianylidene in spite of the presence of the additional effect of the double bond. It is noteworthy that compound 3 possessing a pyrrolidine moiety, is photosensitive in solution as shown by the evolution of its UV-VIS spectrum in Fig. 1. A solution of 3 (2.8 x mol dm-3) in toluene exposed to the day light for 2.5 h in a quartz cell shows a decrease of absorbance of 1/3. After 2 days, the charge-transfer band (470.5 nm) disappears com-pletely to give rise to a band in the highest energy region (346 nm). For this reason, all measurements upon 3 were carried out in the absence of light.Calculations In order to explain the experimental results, theoretical investi- gations have been undertaken. Dipole moments and first hyperpolarizabilities were calculated for synthesized molecules and also for their biphenyl analogues. All the molecules investigated were pre-optimized by the use of the extensible systematic forcefield (esff) of the Discover 3 program incorporated in the BIOSYM" package. Semi-empiri- cal calculations have been performed by the AM1 method in the MOPAC program (version 6.0). This program defines the vector components of /?as shown in eqn. (1). PiAMl = 1/5 1(pijj+pjij +pjji> (1) j Taking account of the invariance of the hyperpolarizability coefficient towards the permutation of the last two indices and the Kleinman symmetry (absence of frequency dependence) the above formula is reduced to eqn.(2). The values of p determined by the EFISH technique were obtained by the use of eqn. (3), BiEFlSH =Biii + 1/3 C (Bijj+Vjji) (3) j#i which according to the above definition can be simplified to eqn. (4). BiEFISH(O) =Bixx(O) +PiyV(O) +Bizz(O) Therefore for comparison with experimental results, the theor- etical values pp(o)AM1 must be multiplied by 5/3. The results of the calculations are gathered in Table 2. A significant gain in ppC0)is observed when the biphenyl bridge is replaced by a bithiophene one. This improvement can be explained principally by two factors: (i) the low resonance energy of thiophene relative to benzene is favourable to an electronic transmission.(ii) The bithiophene transmitter is more planar than the biphenyl system, the torsion angle a between the thiophene units is less than 20" whereas this angle is found around 40" for the phenyl analogues, in the gas phase. Fig. 2 shows that the dithienyl rings adopt a transoid geometry which represents the most stable configuration. The compound s-cis-6 illustrates this planarity particularly well. This angle depends on the nature of the donor moiety as can be seen if one compares the torsion angles of 3, 6, and 7 (Table 2). As far as the dithianylidene donor group is concerned, two conformations are possible for compound 6 with regard to the double bonds. According to calculations, the s-trans conformer is the most stable one, in the gas phase, with a heat of formation of 84.4 kcal mol-', whereas this energy is of 91.0 kcal mol-', for the s-cis conformer.By contrast the dipole moments do not vary significantly between these two struc- tures. The experimental value of pp(0)determined for 6 is intermediate between those calculated for the two conformers (31 x lop3' esu) which suggests the coexistence of these two conformations in solution. The difference in enthalpy is negligible, less than 0.05 kcal, for the analogue 7. On the other hand, calculations confirm the small dipole moment of 7 (less than 1 D), which does not allow an effective orientation under an external electric field. Comparison of the N,N-dimethylamine in BNB and the pyrrolidine in 3' shows that the pyrrolidinyl group leads to higher values of the dipole moment and of the first order hyperpolarizability.The dithianylidene group is almost equiv- alent to the pyrrolidinyl one when biphenyl is the electron transmitter and it is slightly more efficient in the bithiophene series. This is confirmed by the results of the EFISH measure-ments which, taking account of the experimental error, are similar for these two substituents. Table 2 P:o'b PB,(O)compoundu p/D esu esu %/degrees' BNB 1.7 17.5 29.8 39.5 3 2.4 25.9 62.2 39.2 6' 2.3 22.4 51.5 38.6 7' 0.9 13.8 12.4 40.3 3 2.5 35.5 88.8 18.2 5-cis-6 2.7 44.8 121 0.9 5-trans-6 2.6 10.7 27.8 15.0 7 0.95 24.4 23.2 12.7 a 3,6 and 7' are 4-(dimesitylboryl)-4-( pyrrolidin-1-y1)-, 4-(dimes- itylboryl)-4'-dithianylidene-and 4-(dimesitylboryl)-4'-( 3-thieny1)- biphenyl, respectively.jYP(O) = 5/38,"' AMI. a= Angle between rings of the unsaturated chain. J. Muter. Chem., 1996, 6(4), 555-558 557 I Fig. 2 Molecules drawn and optimized by computer, (a) 5-(dimes-itylbory1)-5‘-(pyrrolidin-l-y1)-2,2’-bith10phene(3), (b) 5-(dimesityl-bory1)-5’-[( l73-dith1an-2-yhdene)methyl]-2,2 -bithiophene (6 s-cis) Conclusions We have synthesized new organic derivatives for non-linear optics beanng a Lewis acid as acceptor group, the dimesityl- boron entity, bithiophene as the unsaturated chain and pyrroli- dine- 1-yl, dithianylidene and 3-thienyl as donor moieties The results show that the replacement of the biphenyl unsaturated chain by bithiophene improves the dipole moment and the quadratic hyperpolarizabilities of the boron derivatives However, the geometry of the molecules is not always planar, it depends on the nature of the donor substituent The use of dithianylidene gives a more transparent material (by ca 35 nm) than the pyrrolidine analogue The pyrrolidine substituent is a better donor group than the dithianylidene one but the material is light sensitive This study confirms the good acceptor character of the boron atom in boron derivatives as has already been shown for 4-(dimesitylboryl)-4’-(dimethyl-amino) biphenyl (BNB) and 4-(dimesitylboryl)-4’(dimethyl-amino)azobenzene (BNA) Such derivatives may be attractive in the search for new NLO organic materials References 1 (a) M Lequan, R M Lequan and K Chane-Ching, J Muter Chem, 1991, 1, 997, (b) M Lequan, R M Lequan, K Chane-Ching, A C Callier, M Barzoukas and A Fort, Adu Muter Opt Electron, 1992, 1, 243, (c) K Chane-Ching, M Lequan, R M Lequan, C Runser, M Barzoukas and A Fort, J Muter Chem ,1995,5,469, (d)K Chane-Ching, M Lequan, R M Lequan and F Kajzar, Chem Phys Lett, 1995,242,598 2 (a)F Wheland, Resonance in Organtc Chemistry, Wiley, New York, 1955, p 99, (b)J March, Advanced Organic Chemistry, Wiley, New York, 3rd edn , 1985,37 3 (a) F Wurthner, F Effenberger, R Wortmann and P Kramer, Chem Phys , 1993, 173, 305, (b) F Effenberger, F Wurthner and F Steybe, J Org Chem, 1995,60,2082,(c)V P Rao, A K Y Jen, K Y Wong and K J Drost, Tetrahedron Lett, 1993, 34, 1747, (d)K Y Wong, A K Y Jen,V P Rao andK J Drost, J Chem Phys , 1994,100,6818,(e) V P Rao, A K Y Jen, K Y Wong and K J Drost, J Chem Soc Chem Commun, 1993, 1118, (f)M G Hutchings, I Ferguson, D J McGeein, J 0 Morley, J Zyss and I Ledoux, J Chem Soc Perkin Trans 2, 1995, 171, (8)G Mignani, F Leising, R Meyrueix and H Samson, Tetrahedron Lett, 1990,31,4743 4 V P Rao, Y M Cai and A K Y Jen, J Chem SOC, Chem Commun , 1994,1689 5 A 0 King, E Negishi, F J Villani and A Silveira, J Org Chem, 1978,43,358 6 E A Guggenheim, Trans Faraday SOC ,1949,45,714 7 S Scheithauer, H Hartmann and R Mayer, Z Chem ,1968,8,181 8 P F Jones, M F Lappert and A C Szary, J Chem SOC Perkin Trans, 1973,2272 9 (a) N Bloembergen and Y R Shen, Phys Rev, 1964, 133, 37, (b)J L Oudar and D S Chemla, J Phys Chem, 1977,66,2664 10 Biosym Technologies, Inc ,San Diego, CA, 92121-2777, USA Paper 5/06258F, Received 22nd September 1995 558 J Muter Chem, 1996, 6(4), 555-558

ISSN:0959-9428    

DOI:10.1039/JM9960600555

出版商:RSC    

年代:1996

数据来源: RSC