ISSN:0959-9428    

DOI:10.1039/JM99404FX029

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Edited by P.K. Datta, University of Northumbria at Newcastle J.S. Gray, University of Northumbria at Newcastle This title is published in three highly illustrated volumes and covers the latest developments in the subject. It provides a unique combination of the science of coatings and surfaces, the technologies of deposition, surface modification and analysis, and practical applications. The three volumes provide a useful and comprehensive blend of reviews and state-of-the-art papers, written by international experts, and reflect the current status of and likely future advances in surface engineering. Surface Engineering Fundamentals of Coatings Volume I: This volume considers principles of coatingsubstrate design in aqueous and high temperature corrosion, and wear properties, scanning the coatings spectrum from organic, through metallic to ceramic.The emphasis in this volume is on the sciencand design of coatings and substrate systems rather than on technology. Hardcover ISBN 0 85186 665 4 (1993) xvi + 370 pages Price f52.50 Volume 11:Surface Engineering Engineering Applications Volume II is dedicated to topics concerning the performance of coatings and surface treatments embracing four main areas: the inhibition of wear and fatigue; corrosion control; application of coatings in heat engines and machining; and qualities and properties of coatings. Hardcover ISBN 0 85186 675 1 (1993) xvi + 342 pages Price f52.50 Surface Engineering Process Technology and Surface Analysis Volume 111: Volume Ill has two thrusts as indicated by its title: process technology and surface analysis.Both areas are central to surface engineering and each holds particular promise, not only for improvement in existing types of coatings performance, but also in the design, development and evaluation of totally new coatinghubstrate systems. Hardcover ISBN 0 851 86 685 9 (1 993) xvi + 312 pages Price f52.50 Special Package Price (Volumes 1-111) f140.00 -save over lo%! Make sure you order without delay. .. To order, please contact: Turpin Distribution Services Ltd., Blackhorse Road, Letchworth, Herts SG6 1HN, United Kingdom Tel: +44 (0)462 672555 Fax: +44 (0)462 480947 ROYAL RSC members should obtain members’ prices and order from: @-SOCIETY OF Membership Administration CH EM1STRY Royal Society of Chemistry Thomas Graham House, Science Park, Milton Road, Cambridge CB4 4WF, Information United Kingdom Services Tel: +44 (0) 223 420066 Fax: +44 (0)223 423623

ISSN:0959-9428    

DOI:10.1039/JM99404BX031

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

ISSN 0959-9428 JMACEP(8) 1159-1358 (1994) Journal of Materials Chemistry Synthesis, structures, properties and applications of materials, particularly those associated with advanced technology CONTENTS 11 59 A convergent synthesis of extended aryl ester dendrimers W. J. Feast and N. M. Stainton 1167 Curing reactions in acetylene-terminated resins. Part 5.-Cyclotrimerization versus linear polyene formation in the catalysed cure of ethynylaryl-terminated monomers W. E. Douglas and A. S. Overend 1173 Examination of the structural features necessary for mesophase formation with aroylhydrazinato-nickel@) and -copper(n) complexes M. N. Abser, M. Bellwood, C. M. Buckley, M. C. Holmes and R. W. McCabe 1181 Gelation of silicone fluids using cholesteryl esters as gelators V.J. Bujanowski, D. E. Katsoulis and M. J. Ziemelis 1189 Interfacial chemistry and mechanical effects of a multifunctional processing additive on carbon black filled rubber R. H. Bradley, E.Sheng, I. Sutherland, P. K. Freakley and H. Ismail 1195 Aggregation control by vapour phase and heat treatments in Langmuir-Blodgett films of amphiphilic heteroarylazo dyes N. Kuramoto and M. Dan 1201 Electrochromic behaviour and X-ray structure analysis of a Pechmann dye, (E)-5,5’-diphenyl-3,3’-bifuranylidene-2,2’-dioneJ. Silver, M. T. Ahmet, K. Bowden, J. R. Miller, S. Rahmat, C. A. Reynolds, A. Bashall, M. McPartlin and J. Trotter 1205 Monolayer behaviour and Langmuir-Blodgett film properties of some amphiphilic phthalocyanines: Factors influencing molecular organisation within the film assembly M.J. Cook, J. McMurdo, D. A. Miles, R. H. Poynter, J. M. Simmons, S. D. Haslam, R. M. Richardson and K. Welford 1215 Cyclic voltammetry of zeolite-supported manganese porphyrins L. Gaillon, F. Bedioui and J. Devynck 1219 Magnetic properties and crystal structure of the p-fluorophenyl nitronyl nitroxide radical crystal: Ferromagnetic intermolecular interactions leading to a three-dimensional network of ground triplet dimeric molecules Y.Hosokoshi, M. Tamura, M. Kinoshita, H. Sawa, R.Kato, Y. Fujiwara and Y. Ueda 1227 Synthesis and optical spectroscopy of linear long-chain di-terminal alkynes and their Pt-o-acetylide polymeric complexes M. S. Khan, A. K. Kakkar, N. J. Long, J. Lewis, P. R. Raithby, P.Nguyen, T. B. Marder, F. Wittmann and R. H. Friend 1233 Soluble nickel bis(dithio1ene) oligomers for third-order non-linear optical studies C. A. S. Hill, A. Charlton, A. E. Underhill, S. N. Oliver, S. Kershaw, R. J. Manning and B. J. Ainslie 1239 In situ study of a strontium P-diketonate precursor for thin-film growth by atomic layer epitaxy J. Aarik, A. Aidla. A. Jaek, M. Leskela and L. Niinisto 1245 Investigations into the growth of A1N by MOCVD using trimethylsilylazide as nitrogen source J. Auld, D. J. Houlton, A. C. Jones, S. A. Rushworth and G. W. Critchlow 1249 Growth of ZnO by MOCVD using alkylzinc alkoxides as single-source precursors J. Auld, D. J. Houlton, A. C. Jones, S. A. Rushworth, M. A. Malik, P. O’Brien and G. W. Critchlow 1255 Characterization of Ru0,-based film electrodes by secondary ion mass spectrometry S.Daolio, B. Facchin, C. Pagura, A. De Battisti, A. Barbieri and J. Kristb 1259 Improvement of copper oxide-tin oxide sensor for dilute hydrogen sulfide T. Maekawa, J. Tamaki, N. Miura and N. Yamazoe 1263 Porosity of pyrolysed sol-gel waveguides J. J. Ramsden 1267 Sol-gel synthesis of superconducting YBa,Cu,O, using acetate and tartrate precursors A. Kareiva, M. Karppinen and L. Niinisto 1271 Preparation of single-phase Pb( Mg,,,Nb,,,)O, samples utilizing information from solubility relationships in the Pb-Mg- Nb-citric acid-H,O system J-H. Choy, Y-S. Han, S-W. Song and SH. Chang 1275 Synthesis and characterization of Ni,Sb,(OEt),, and its hydrolysis products G.Westin and M. Nygren 1283 Hydrothermal modification of electrocatalytic and corrosion properties in nanosize particles of ruthenium dioxide hydrate H. N. McMurray 1289 Determination of the potential limits for W03 colouration P. Shen and A. C. C. Tseung 1293 Phases in the Zr,Ta, -x(O,N)y system, formed by ammonolysis of Zr-Ta gels: Preparation of a baddeleyite-type solid solution phase Zr,Ta, -,O1 +,N, -,, 0 <x <1 J. Grins, P-0. Ka11 and G. Svensson 1303 Li,Ni,Ta06: A novel rock salt superstructure phase with partial cation order J. G. Fletcher, G. C. Mather, A. R. West, M. Castellanos and M. P. Gutierrez 1307 Synthesis and properties of a new p polymorph of Li,CrO, M. A. K. L. Dissanayake, S. Garcia-Martin, R. Saez-Puche, H. H. Sumathipala and A.R. West 1309 Inelastic neutron scattering study of hydrogen embrittlement in titanium alloys P. J. Branton, G. Burnell, P. G. Hall and J. Tomkinson 1313 Examination of the orientation dependence of the quasielastic scattering of neutrons by pellicular zirconium phosphate film R. C. T. Slade, H. A. Pressman, A. Peraio and M. Casciola 1319 Novel structural arrangement for divalent metal phosphonates: Synthesis of tert-butylphosphonates and structure of Co[(CO,)CPO,]-H,O J. Le Bideau, A. Jouanneaux, C. Payen and B. Bujoli 1325 Intercalation of polymerized 3-methyl- and 3,4-dimethyl-pyrrole in the VOPO, interlayer space H. Nakajima and G-e. Matsubayashi 1331 Zirconia formation by reaction of zirconium sulfate in molten alkali-metal nitrates or nitrites H.A1 Raihani, B. Durand, F. Chassagneux,D. H. Kerridge and D. Inman 1337 Ion exchange of ruthenium cationic complexes by a-tin(rv) bismonohydrogenphosphate M. J. Hudson and A. D. Workman 1343 Novel preparation of highly dispersed tungsten oxide on silica S. Colque, E. Payen and P. Grange MATERIALS CHEMISTRY COMMUNICATIONS 1349 Red bismuth emission in alkaline-earth-metal sulfates M. A. Hamstra, H. F. Folkerts and G. Blasse 1351 First ferrocene-containing side-chain liquid-crystalline polymers R. Deschenaux, I. Kosztics, U. Scholten, D. Guillon and M. Ibn-Elhaj 1353 Superconductivity up to 95 K in mercury-substituted 1212 thallium cuprates (T1,Hg),Srz+,,Nd, -,Cu,O, +6 F. LetouzC, S. Peluau, C. Michel, A. Maignan, C.Martin, M. Hervieu and B. Raveau ~~ ~ ~ 1357 Book Reviews: J. R. G. Thorne; J. H. Braybrook; G. C. Fettis 1 Cumulative Author Index ... 111 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)71-437 8656, Fax: +44 (0)71-287 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. I I

ISSN:0959-9428    

DOI:10.1039/JM99404FP071

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

Cumulative Author Index Aarik J., 1239 Abrahams I., 185, 775 Abser M. N., 1173 Agullo J. M., 695 Ahmet M. T., 1201 Ahn S-K., 949 Aidla A., 1239 Ainslie B. J., 1233 Aka G.. 907 Akhtar M. J., 1081 Akhtar Z.-u.-N., 1081 Akimoto H., 61 Aksay I. A., 353 Alagna L., 943 Ali-Adib Z., 1 Aliev A. E., 35 Allan N. L., 817 A1 Raihani H., 1331 Alves 0.L., 389, 529 An Y., 985 Ando M., 631 Andreani F., 1035 Angeloni A. S., 429, 437 Angeloni L., 1047 Annila A,, 585 ap Kendrick D., 399 Ara K., 551 Arai H., 653 Arai K.. 275 Aranha N., 529 Armelao L., 407 Armes S. P., 935 Armigliato A., 361 Arnold Jr. F. E., 105 Aruga Katori H., 915 Asaka N., 291 Aspin I. P., 385 Attfield J. P., 475, 575 Auld J., 1245, 1249 Auroux A,, 125 Azuma K.. 139 Baba A,. 51 Babu G. P., 331 Babushkin O., 413 Botto L.I., 541 Bowden K., 1201 Bradley R. H., 487, 1157, Branitsky G. A., 373 Branton P. J., 1309 Braybrook J. H., 1157, 1357 Brewis D. M., 487, 683 Britt S., 161 Brock T., 229 Brodsky C. J., 651 Brown T., 771 Bruce D. W., 479, 1017 Bruce P. G., 167 Bryant G. C., 209 Buckley C. M., 1173 Buist G. J., 379, 385 Bujanowski V. J., 1181 Bujoli B., 1319 Bulmer G., 1149 Burnell G., 1309 Busca G., 965, 1123 Bush T. S., 831 Cairns J. A., 393 Campelo J. M., 311 Caneschi A., 319, 1047 Cao X., 417 Capelletti R., 713 Carlino S., 99 Carr S. W., 421 Carrazan S. R. G., 47 Carruthers B., 805 Carvalho A., 515 Casciola M., 1313 Cassagneau T., 189 Castellanos M., 1303 Castiglioni M., 1067 Castillo R., 903 Catlow C. R. A., Causa M., 825 Cellucci F., 579 Cervini R., 87 Cesar C. L., 529 1189 781, 831, 1081 Dan M., 1195 Daolio S., 1255 Darriet B., 463 David L., 1047 Davidson I.M. T., 13 Davies A., 113 Davies M. J., 813 Deazle A. S., 385 De Battisti A., 1255 Dekker J. P., 689 del Arc0 M., 47 del Carmen Prieto M., 1123 Della Casa C., 1035 Delmon B., 903 Dennison S., 41 Depaoli G., 407 Deschenaux R., 679, 1351 De Stefanis A., 959 Devynck J., 1215 Dhas N. A., 491 Diamond D., 145, 217 Dissanayake Douglas W. E., 1167 Drabik M., 265, 271 Drennan J., 245 Dunmur D. A., 747 Durand B., 1331 Eda K., 205, 775 Eguchi K., 653 Ekstrand A., 615 Eldred W. K., 305 Ellis A. M., 13 Elsegood M. R. J., 891 Endregard M., 943 Ericsson T., 1101 Errington R. J., 891 Etourneau J., 463 Fabretti A., 1047 Facchin B., 1255 Faguy P. W., 771 Fau-Canillac F., 695 Feast W. J., 1159 Feng S., 985 M.A. K. L., 1075, 1307 Goodby J. W., 71, 747 Gopalakrishnan J., 703 Gormezano A., 817 Goto T., 915 Gozzi D., 579 Grange P., 1343 Granozzi G., 407 Gravereau P., 463 Greaves C., 931 Gregory D. H., 921 Grins J., 445, 1293 Guillon D., 679, 1359 Guo Z.. 327 Gutierrez M. P., 1303 Hall P. G., 1309 Hamerton I., 379, 385 Hamstra M. A., 1349 Han Y-S., 1271 Hannington J., 869 Harris F. W., 105 Harris K. D. M., 35 Harris S. J., 145, 217 Harrison W. T. A., 1111 Haslam S. D., 209, 1205 Hastie G. P., 977 Hatayama F., 205, 775 Hayashi A., 915 Heath K. D., 825 Heath R. J., 487, 683 Hector A. L., 279 Heinrich B., 679 Hermansson L., 413 Hervieu M., 1353 Heughebaert J-C., 765 Heughebaert M.. 765 Hickey E., 463 Higuchi A., 171 Hill C. A. S., 1233 Hinds B. J., 1061 Hirose N., 9 Hitchman M.L., 81 Hix G. B., 189 Hobson R. J., 113 Hochi K., 599 Jones A. C., 1215, 1249 Jones D. J., 18'4 Jones J. R., 37'1, 385 Jones P. J. V., 805 Jouanneaux A,, 1319 Jung K., 161 Jung W-S., 949 Kadokawa J-i., 551 Kaharu T., 859 Kahn-Harari A., 907 Kakkar A. K., 1227 Kang J. S., 747 Karasu M., 551 Kareiva A., 1267 Karppinen M., 1267 Kassabov S., 153 Kato C., 519 Kato R., 915, 1119 Katsoulis D. E., 337, 1181 Kawamura I., 237 Kennedy B. J., '(7 Kerridge D. H., 1331 Kershaw S., 1233 Khan M. S., 12.17 Kim H-B., 883 King T., 1 Kinoshita M., 915, 1219 Kiyozumi Y., 585 Klein M. L., 79; Klissurski D., li3 Knight K. S., 8!!9 Knowles J. C., 185, 775 KO E. I., 651 Kobayashi T., 291 Koch B., 903 Kohmoto T., 205, 775 Komatsu T., 53.1, 537 Komppa V., 58.' Kossanyi J., 139 Kosztics I., 1351 Kouyate D., 139 Kristo J., 1255 KriStofik M., 27 i Kill P-O., 1293 Bach S., 133, 875 Bachir S., 139 Badwal S.P. S., 257 Chaair H., 765 Challier T., 367 Chang S-H., 1271 Fernandez J. M., 11 17 Ferraro F., 1047 Fettis G. C., 1157, 1357 Hodby J. W., 469 Hodge P., 1, 869 Holmes M. C., 1173 Kubono K., 291 Kubranova M., 165 Kunitomo M., 205, 775 Badyal J. P. S., 1055 Charlton A,, 1233 Fisher G. A,, 891 Holmes P. A., 365 Kunou I., 955 Bae M-K., 991 Baetzold R. C., 299 Baffier N., 133, 875 Bagshaw S. A., 557 Bafios L., 445 Baram P. S., 817 Barbieri A,. 1255 Barbosa L. C., 529 Chassagneux F., 1331 Cheetham A. K., 641, 707 Chehimi M. M., 305, 741 Chen C., 469 Chen Q., 327 Cheng S. Z. D., Chernyaev S. V., 1107 Chevalier B., 463 105, 719 Fitzmaurice J.C., 285 Fitzpatrick A. D., 1055 Fleming R. J., 87 Fletcher J. G., 1303 Flint S. D., 509 Folkerts H. F., 1349 Forsyth M., 1149 Foster D. F., 657 Holmgren A., 413 Hong L., 1041 Hopkins J., 1055 Hosokoshi Y., 1219 Houlton D. J., 1245, 1249 Hourd A. C., 393 Howlin B. J., 379, 385 Hu Y., 469 Kuramoto N., 1195 Kuroda K., 519 Kuwano J., 9, 9"3 Labajos F. M., 1 117 Lacey D., 1029 Lahti P. M., 161 Landee C., 161 Laus M., 429, 437 Barker C. P., 1055 Barriga C., 1117 Chiba K., 551 Chiellini E., 429, 437 Fragala I. L., 1061 Fraoua K., 305 Hudson M. J., 99, 113, 1337 Hudson S. A., 479 Lawrence L. W., 571 Lawrenson B., 3'43 Barton J. M., 379, 385 Choisnet J., 895 Freakley P. K., 1189 Hughes A. E., 257 Lea M. S., 1017 Bashall A., 1201 Choy J-H., 1271 Frederiksen P., 675 Huxham I.M., 253 Le Bideau J., 13! 9 Battaglin G., 407 Chu P., 719 Friend R. H., 1227 Ibanez A., 1101 Lee C. K., 525 Battle P. D., 421. 641, 707, Ciacchi F. T., 257 Frfalova M., 271 Ibn-Elhaj M., 1351 Lee G. R., 1093 Batyuk V. A., 761 Bautista F. M., 311 831 Clegg W., 891 Colbourn E. A., 805 Cole-Hamilton D. J., 657 Fujii T., 635 Fujimoto T., 61, 533, 537 Fujita T., 955 Ichimura K., 883 Ikemoto H., 537 Imanishi N., 19 Lee S., 991 Lee S-I., 991 Leece C. F., 393 Bazin D.. 1101 Coles G. S. V., 23 Fujiwara Y., 1219 Imayoshi K., 19 Lefebvre F., 125 Bechgaard K., 675 Coles H., 869 Fukuda A,, 237, 997 Inada H., 171 Le Goff P., 133, 575 Bedioui F., 1215 Colque S., 1343 Gaillon L., 1215 Inman D., 1331 le Lirzin A., 319, 1047 Bedson J., 571 Beguin F., 669 Bell R.G., 781 Connell J. E., 399 Conroy M., 1 Conway L. J., 337 Gale J. D., 781, 831 Galikova t., 265, 271 Gallardo Amores Irvine J. T. S., 995 Ishikawa K., 997 Islam M. S., 299 Leskela M., 1234 Letouze F., 1353 Le van Mao R., fi05, 1143 Bellwood M., 1173 Cook M. J., 209, 1205 J. M., 965, 1123 Ismail H., 1189 Lewis A. L., 729 Benzi P., 1067 Cook S. L., 81 Galli G., 429, 437 Isoda S., 291 Lewis J., 1227 Bertoncello R., 407 Cooney R. P., 557 Ganguli P., 331 Isozaki T., 237, 997 Li J., 413 Beveridge M., 119 Copplestone F. A., 421 Garcia A., 311 Ivanovskaya M. I., 373 Li R, 773 Bigi S., 361 Corriu R. J. P., 987 Garcia-Martin S., 1307 Iyer R. M., 1077 Li X., 657 Bignozzi M.C., 429 Costa Bizzarri P., 1035 Garcia-Martinez O., 611 Jaek A., 1239 Lightfoot P., 167 Bjsrnholm T., 675 Costa F. M. A., 515 Gatteschi D., 319, 1047 James M., 575 Linda11 C. M., 617 Blasse G., 1349 Cox P. A., 805 Gee M. B., 337 Janes R., 1071 Lindback T., 413 Bonanos N., 899 Craig S. R., 977 Gibson R. A. G., 393 Jennings R. A., 931 Lindgren M., 223 Bonardi A.. 713 Crayston J. A., 1093 Gier T. E., 1111 Jimenez R., 5 Lindqvist O., llCl Bond S. E., 23 Crespin M., 895 Gil-Llambias F-J., 47 Jimenez-Lopez A., 179 Little F. J., 167 Booth C., 591 Critchlow G. W., 1245, Glomm B., 55 Jin-Hua C., 1041 Liu C-W., 393 Booth C. J.. 747 1249 Godinho M. M., 515 Joachimi D., 1021 Liu S.. 379 1 Liu-Cai F.X., 125 Lo Jacono M., 197 Long N. J., 1227 Lopez M. L., 547 Lorenzelli V., 965 Loubser G., 71 Lowe J. A., 771 Morpurgo S., 197 Mouron P., 895 Mozhaev A. P., 1107 Mueller J., 623 Muller W. F., 895 Mun M-O., 991 Munn R. W., 849 Povey I. M., 13 Poynter R. H., 1205 Predieri G., 361 Pressman H. A,, 501, 1313 Prosperi T., 943 Qi F., 1041 Qiu S., 735 Shirota Y., 171, 599 Shoji H., 1131 Shukla A. K., 703 Silver J., 1201 Simmons J. M., 1205 Simon M., 305 Sinclair D. C., 445 Tondello E., 407 Torres-Martinez L. M., Toyne K. J., 747 Trigg M. B., 245 Trotter J., 1201 Tschierske C.. 1021 Tseung A. C. C., 1289 5 Lucas V., 907 Luna D., 311 Lund A,, 223 Ma W., 771 MacFarlane D. R., 1149 Macklin W. J., 113 Mackrodt W. C., 817, 825 Madsen H. G., 675 Maeda K., 585, 1131 Maeda S., 935 Maekawa T., 1259 Mahgoub A.S., 223 Mai S-M., 591 Maignan A., 1353 Maireles-Torres P., 179, 189 Malandrino G., 1061 Malet P., 47 Murray K. S., 87 Nagae S-i., 591 Nakajima H., 1325 Nakajima T., 853 Nakano H., 171 Nakayama C., 631 Nakayama S., 663 Nameta H., 853 Narciso F. J., 1137 Neal G. S., 245 Neat R. J., 113 Netoff T. M., 1111 Neumayer D. A., 1061 Newton J., 869 Nguyen P., 1227 Nicol I., 29 Nielsen K., 867 Rahmat S., 1201 Raithby P. R., 1227 Ramsaran A,, 605, 1143 Ramsden J. J., 1263 Ranl~rv J., 867 Ratcliffe P. J., 1055 Raveau B., 1353 Raynor J. B., 13 Reid M., 1149 Rettig W., 1021 Reynolds C. A., 1201 Rhomari M., 189 Richards B. C., 81 Richardson R. M., 209, Rives V., 47, 1117 Roberts K. J., 977 1205 Singh N., 509 Slade R. C. T., 265, 367, 501, 509, 1313 Smart S.P., 35 Smith E. G., 331 Smith J. M., 337 Smith M. E., 245 Snetivy D., 55 Solano Reynoso V. C., 529 Solzi M, 361 Song S-W., 1271 Sotani N., 205, 775 Spagna A., 437 Sprik M., 793 Stainton N. M., 1159 Stedman N. J., 641, 707 Stern C. L., 1061 Tsuchida T., 631 Ueda M., 8x3 Ueda Y., 915, 1219 Ulibarri M.-A,, 1117 Underhill A. E., 1233 Ungar G., 719 Urbana M. R., 311 Uzunova E.. 153 Vaillant M., 765 van Aken P. A,, 895 van der Put P. J. , Van Grieken R., 499 Vancso G. J.. 55 Veiga M. L.. 547 Veringa H. J , 689 Viana B., 907 Vidgeon E. A,, 399 689 Malik M. A., 1249 Malins C., 1029 Mani R. S., 623 Manning R. J., 1233 Marcos M. D., 475 Marder T. B., 1227 Marinas J. M., 311 Marks G., 399 Marks T. J., 1061 Niinisto L., 1239, 1267 Nishiyama I., 449, 983 Niwa S-i., 585, 1131 Nomura R., 51 Nomura S., 171 Norman N.C., 891 Nunes M. R., 515 Nygren M., 615, 1275 O'Brien P., 565, 1249 Robertson A. D., 457 Robertson M. I., 29, 119 Rockliffe J. W., 331 Rodriguez-Castellon E., 179 Rodriguez-Reinoso F., 1137 Rojas R. M., 611 Romanovskaya V. V., 373 Ronfard-Haret J-C., 139 Rose R. G., 995 Stucky G. D., 1111 Styring P., 71 Su Q., 417 Suckut C., 5 Sumathipala H. H., 1075, Sundholm F., 499 Sutherland I., 487, 683, 1307 1189 Vivien D., 907 Volpe P., 1067 Wakagi A,, 973 Wang H., 417 Wanklyn B. M., 469 Watanabe T., 537 Watson G. W., 813 Watts J. F., 305 Welford K., 1205 Marsden J. R., 1017 Martin C., 1353 Martin T. L., 623 Ogawa M., 519 Ogura D., 653 Ohlmann A,, 1021 Ross A., 119 Rothlisberger U., 793 Rourke J.P., 1017 Suto S., 631 Suzuki T., 631 Suzuki Y., 237 Weller M. 'I.921 Wen J., 327 Wen-Tao Y., 1041 Mather G. C., 1303 Ohnishi K., 171 Rowatt B., 253 Svensson G., 1293 Wessels P. I.., 71 Mathieson I, 1157 Matsuba T., 599 Matsubayashi G-e., Matsuda H., 51 Matsuda T., 955 1325 Ohta K., 61, 533, 537 Ohtaki M., 653 Oki K., 635 Oliver S. N., 1233 Olivera-Pastor P., 179 Rowley A. T., 285 Roziere J., 189 Ruiz P., 903 Rushworth S. A,, 1245, 1249 Swindell J., 229 Taga T., 291 Tagaya H., 551 Tajbakhsh A. R., 1017 Takahashi M., 519 West A. R., 5, 445, 457, 525, West D., 1 Westin G., 615, 1275 Williams G.. 23, 1157 647, 1075, 1303, 1307 Matsuzaki I., 853 Osterlund R., 615 Russell D. K., 13 Takahashi S., 859 Williamson C. J., 565 Maury F., 695 Maza-Rodriguez J., 179 McCabe R.W., 1173 McCarrick M., 217 McGhee L., 29, 119 Overend A. S., 1167 Owen J. R., 591 Pagura C., 1255 Painter J., 1153 Pan W-P., 771 Ryan T. G., 209 Sadaoka Y., 663 Saez-Puche R., 1307 Salatelli E., 1035 Sanchez Escribano V., 965, Takanishi Y., 997 Takano M., 19 Takebe Y., 599 Takeda Y., 19 Takeuchi M., 955 Winfield J. bf., 29, 119 Wittmann €, , 1227 Wolf M., 839 Wong Chi Man M., 987 Workman A D., 13, 1337 McKeown N. B., 1153 Pareti L., 361 1123 Takezoe H., 237, 997 Xiao F-S., 735 McMeekin S. G., 29, 119 Parker M. J., 1071 Sano S., 275 Tamaki J., 1259 Xiao S., 605, 1143 McMurdo J., 1205 Parker S. C., 813 SanoT., 1131 Tamura M., 915, 1219 Xu R., 735. 985 McMurray H. N., 1283 McPartlin M., 1201 Meakin P., 1149 Mellen R.S., 421 Parkin I. P., 279, 285 Parsonage J. R., 399 Partridge R. D., 1071 Patil K. C., 491 Santiago J., 679 Sastry P. V. P. S. S., 647, Saunders V. R., 825 1077 Tan M. P., 525 Tanabe K., 853 Tanaka T., 859 Tarasconi P., 713 xu w., 735 Xu Y., 985 Yakhmi J. V., 1077 Yamamoto tl., 635 Mendonqa M. H., 515 Merkelbach P., 615 Metcalfe K., 331 Michel C., 1353 Miles D. A,, 1205 Miller J. D., 729 Miller J. R., 1201 Mills G. P., 13 Minelli G., 541 Min-Hua J., 1041 Mirtcheva E., 611 Mishima S., 853 Miura N., 631, 1259 Miyamae N., 955 Mizukami F., 585, 1131 Mohanty D. K., 623 Monk P. M. S., 1071 Moreau J. J. E., 987 Moretti G., 541 Payen C., 1319 Payen E., 1343 Pelizzi C., 713 Peluau S., 1353 Pennington M., 13 Peraio A., 1313 Percec V., 719 Pereira-Ramos J-P., 133, Perez G., 959 PCrez-JimCnez C., 145 Petrov K., 611 Pettiti I., 541 Philippot E., 1101 Pic0 C., 547 Picone P.J., 571 Pigois-Landureau E., 741 Porta P., 197, 541 Pottgen R., 463 875 Sawa H., 915, 1219 Sawada M., 859 Saydam S., 13 Scholten U., 1351 Schoonman J., 689 Sergeev G. B., 761 Seron A., 669 Sessoli R., 1047 Shabatina T. I,, 761 Shamlian S. H., 81 SharmaV., 703 Shen D., 105 Shen P., 1289 Sheng E., 487, 683, 1189 Sheridan P., 161 Sherrington D. C., 229, 253 Sherwood J. N., 977 Shimokawatoko T., 51 Shiomi D., 915 Tetley L., 253 Thanapprapasr K., 591 Thanh Vu N., 1143 Thatcher J. H., 591 Thebault J., 669 Thepot P., 987 Thery J., 907 Thomas H. J., 541 Thomas J. O., 839 Thomas M. J. K., 399 Thomson J. B., 167 Thorne A. J., 209 Thorne J.R. G., Tian M., 327 Toba M., 585, 1131 Tomellini M., 579 Tomkinson J., 1309 Tomlinson A. A. G., 943, 1157, 1357 959 Yamamoto I., 61, 533, 537 Yamamoto (I., 19 Yamazoe N , 631, 1259 Yang H., 55 Yao J., 605 Yarovoy Y. K., 761 Yogo T., -353 Yokoyama .4., 983 Yoon Y., 719 Yoshizawa A,, 449, 983 Yu H., 327 Yue Y., 985 Zarbin A. J G., 389 Zhang W-r., 161 Zhao L., 623 Zheng Q., 1041 Zhuang Z.. 1041 Ziemelis M. J., 1181 Zotov N., 611 11 Conference Diary 1994 0 Denotes a new or amended entry this month August 11-16 Supramolecular Chemistry: 100 Years SchlosgSchlussel Prinzip Mainz, Germany Dr. Josip Hendekovic, European Science Foundation, 1 quai Lezay-MarnBsia, 67080 Strasbourg Cedex, France Tel: +33 88 76 71 35; Fax: +33 88 36 69 87 August 2 1-26 Molten Salts Bad Herrenalb, Germany Dr.Josip Hendekovic, European Science Foundation, 1 quai Lezay-Marnbsia, 67080 Strasbourg Cedex, France Tel: +33 88 76 71 35; Fax: +33 88 36 69 87 August 21-26 1994 ACS National Autumn Meeting Washington,DC, USA ACS International Activities Office, 1155 16th St. NW, Washington, DC 20036, USA August 28-ECM 16, European Crystallographic Meeting September 2 Dresden, Germany Professor P. 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ISSN:0959-9428    

DOI:10.1039/JM99404BP073

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994,4(8), 1159-1165 A Convergent Synthesis of Extended Aryl Ester Dendrimers W. James Feast and Neil M. Stainton IRC in Polymer Science and Technology, University of Durham, Durham, UK DH 1 3LE A convergent synthesis of aryl ester dendrimers with flexible spacer units via a series of ‘dendron wedges’ of increasing size is described. The development of a high yield iterative protection/deprotection scheme for phenolic groups as acetates, in the presence of aryl esters, enables dendrimers to be assembled using this approach. In recent years there has been significant interest in well- defined, highly branched polymeric species, and the unusual characteristics that arise in these materials as a consequence of their novel topologies and molecular structures.’ The synthesis of macromolecular, three-dimensional species with hyperbranched architecture was pioneered by Tomalia et aL2 and Newkome et d3in the early eighties.Since then, there have been many reports of the stepwise synthesis of families of monodisperse polymeric species. Such materials have been termed ‘starburst’ polymers or dendrimers (from the Greek, dendritic =treelike), on account of their highly branched topology. Two distinct techniques have emerged for the stepwise synthesis of dendritic polymers. The first of these, the so-called divergent route, starts at the centre of the molecule and proceeds outwards by means of an appropriate iterative scheme; however, with increasing dendrimer size, or gener- ation, the number of repeat units in the formation of each successive layer increases rapidly, following a geometric pro- gression and ultimately leads to practical difficulties involving isolation and purification of products due to the problems associated with incomplete reaction at increasingly congested reaction sites.More recently, convergent techniques have been developed, notably by Hawker and FrC~het,~ and used by a number of groups working in the field. In this approach, dendrimer construction commences at what will ultimately be the periph- ery of the molecule and progresses inwards uia a series of ‘dendron wedges’ of increasing size that can be attached to the core molecule in the final step. It is this technique that has been utilised by Miller et aL5 in their synthesis of a series of aryl ester dendrimers based on 5-hydroxyisophthalic acid.Unlike their linear analogue, poly( p-hydroxybenzoic acid), which is essentially infusible and insoluble and consequently extremely difficult to process, such dendrimers have been found to be highly soluble in a wide range of common organic solvents. Here we report the synthesis of polyester dendrimers uia a convergent route incorporating linear aromatic spacer or extension units between successive branch junctions in order to assess their thermal, chemical and mechanical properties with a view to exploring the potential of such materials for novel applications. In this way, we combine the concept of dendritic layer-block copolymers of Hawker and Frechet6 with aryl ester dendrimer synthesis similar to that of Miller et aL5 Our novel approach to dendrimer synthesis utilizes acetates as protecting groups in the preparation of polyaryl esters as opposed to the silyl ether protection used by Miller et al.’ Results and Discussion We have prepared a series of three aryl ester dendrimers, having 7, 16 and 19 aromatic rings via a convergent route involving the development of an iterative protection/deprotec- tion scheme for phenolic groups as acetates in the presence of aryl esters.The synthesis is based on the reaction of 5-acetoxyisophthaloy1 dichloride, 2 (the branching urtit) and 4-acetoxybenzoyl chloride, 1 (the spacer unit) with a series of phenolic ‘dendron wedges’ and subsequent selectik e ester cleavage to yield wedges of increasing size (see Scheme 1).The acid chlorides were prepared in a two-step process from the appropriate hydroxyacids, which are commercially avail- able. Initial acetylation of the phenol groups with acetic anhydride in basic aqueous solution was followed by conver- sion to the acid chloride by reaction with phosphorus penta- chloride. Overall yields of typically 86-89% were obtained. To overcome the increasingly cumbersome nomenclature for the larger aromatic molecules, these are named with reference to the number of aromatic rings in the structure followed by an abbreviation indicating the reactive functional group (see Scheme 1). Reaction of 4-acetoxybenzoyl chloride, 1, with phenol in a solution of dichloromethane and pyridine with 4-dimethylaminopyridine (DMAP) catalysis5 yielded phenyl 4-acetoxybenzoate, [21-OAc (see Scheme 1).The conversion of [21-OAc to phenyl 4-hydroxybenzoate, [2]-OH, was first attempted by selective reduction with sodium borohydride under mild condition^,^ a technique successfully employed by ourselves in related work involving alkyl benzoates.Despite prolonged reaction times, no change was detected and the phenyl acetate remained intact. On reaction of [2]-OAc with ethanolic potassium hydroxide on a small scale at 0 “C, yields of the desired product were obtained in excess of 70%; however, on scaling up this process, significant phenol con- tamination was observed, indicating the lack of specificity of the reaction.Following purification by vacuum sublimation, [2]-OH was obtained in low yield. Reaction of the trifunc- tional core molecule, benzene-l,3,5tricarbonyltrichloride, 3, with the deprotected product, [2]-OH, in dichloromethane- pyridine solution with DMAP catalysis yielded 171, the extended first-generation dendrimer, in high yield and without the need for purification by column chromatography. In a similar manner, [5]-OAc, the protected second-generation wedge was prepared by reaction of [2]-OH with 5-acetoxyisophthaloy1 dichloride, 2, in excellent yield. The deacetylation of [51-OAc was initially attempted using borohydride reductive hydrolysis. Analysis of the products revealed a significant proportion of [2]-OH, indicating aryl benzoate hydrolysis.Other basic hydrolysis techniques were equally unsuccessful and resulted in undesirable fragmen- tation. Investigation of acid-catalysed deacetylation showed that a 10% v/v aqueous hydrochloric acid solution and tetrahydrofuran mixture was suitably regiospecific and gave [5]-OH cleanly and in high yield. Adaptation of this pro- cedure for [2)-OH synthesis was only partially successful and an appreciable quantity of phenol was produced. The yield of J. MATER. CHEM., 1994, VOL. 4 Q0.pO 0..Q.o [71 [2]-OH did not justify changing from the preferred mode of synthesis as previously described. From the experience of other re~earchers,~ who concluded that the coupling of large branched aryl ester wedges to an aromatic core using either pyridine or DMAP resulted in significant ester exchange, the weaker base, N,N-dimethylani- line, was used to catalyse the reaction of [5]-OH with benzene-1,3,5-tricarbonyltrichloride 3 to produce [161, the second-generation dendrimer, after purification by column chromatography. The extended second-generation wedge, [6]-OH, was pre- pared by the reaction of 4-acetoxybenzoyl chloride 1 with [5]-OH in dichloromethane-pyridine solution with DMAP followed by acid-catalysed deacetylation.This wedge was attached to the core molecule 3 using the method described above, to yield [191, the extended second-generation dendrimer. We have tried unsuccessfully to prepare larger dendrimers using this route.The synthesis of [13]-OAc, the protected third-generation wedge, from [6]-OH with 5-acetoxy-isophthaloyl dichloride 2 has been carried out without prob- lem; however, attempts to deprotect this in aqueous acid-THF solution have failed. IR spectroscopy of the product indicated that appreciable aryl ester hydrolysis had taken place. It is significant to note that similar problems have been experienced in related systems for wedges of a comparable size.5 It is possible that the increasing extent of aryl ester hydrolysis with increasing size of wedge, as compared to removal of the protecting group, may be attributed at least in part to the folding back of the large dendrimer branches towards the focal point of the wedge, thus congesting the reactive site and compounding the already serious problem of undesirable aryl ester hydrolysis, resulting simply as a result of the increasing aryl ester: acetate ratio.Characterisation of the Dendrimers On account of the high symmetry of the dendrimers, both 'H and I3C NMR spectroscopy have proved invaluable in the characterisation of these materials. Two-dimensional hetero- nuclear correlation NMR spectroscopy has been utilised for the unambiguous assignment of individual proton and carbon resonances within the structures. The assignments follow in a straightforward way from the spectra of the wedge compo- nents in the synthetic route, bearing in mind relative peak intensities and correlation tables of chemical shifts of related compounds (see Fig.1 and 2). The dendrimers have also been characterised by elemental analysis and gel permeation chromatography (GPC) (see r191 Fig. 3). For [7] and [16], elemental analysis shows close agreement with the theoretical values whilst GPC illustrates their monodisperse nature. Elemental analysis and GPC of [19] indicate the presence of a small quantity of impurity that could not be removed by column chromatography. GPC is consistent with the hypothesis that this trace impurity is unreacted wedge material. Characterisation by mass spec-trometry has also been attempted using conventional CI and EI techniques; however, both of these have resulted in frag- mentation to species containing only single aromatic units and no molecular ions have been detected.The dendrimers are highly soluble in organic solvents such as chloroform, dichloromethane and THF, contrasting mark- edly with their linear analogue poly (p-hydroxybenzoic acid), which is virtually insoluble in common organic solvents. Thermogravimetric analysis has shown that at a constant heating rate of 10°C min-' in a nitrogen atmosphere, the dendrimers retain 98% of their mass up to around 400°C. Wide-angle X-ray powder diffraction indicates that [7] is crystalline whereas both [16] and [19] are less well ordered compounds (see Fig.4). Heat of fusion measurements by differential scanning calorimetry support this view (Table 1 ). Experimental All organic reagents were obtained from Aldrich and used without further purification.Melting points were obtained on an Electrothermal digital melting point apparatus unless otherwise stated and reported without correction. IR spectra were recorded on a Perkin-Elmer 1600 series FTIR. Thermogravimetric analyses were carried out using a Shimadzu TGA-50. Differential scanning calorimetry was performed on a Perkin-Elmer DSC-7 at a scanning rate of 10°C min-l. 'H and 13C NMR spectra were recorded on a Varian 200 MHz Gemini or Varian 400 MHz spectrometer, as indicated, and were referenced to TMS. Gel permeation chromatography was carried out in chlorFform ?sing thre? 5 pm columns of PL gel with pore size 100 A, lo3 A and lo5A and a Waters differential refractometer detector.X-Ray diffraction was carried out on a Siemens Diffraktometer D5000. 4Acetoxybenzoic Acid To a stirred solution of 4-hydroxybenzoic acid (225.00g, 1.63mol) in aqueous sodium hydroxide solution (2.7 1,2.5 mol 1-l) cooled in an ice-water bath, acetic anhydride (750 ml) was added slowly. Stirring was continued until the mixture solidified, upon which the flask was shaken for 10min and J. MATER. CHEM., 1994, VOL. 4 [2]-OAc [2]-0H o\ ?00 t I oQg-c, [6]-OAc 3, 8 H', THF pyridie, DMAP Cocl b KOH.E!OH pyridine, DMAP f 3, N,N -dimethylaniline d c'Tfrn'2, OCOCH3 pyridine,DMAP Scheme 1 Outline routes to dendrimers [7], [16] and [19] the contents acidified to pH 1 using concentrated hydro-chloric acid.The white slurry was filtered and the filtrate extracted with ethyl acetate (4 x 300 ml). A further portion of ethyl acetate (900 ml) was added to this and the filtered off residue was dissolved in it. The resulting solution was washed with water (5 x 1 1) and the combined aqueous washings extracted with ethyl acetate (500 ml). The organic portions were combined, dried (MgS04), the solvent removed by evaporation and the residue dried under vacuum at 80 "C for 4h. to yield a white powdery solid (272.04 g, 1.51 mol, 92.7%). Mp 188.0-189.5"C (lit. 191-192°C). 'H NMR (CDCl,, 200 MHz), 6 2.34 (s, 3H, CH,), 7.21 (d, 8.96 Hz, 2H, ArH), 8.15 (d, 8.90 Hz, 2H, ArH). I3C NMR (CDCI,, 200 MHz) 6 21.66 (CH,), 122.26 (aromatic C-H), 127.31 (aromatic C-R), 132.37 (aromatic C-H), 155.48 (aromatic C-0), 169.35 (ArCO,H), 171.83 (COCH3).v,,Jcm-': 2996.0, 1754.5, 1681.1. CAcetoxybenzoyl Chloride An intimate mixture of 4-acetoxybenzoic acid (304.88 g, 1.69 mol) and phosphorus pentachloride (358.01 g, 1.72 mol) in a flask fitted with a reflux condenser and gas absorption device was warmed gently with a heat gun to initiate the reaction and shaken occasionally until the vigorous evolution J. MATER. CHEM., 1994, VOL. 4 f a I I oi ari91 I b Fig. 1 13C NMR spectra of dendrimers in CDCl, of hydrogen chloride had ceased. The reaction mixture was stirred for a further 30min at room temperature to form a pale yellow homogeneous oil. After removal of phosphorus oxychloride by distillation at atmospheric pressure, the residue was distilled at reduced k 22.50 24.30 26.10 t /min Fig.3 GPC of dendrimers [71, [161 and [191 pressure (107 "C, 0.4 mbar) to produce a clear colourless oil that yielded a white crystalline solid (317.51 g, 1.60 mol, 94.5%) on cooling. Mp 29.5-30.5 "C(lit. 29-30 "C). 'H NMR [2H,]acetone, 200 MHz) 6 2.33 (s, 3H, CH,), 7.41 (d, 9.08 Hz, 2H, ArH), 8.20 (d, 9.00 Hz, 2H, ArH). 13C NMR ([2H,]acetone, 200 MHz) 6 21.42 (CH,), 124.05 (aromatic C-H), 131.35 (aromatic C-R), 134.26 (aromatic C-H), 158.11 (aromatic C-0), 168.00 (COCl), 169.42 (COCH,). v,,Jcm-': 1773.8, 1597.4, 1499.3, 1370.3, 1199.4, 1162.1. Phenyl 4-Acetoxybenzoate, [21-OAc To a suspension of 4-acetoxybenzoyl chloride (315.75 g, 1.59 mol) in pyridine (1350 ml) were added phenol (179.47 g, 1.91 mol), 4-dimethylaminopyridine (9.74 g, 0.080 mol) and dichloromethane (650 ml).After it had been stirred at room temperature for 48 h, the solution was washed with aqueous hydrochloric acid (15 x 400 ml, 10% v/v), aqueous sodium hydroxide (15 x 400 ml, 1.0 mol 1-I) and aqueous potassium carbonate (2 x 300 ml, 1.0 mol-l), dried (MgS04), the solvent removed by evaporation and the residue dried under vacuum to yield a light tan solid (376.79 g, 1.47 mol, 92.5%). Mp 83.5-85.5 "C. 'H NMR (CDC13, 200 MHz) 6 2.33 (s, 3H, CH3), 7.22 (m, 5H, ArH), 7.43 (m, 2H, ArH), 8.23 (d, 8.58Hz, 2H, f n 136 1 32 128 124 120 W2) Fig. 2 2D Heteronuclear correlation spectrum of [16] in CDC1, J.MATER. CHEM., 1994, VOL. 4 1 I I' 10 20 30 40 50 60 70 80 90 2Hdegrees Fig. 4 Wide-angle X-ray diffraction traces of [71, [161 and [191 ArH). I3C NMR (CDCl,, 200 MHz) 6 21.67 (CH,), 122.19, 122.38, 126.47 (all aromatic C-H), 127.59 (aromatic C-R), 130.03, 132.30 (both aromatic C-H), 151.36, 155.32 (both aromatic C-0), 164.89 (ArC=O), 169.32 (CH,C=O). vmax/cm-l: 3068.0, 1755.2, 1728.9, 1601.5, 1501.9, 1485.2. Phenyl4Hydroxybenzoate, [2]-OH To an ice-cold solution of sodium hydroxide (31.16 g, 0.779 mol) in ethanol (1.3 1) was added phenyl 4-acetoxy- benzoate (199.44 g, 0.779 mol) and the mixture stirred at 0 "C for 30 min. The mixture was filtered and water (6 1) was added to the filtrate and the solution acidified to pH 1 with concen- trated hydrochloric acid.The resultant precipitate was col- lected by filtration, washed with aqueous hydrochloric acid (10% v,/v) then hexane and dried under vacuum at room temperature overnight. The filtrate was extracted with ethyl acetate, the organic layers combined, dried (MgS04) and the solvent removed by evaporation to yield a white residue that was dried under vacuum. The crude product portions were combined and purified by vacuum sublimation (ca. 210 "C, 0.3 mbar) followed by recrys- tallisation from hot toluene and washed with cold toluene and hexane to yield a white crystalline solid (72.57g, 0.339 mol, 43.5%) Mp 184.0-185.0 "C (lit. 170-174 "C). 'H NMR C2H,]acetone, 400 MHz) 6 7.01 (d, 9.2 Hz, 2H, ArH), 7.26 (m, 3H, ArH), 7.45 (m, 2H, ArH), 8.06 (d, 8.8 Hz, 2H, ArH), 9.36 (s, lH, OH).13C NMR ([2H6];icetone, 400 MHz) 6 115.56 (aromatic C-H), 120.88 (aromatic C-R), 122.06, 125.63, 129.42, 132.36 (all aromatic C-H). 151.52 (aromatic C-0), 162.50 (aromatic C-OH), 164.45 (C=O). v,,Jcm-': 3397.6, 3055.9, 1698.8, 1603.4, 1585.3, 1509.6,851.8. Extended First-generation Dendrimer, [71 To a solution of benzene-1,3,5-tricarbonyltrichloride (5.31 g, 0.0200 mol) in pyridine (220 ml) were added phenyl 4-hydroxybenzoate ( 15.00 g, 0.070 1 mol), 4-dimethj lamino- pyridine (0.40 g, 0.033 mol) and dichloromethane (80 ml) and the solution stirred at room temperature for 4 days. After addition of a further portion of dichloromethane (250 ml), the solution was washed with aqueous hydrochloric acid (4 x 250 ml, 10% v/v), aqueous sodium hydroxide (3 x 250 ml, 1.0 mol 1-I) and brine (2 x 250 ml I, dried (MgS04) and the solvent removed by evaporation.The residue was recrystallised from a mixture of ethyl acetate and ethanol (3: 1). On drying under vacuum at 100 "C overnight, this yielded a white powdery solid (12.10 g, 0.0152 mol, 75.8%). (Found: C, 72.36; H, 3.77%. C48H30012 requires (2, 72.18; H, 3.76%). 'H NMR (CDCl,, 400 MHz) 6 7.23 (d, 8.4 Hz, 6H, ArH), 7.29 (m, 3H, ArH), 7.44 (m, 12H, ArH), 8.33 (d, 8.8 Hz, 6H, ArH), 9.29 (s, 3H, ArH). 13C NMR (CDCl,, 400MHz) 6 121.61, 121.82, 126.01 (all aromatic C-H), 127.75 (aromatic C-R), 129.52 (aromatic C-H), 130.94 (aromatic C-R), 131.99, 136.37 (both aromatic C-H), 150.76, 154.45 (both aromatic C-0), 162.59, 164.19 (both C=O).The spectrum and assignments are shown in Fig. 1. v,,Jcm-' 3065.9, 1734.7, 1591.8, 1502.8. 5-Acetoxyisophthalic Acid To a stirred solution of 5-hydroxyisophthalic acid I 100.00 g, 0.59 mol) in aqueous sodium hydroxide (11, 2.5 moll- ') cooled in an ice-water bath, was added acetic anhydride (200 ml) slowly. Stirring was continued for 2 h, upon which the flask was shaken for 10min and the contents acidified to pH 1 using concentrated hydrochloric acid. The white slurry was filtered off and the filtrate extracted with ethyl acetate (6 x 300 ml). A further portion of ethyl acetate (900 ml) was added to this and the filtered residue was dissolved in it.The resultant solution was washed with water (5 x 500 ml) and the combined aqueous washings extracted with ethyl acetate (500 ml). The organic portions were combined, dried (MgS04), the solvent removed by evaporation and the residue dried under vacuum at 80 "C for 4 h. to yield a white powdery solid Table 1 Physical properties of dendrimers [7], [16] and [19] relative molecular dendrimer mass 798c71 c 161 1878 c 191 2238 solubility(chloroform, 25 "C)/ g 1-' 297 156 174 2% wt. loss mp (DSC)/OC A€usHIJ g-' 4 TG)/"C 190 71 278 152 20 389 136 13 405 (122.56 g, 0.547 mol, 99.7%). Mp 246-247 "C (lit. 238-240 "C). 'H NMR (C2H6]acetone, 200 MHz) 6 2.35 (s, 3H, CH,), 8.00 (d, 1.52 Hz, 2H, ArH), 8.56 (t, 1.52 Hz, lH, ArH).I3C NMR (CZH6]acetone, 200 MHz) 6 21.30 (CH,), 128.44 (aromatic C-H), 128.89 (aromatic C-H), 133.73 (aromatic C-R), 152.46 (aromatic C-0), 166.50 (ArCO,H), 170.06 (COCH,). v,,Jcm-': 3100-2600, 1770.4, 1693.8. 5-Acetoxyisophthaloy1 Dichloride An intimate mixture of 5-acetoxyisophthalic acid (98.93 g, 0.492 mol) and phosphorus pentachloride (213.2 g, 1.024 mol) in a flask fitted with a reflux condenser and gas absorption device was warmed gently with a heat gun to initiate the reaction and shaken occasionally until the vigorous evolution of hydrogen chloride had ceased. To ensure complete reaction, the reaction mixture was stirred for a further 1h at room temperature to yield a pale yellow homogeneous oil.After removal of phosphorus oxychloride by distillation at atmospheric pressure, the residue was distilled at reduced pressure (132-134 "C, 0.3 mmHg) to produce a clear oil that yielded a white crystalline solid (1 13.75 g, 0.436 mol, 88.6%) on cooling. Mp 51.5-52.5 "C. 'H NMR (c2H6]acetone, 200 MHz) 6 2.37 (s, 3H, CH,), 8.28 (s, 2H, ArH), 8.65 (s, lH, ArH). 13C NMR ([2H6]acetone, 200 MHz) 6 21.29 (CH,), 131.33 (aromatic C-H), 132.03 (aromatic C-H), 136.44 (aromatic C- R), 153.07 (aromatic C-0), 167.46 (COCl), 169.78 (COCH,). v,aJcm-l; 3092.6, 3028.7, 1774.7. Protected Second-generation Wedge, [51-OAc To a suspension of 5-acetoxyisophthaoyl dichloride (68.02 g, 0.261 mol) in pyridine (1 1) were added phenyl 4-hydroxy- benzoate ( 114.00 g, 0.533 mol), 4-dimethylaminopyridine (1.50 g, 0.012 mol) and dichloromethane (330 ml).After the mixture had been stirred at room temperature for 36 h, dichloromethane (1.6 1) was added and the solution washed with aqueous hydrochloric acid (12 x 600 ml, 10% v/v) and aqueous sodium hydroxide (12 x 600 ml, 1.0 mol 1-'), dried (MgSO,), the solvent removed by evaporation and the residue dried under vacuum to yield a white powdery solid (149.52 g, 0.243 mol, 93.0%). Mp 194.5-196.5 "C. 'H NMR (CDCI,, 400 MHz) 6 2.40 (s, 3H, CH,), 7.23 (m, 4H, ArH), 7.29 (m, 2H, ArH), 7.43 (m, 8H, ArH), 8.24 (d, 1.6 Hz, 2H, ArH), 8.32 (d, 8.4 Hz, 4H, ArH), 8.91 (t, 1.6 Hz, lH, ArH). 13C NMR (CDCl,, 400 MHz) 6 20.95 (CH,), 121.62, 121.83, 125.97 (all aromatic C-H), 127.58 (aromatic C-R), 128.71, 129.09, 129.50 (all aromatic C-H), 131.27 (aromatic C-R), 131.93 (aromatic C-H), 150.78, 151.07, 154.56 (all aromatic C-0), 162.72, 164.24 (both aromatic C=O), 168.89 (OCOCH,).v,,Jcm-': 3078.6, 1773.3, 1743.8, 1590.5, 1503.1, 746.4. Second-generation Wedge, [5]-OH To a mixture of aqueous hydrochloric acid (700 ml, 10% v/v) and THF (2.1 1) was added [5]-OAc (147.73 g, 0.240 mol) and the solution refluxed for 18 h. On cooling, the THF was removed by evaporation and the residue extracted with ethyl acetate (4 x 500 ml), dried (MgSO,) and the solvent removed by evaporation. The residue was recrystallised from hot toluene, washed with hexane and dried under vacuum to yield a fine white powder (119.34 g, 0.208 mol, 86.6%).Mp 202.0-205.5 "C. 'H NMR (C2H6] acetone, 400 MHz) 6 7.33 (m, 6H, ArH), 7.49 (m, 4H, ArH), 7.59 (d, 8.8 Hz, 4H, ArH), 7.98 (d, 1.6 Hz, 2H, ArH), 8.31 (d, 9.2 Hz, 4H, ArH), 8.49 (t, 1.6 Hz, lH, ArH), 9.50 (broad, IH, OH). I3C NMR (C2H6]acetone, 400 MHz) 6 122.57, 122.77, 123.28, 123.36, 126.75 (all aromatic C-H), 128.38 (aromatic C-R), 130.32 (aromatic C-H), J. MATER. CHEM., 1994, VOL. 4 132.22 (aromatic C-R), 132.47 (aromatic C-H), 152.1 1, 156.08, 159.03 (all aromatic C-0), 164.22, 164.79 (both aromatic C=O). v,,Jcm-': 3386.1, 3071.1. 1736.7, 1708.8, 1601.2, 1498.0, 744.7. Second-generation Dendrimer, [161 To a stirred solution of [Sl-OH (4.50 g, 0.00784 mol) in dichloromethane (30 ml) and N,N-dimethylaniline ( 1.5 ml) was added benzene-1,3,5-tricarbonyl trichloride (0.58 g, 0.002 18 mol) and the mixture stirred at room temperature for 40 h.On addition of dichloromethane (60 ml), the solution was washed with aqueous hydrochloric acid solution (3 x 50 ml, 10% v/v) and brine (2 x 50 ml). After the mixture had been dried (MgSO,), the solvent was removed by evapor- ation and the residue purified by column chromatography [dichloromethane-1 % ethyl acetate/silica (Merck silica gel 60)] followed by recrystallisation (1: 1 ethanol-ethyl acetate) to yield a white powder (1.01 g, 0.000 538 mol, 24.7%). (Found: C, 70.61; H, 3.46%. ClllH66030 requires C, 70.93; H, 3.51%). 'H NMR (CDCl,, 400 MHz) 6 7.22 (d, 8.8 Hz, 12H, ArH), 7.29 (m, 6H, ArH), 7.44 (m, 24H, ArH), 8.32 (d, 8.8 Hz, 12H, ArH), 8.45 (d, 1.6 Hz, 6H, ArH), 9.01 (t, 1.2 Hz, 3H, ArH), 9.37 (s, 3H, ArH).13C NMR (CDCl,, 400 MHz) 6 121.63, 121.84, 126.05 (all aromatic C-H), 127.74 (aromatic C-H), 128.60, 129.55, 129.73 (all aromatic C-H), 130.74, 131.70 (both aromatic C-R), 132.01, 136.72 (both aromatic C-H), 150.78, 150.84, 154.51 (all aromatic C-0), 162.60 (2 x aromatic C=O), 164.23 (aromatic C=O). The spectrum and assignments are shown in Fig. 1 and the hetcor spectrum in Fig. 2. v,Jcm-': 3073.6, 1739.3, 1599.9, 1503.4, 742.0, Protected Extended Second-generation Wedge, [61-OAc To a stirred solution of 4-acetoxybenzoyl chloride (5.42 g, 0.0273 mol) in pyridine (250 ml) were added [Sl-OH (12.50 g, 0.0218 mol), dichloromethane (80 ml) and 4-dimethyl-aminopyridine (0.18 g, 0.0015 mol). After this mixture had been stirred at room temperature for 48 h, dichloromethane (250 ml) was added and the solution washed with aqueous hydrochloric acid (6 x 300 ml, 10% v/v) and aqueous sodium hydroxide (9x300m1, 1.0mol 1-I).After the mixture had been dried (MgSO,), the solvent was removed by evaporation and the residual oil dried under vacuum to yield a fine white powder (13.34 g, 0.0181 mol, 83.1%). Mp 75.0-76.0 "C. 'H NMR (CDCl,, 400 MHz) 6 2.36 (s, 3H, CH,), 7.22 (m, 4H, ArH), 7.30 (A,4H, ArH), 7.43 (m, 8H, ArH), 8.28 (d, 8.8 Hz, 2H, ArH), 8.32 (d, 8.8 Hz, 4H, ArH), 8.36 (d, 1.6 Hz, 2H, ArH), 8.96 (t, 1.6 Hz, lH, ArH). I3CNMR (CDCl,, 400 MHz) 6 21.18 (CH,), 121.66, 121.88, 122.14 (all aromatic C-H), 125.91 (aromatic C-R), 126.01 (aromatic C-H), 127.62 (aromatic C-R), 128.84, 129.29, 129.54 (all aromatic C-H), 131.41 (aromatic C-R), 131.98, 132.00 (both aromatic C-H), 150.82, 151.35, 154.62, 155.33 (all aromatic C-0), 162.77, 163.94, 164.29 (all aromatic C=O), 168.69 (OCOCH,).vmaX/cm-': 3074.3, 1738.3, 1601.2, 1503.7, 742.1. Extended Second-generation Wedge, [6]-OH To a solution of [6]-OAc (97.51 g, 0.132 mol) in THF (1.5 1) was added aqueous hydrochloric acid (0.5 1, 10% v/v) and the mixture refluxed for 24 h. When the mixture had been cooled water (300 ml) was added and the THF removed by evapor- ation. The residue was extracted with ethyl acetate (3 x 400 ml) and the combined organic layers washed with aqueous hydro- chloric acid (3 x 300 ml, 10% v/v), dried (MgSO,) and the solvent removed by evaporation.The residual oil was dried under vacuum to give a white solid that was recrystallised J. MATER. CHEM., 1994, VOL. 4 from toluene, washed with hexane and dried under vacuum (120 "C) overnight to yield a white powdery solid (79.44 g, 0.114 mol, 86.7%). Mp 215.5-216.0 "C. 'H NMR (C2H6]acetone, 400 MHz) 6 7.04 (d, 8.8 Hz, 2H, ArH), 7.32 (m, 6H, ArH), 7.49 (m, 4H, ArH), 7.62 (d, 8.8 Hz, 4H, ArH), 8.14 (d, 8.8 Hz, 2H, ArH), 8.31 (d, 8.8 Hz, 4H, ArH), 8.44 (d, 1.6 Hz, 2H, ArH), 8.86 (t, 1.6 Hz, lH, ArH), 9.54 (broad, lH, OH). 13C NMR (C2H6]acetone, 400 MHz) 6 116.38 (aromatic C-H), 116.47 (aromatic C-R), 122.76, 123.26, 126.74 (all aromatic C-H), 128.45 (aromatic C-R), 129.20, 129.63, 130.31 (all aromatic C-H), 132.30 (aromatic C-R), 132.47, 133.53 (both aromatic C-H), 152.07, 152.78, 155.93 (all aromatic C-0), 163.64 (aromatic C=O), 163.75 (aromatic C-OH), 164.76, 165.02 (both aromatic C=O).vmaX/cm-': 3392.1, 3072.5, 1739.3, 1591.0, 1503.5, 744.0. Extended Second-generation Dendrimer, [ 191 To a stirred solution of [6]-OH (1.55 g, 0.00223 mol) in dichloromethane ( 12 ml) and N,N-dimethylaniline (0.4 ml) was added benzene-1,3,5-tricarbonyl trichloride (0.169 g, 0.000 636 mol) and the mixture stirred at room temperature for 40 h. On addition of dichloromethane (30 ml), the solution was washed with aqueous hydrochloric acid solution (5 x 50 ml, 10% v/v) and brine (2 x 50 ml).The organic layer was dried (MgS04) and the solvent was removed by evapor- ation. The residue was purified by column chromatography ([dichloromethane-1 %ethyl acetate/silica (Merck silica gel 60)] to produce a white solid that was recrystallised from 1: 1 ethanol-ethyl acetate then dried under vacuum (120 "C, over- night) to yield a white powder (0.24 g, 0.000 107 mol, 16.9%). (Found: C, 68.94; H, 3.40%. C13&17@36 requires: C, 70.78; H, 3.49%). 'H NMR (CDCl,, 400MHz) 6 7.24 (d, 8.4 Hz, 12H, ArH), 7.30 (m, 6H, ArH), 7.45 (m, 24H, ArH), 7.53 (d, 8.4 Hz, 6H, ArH), 8.34 (d, 8.4 Hz, 12H, ArH), 8.40 (m, 12H, ArH), 9.00 (s, 3H, ArH), 9.33 (s, 3H, ArH). 13C NMR (CDCl,, 400 MHz) 6 121.76, 121.98, 122.25, 126.14 (all aromatic C-H), 126.82, 127.78 (both aromatic C-R), 128.92, 129.47, 129.66 (all aromatic C-H), 131.07, 131.59 (both aromatic C-R), 132.10, 132.38, 136.61 (all aromatic C-H), 150.92, 151.40, 154.71, 155.10 (all aromatic C-0), 162.62, 162.86, 163.91, 164.38 (all aromatic C=O).The spectrum and assignments are shown in Fig. 1. vmax/cm-l: 3071.9, 1738.7, 1599.8, 1504.1. Protected Third-generation Wedge, [ 131-OAc To a suspension of 5-acetoxyisophthaoyl dichloride (2.68 g, 0.0103 mol) in pyridine (250 ml) were added [6]-OH (15.00 g, 0.0216 mol), 4-dimethylaminopyridine (0.15 g, 0.0012 mol) and dichloromethane (80ml). After the mixture had been stirred at room temperature for 4 days, dichloromethane (250 ml) was added and the solution washed with aqueous hydrochloric acid (15 x 200 ml, 10% v/v) and aqueous sodium hydroxide (15 x 200 ml, 1.0 mol 1-'), dried (MgSO,), the solvent removed by evaporation and the residue drietl under vacuum (90°C, 4 h) to yield a white powdery solid (7.11 g, 0.00451 mol, 41.8%).'H NMR (CDCl,, 400 MHz) 6 2.40 (s, 3H, CH,), 7.24 (m, 8H, ArH), 7.29 (m, 4H, ArH), ".44 (m, 20H, ArH), 8.25 (d, 1.6 Hz, 2H, ArH), 8.32 (d, 8.4 Hz, 8H, ArH), 8.36 (d, 8.8 Hz, 4H, ArH), 8.39 (d, 1.6 Hz, 4H, ArH), 8.92 (t, 1.6 Hz, lH, ArH), 8.97 (t, 1.6 Hz, 2H, ArH). 13(: NMR (CDCI,, 400 MHz) 6 20.97 (CH,), 121.62, 121.84, 122.13, 125.99 (all aromatic C-H), 126.46, 127.60 (both aromatic C-R), 128.80 (2 x aromatic C-H), 129.17, 129.37, 129.51 (all aromatic C-H), 131.18, 131.42 (both aromatic C-R) 131.95, 132.16 (both aromatic C-H), 150.76, 151.12, 151.28.154.57, 155.08 (all aromatic C-0), 162.61, 162.72, 163.81, 164.25 (all aromatic C=O), 168.91 (OCOCH,). vmax/cm-': 3075.9, 1740.4, 1600.5, 1503.4, 742.8. Conclusion The synthesis of aryl ester dendrimers with flexible. spacer units has been achieved via a convergent process. All niaterials are soluble in conventional organic solvents. The der idrimers form miscible blends with PET, the properties of wliich will form the basis of future publications. We gratefully acknowledge the provision of an SER(I Quota award (N.M.S.) and the help of Miss S. C. E. Backson, Mrs. J. M. Say and Dr. A. M. Kenwright in some aspects of the characterisation of these materials. References D. A. Tomalia, A. M. Naylor and W. A. Goddard 111, Angefii. Chem., Int. Ed. Engl., 1990,29, 138. D. A. Tomalia, H. Baker, J. R. Dewald, M. Hall, C. Kallos, S. Martin, J. Roeck, J. Ryder and P. Smith, Polym. J., 1985, 17, 117. G. R. Newkome, Z. Yao, G. R. Baker and V. K. Gupt.1, J. Org. Chem., 1985, 50, 2003. C. J. Hawker and J. M. J. Frechet, J. Am. Chem. Soc., 990, 112, 7638. T. M. Miller, E. W. Kwock and T. X. Neenan, Macronolecules, 1992,25,3143. C. J. Hawker and J. M. J. Frechet. J. Am. Clzem. Soc., 992, 114, 8405. J. Quick and J. K. Crelling, J. Org. Chem., 1978,43, 155. Paper 4/01367K; Received 8th Mu *ch,1994

ISSN:0959-9428    

DOI:10.1039/JM9940401159

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(8), 1167-1172 Curing Reactions in Acetylene-terminated Resins Part 5. t-Cyclotrimerization versus Linear Polyene Formation in the Catalysed Cure of Ethynylaryl-terminated Monomers William EmDouglas** and Andrew S. Overend Department of Industrial, Organic and Polymer Chemistry, Kingston Polytechnic, Penrhyn Road, Kingston-upon-Thames, Surrey, UK KT1 2EE Structural differences in the polymers obtained by catalysed cure of the ethynylaryl-terminated monomer [1,4-(1,3-HC-CC6H4CH,0)C6H4]2CMe2 (1) could not be detected by IR or NMR spectroscopy. However, a study of the solvent-free catalysed polymerization of the model monomer, phenylacetylene, showed that the extent of cyclotrimeriz-ation decreased in the order (y-Cp)Co(CO),>>(y-Cp),Ni z(PPh,),NiCI,>> (PPh3)2PdCI, with an accompanying iicrease in the degree of linear polyene formation, suggesting that this is so also for the catalysed cure of 1.High-performance resins formed from acetylene-terminated monomers (ATMs) are currently being developed to replace, for example, epoxies, which suffer from an undesirable reduction in glass-transition temperature when used under hot, wet This paper is part of a series describing the effect of catalysts on the curing reactions of the two main groups of ATMs, those terminated by aryl prop-2-ynyl ether and those by ethynylaryl groups. In Part 4,4 we have shown that, in the case of aryl prop-2- ynyl ether ATMs, the use of catalysts gives rise to quite different crosslink structures than in the absence of catalysts, and that by judicious choice of catalyst cyclotrimerization and/or linear polymer formation can be obtained. Here, we give the results of an IR and NMR study into the catalysed polymerization of ethynylaryl-terminated ATMs: the thermal properties of the fully cured resins were reported previ~usly.~ Some of the preliminary results concerning polymerization of phenylacetylene in the presence of nickelocene have been communicated.6 The uncatalysed cure of ethynylaryl-terminated ATMs takes place via a free-radical reaction resulting in a network whose crosslink sites are linear conjugated polyenes formed from six to eight ethynyl groups7 together with some cyclotrimerization of acetylene end-group~.~?~ Many transition-metal complexes are known to catalyse acetylene reactions such as cyclo-trimerization, cyclotetramerization and linear polyene forma- tion," and their use in the cure of ATMs might therefore be expected to affect the structure and properties of the resulting resins.However, few such studies have been reported. (PPh,),NiCl, has been found to lower the cure temperature of ethynylaryl-terminated monomers sufficiently (< 177 "C) for the resins to be used as adhesives for A1 alloys." The effect of high concentrations (20 mol% ethynyl group) of (PPh,)2Ni(C0)2 on the processing of ethynylaryl-terminated polyimides has also been examined.12 Two of the catalysts which we had originally reported as being active13 have been used since in the cure of aryl prop-2-ynyl ether ATMs, namely cobaltocene (which was found to give rise to cyclotrimeriz- ation)14 and bis( tripheny1phosphine)palladium dich10ride.l~ Experimental IR spectra (CsI discs) were recorded by use of a Perkin-Elmer 728 spectrometer connected to a Perkin-Elmer 360 data -f Part 4:W.E. Douglas and A. S. Overend, J. Muter. Chem., 1993, 3, 1019. $ Present address: CNRS UM 44, Case 007, USTL, Place E. Bataillon, 34095 Montpellier CCdex 5, France. station. 'H NMR spectra were run on a Bruker WP-80-SY spectrometer operating at 80.13 MHz or a Perkin-Elmer R32 instrument at 90 MHz. Mass spectra were obtained by use of an AE1 MS9 mass spectrometer. Molecular weights were determined by VPO in toluene at 45°C using a Knauer instrument calibrated with benzil.Elemental analyses were carried out by Butterworth Laboratories, Twicker, ham. The catalysts (~-cp)~Ni,(y-Cp)Co(CO), (technical grade in dicyclopentadiene; this particular batch assayed by Aldrich at 50%), and (PPh,),RhCl were commercial samples (Aldrich) and were used as received except nickelocene, which was resublimed before use. (PPh,),NiCl, was prepared from NiC1,-6H20 and PPh, in glacial acetic acid. The ethynylaryl ATM [I$( 1,3-HC-CC6H4CH,0)C6H~],cMe,(1) and samples of fully cured 1 for IR studies were prepared as pre- viously described5 (the IR absorbances of 1 are listzd below). v PjyQo1 1 Phenylacetylene (Aldrich) was redistilled under reduced pressure.When only a proportion of the reaction mixture was worked up, the overall percentage yield is given icalculated from the isolated yield for the sample taken), All reaction products were recovered in essentially their entirety, the sum of the individual yields approximating to 100% iii all cases. 1,2,4-Triphenylbenzene exists in two forms melting at 100"C and 119-120 OC;16 the mp of 1,3,5-triphenylbenzene is 172-173 OC.I7 IR Spectrum of 1 vmax/cm-': 3290s, 3060w, 3030w, 2980m, 2970111, 2950m, 2920m, 2870m, 2100w, 1885w( br), 1800vw, 1605m, 1580m, 1505s, 1480m, 1460m, 1440w, 1430m, 1410vw, 13&0s, 1360w, 1310w, 1285m, 1235s, 1180s, 1155w, 1115w, 1095w, 1085w, 1030s, 1020s, 970vw, 960vw, 945w, 930vw, 910w, 895m, 885m, 840s, 820s, 810m, 785m, 765m, 735w, 690m, 640m, 6:30m, 600m. (q-Cp)Co(CO),-Catalysed Polymerization of Pheny lacetylene To degassed phenylacetylene (3 g, 29.4 mmol) under N2 was added (y-Cp)Co(CO), (40 p1 of 50% solution in dicyclo- pentadiene, 0.11 mmol) and the mixture was heated at 140 "C for 4 h.A portion (0.89 g) of the resulting polymerized material was chromatographed on silica gel. Elution with 80 :20 v/v n-hexane-dichloromethane gave unchanged phenylacetylene (0.16g, 18%) followed by a white solid (0.68 g, 76%), the latter being a mixture of 1,2,4- and 1,3,5-triphenylbenzene with mp 132-136°C. (Found: C, 94.04; H, 5.96%. Calc. for C24H18: C, 94.08; H, 5.92%.) IR spectrum vmax/cm-' : 3080m, 3060m, 3025m, 1950w(br), 1880w(br), 18lOw(br), 1755w(br), 1595m, 1575w, 1495m, 1470m, 1440m, 1410w, 1390w, 1180w, 1155w, 1075m, 1030w, 1010m, lOOOw, 990w, 920w, 910vw, 900m, 875w, 845m, 780m, 765s, 750m, 740s, 715m, 705s.'H NMR, 6, (solvent CDCI,; standard TMS): 7.10-7.25 (1.00 H, m, arom.), 7.25-7.95 (1.73 H, m, arom.). (q-Cp),Ni-Catalysed Polymerization of Phenylacetylene To degassed phenylacetylene (3 g, 29.4 mmol) under N, was added (q-Cp),Ni (4.5 mg; 2.38 x lop5 mol) and the mixture was heated at 115 "C for 6 h. A solution of the crude product in 30 ml of dichloromethane was added dropwise to 300 ml of methanol, thus precipitating an orange polymer which was separated by filtration, washed thoroughly with methanol and dried. The precipitation pro- cedure was repeated and the product was dried under vacuum at 60°C to constant weight (1.17 g; 39%).The 'H NMR [Fig. l(u)] and IR spectra [Fig. 2(a)] showed the polymer to be trans-cisoidal poly( phenylacetylene) (see Discussion). M, 1600 g mol-', DP, 15.7. After removal of solvent from the combined filtrates, a portion (0.78 g) of the methanol-soluble material was chroma- tographed on silica gel. Elution with 80:20 v/v n-hexane-dichloromethane afforded unchanged phenylacetylene (0.10 g; I 8 I 7 I 6 L 8 Fig. 1 'H NMR spectra (90 MHz) of trans-cisoidal poly(pheny1ace-tylene) from polymerization of phenylacetylene in the presence of (a) (q-Cp),Ni, (b)(PPh,),NiCl, and (c) (PPh,),PdC12 J. MATER. CHEM., 1994, VOL. 4 1 6 3000 2000 1400 800 wavenumberkm-' Fig.2 IR spectra of trans-cisoidal poly( phenylacetylene) from poly- merization of phenylacetylene in the presence of (ti) (q-Cp),Ni, (h) (PPh,),NiCl, and (c) (PPh,)2PdC12 8%) followed by white crystals (0.31 g, 24%), the latter being a mixture of 1,2,4- and 1,3,5-triphenylbenzene with mp 122-126°C. (Found: C, 94.20; H, 5.80%. Calc. for CZ4Hl8: C, 94.08; H, 5.92%.) IR spectrum vmax/cm-' : 3080m, 3060m, 3020m, 1950w(br), 1880w(br), 18lOw(br), 1755w( br), 1595m, 1575w, 1495m, 1470m, 1440m, 1410w, 1390w, 1180w, 1155w, 1075m, 1030w, 1010m, 990w, 920w, 900m, 875w, 845m, 780m, 765s, 750w, 710m, 715m, 705s. 'H NMR, BH (solvent CDC1,; standard TMS): 7.10-7.25 (1.00 H, m, arom.), 7.25-7.95 (1.14 H, m, arom.). Finally, elution with 60:40 v/v n-hexane-dichloromethane gave a yellow solid (0.38 g; 30%), this being a mixture of low- molecular-weight linear oligomers of phenylacet ylene. ( Found: C, 93.98; H, 6.02%, Calc.for C24Hl,: C, 94.08; H, 5.92%.) IR spectrum vmax/cm-' :3080m, 3060m, 3020m, 2925w, 2855w, 2250vw, 1950w( br), 1870w( br), 1800w( br), 1750w( br), 1625w( br), 1595m, 1570w, 1490s. 1445m, 13XOvw, 1330vw, 1265w, 1220w, 1 NOW, 1160w, llOOw, 1075w, 1030w, lolow, ~~OVW,910~, 885~, 850~, 755~, 740m, 695s. 'H NMR, 8, (solvent CDCl,; standard TMS) :6.5-6.9 ( 1 H, m, olefinic), 7.0-7.9 (5 H, m, arom.). M, 460 g mol-', DP, 4.5. (PPh,),NiCl,-Catalysed Polymerization of Phenylacetylene To degassed phenylacetylene (3 g, 29.4 mmol) under N, was added (PPh3)2NiC12 (15.6 mg; 2.38 x mol) and the mix- ture was heated at 140°C for 4 h.A solution of the crude product in 30 ml of dichloromethane was added dropwise to 300 ml of methanol, thus precipitating a pale-brown polymer, which was separated by filtration, washed thoroughly with methanol and dried. The precipi- tation procedure was repeated and the product was dried under vacuum at 60°C to constant weight (0.88 g; 29%). The 'H NMR [Fig. l(b)] and IR spectra [Fig. 2(h)] showed the polymer to be trans-cisoidal poly ( phenylacetylene) (see Discussion). M, 1100 g mol-', DP, 10.8. After removal of solvent from the combined filtrates, a portion (0.72 g) of the methanol-soluble material was chroma- tographed on silica gel. Elution with 80: 20 v/v n-hexane-dichloromethane afforded unchanged phenylacetylene (0.22 g; J.MATER. CHEM., 1994, VOL. 4 22%) followed by white crystals (0.26 g, 26%), the latter being a mixture of 1,2,4- and 1,3,5-triphenylbenzene with mp 124-128°C (Found: C, 94.32; H, 5.68%. Calc. for C24H18: C, 94.08; H, 5.92%.) IR spectrum identical to that for the corresponding material isolated in the case of the (q-Cp),Ni- catalysed polymerization of phenylacetylene. 'H NMR, 6, (solvent CDCI,; standard TMS) :7.10-7.25 (1.00 H, m, arom.), 7.25-7.95 (1.22 H, m, arom.). Finally, elution with 60 :40 v/v n-hexane-dichloromethane gave a yellow solid (0.18 g; l8%), this being a mixture of low- molecular-weight linear oligomers of phenylacetylene. (Found: C, 94.56; H, 5.44%. Calc. for C24H18: C, 94.08; H, 5.92%.) IR spectrum identical to that for the corresponding material isolated in the case of the (q-Cp),Ni-catalysed polymerization of phenylacetylene. 'H NMR, 6, (solvent CDC1,; standard TMS): 6.5-6.9 (1 H, m, olefinic), 7.0-7.9 (5 H, m, arom.).M, 490 g mol-', DP, 4.8. (PPh3),PdC1,-Catalysed Polymerization of Phenylacetylene To degassed phenylacetylene (3 g, 29.4 mmol) under N, was added (PPh,),PdCl, (16.7 mg; 2.38 x lop5mol), and the mix- ture was heated at 130°C for 5 h. A solution of the crude product in 30 ml of dichloromethane was added dropwise to 300 ml of methanol, thus precipitating a brown polymer, which was separated by filtration, washed thoroughly with methanol and dried. The precipitation pro- cedure was repeated and the product was dried under vacuum at 60 "C to constant weight (2.59 g; 86%). The 'H NMR [Fig.l(c)] and IR spectra [Fig. 2(c)] showed the polymer to be trans-cisoidal poly(phenylacety1ene) (see Discussion). [Found: c, 93.95; H, 6.05%. Calc. for (C8H6),: C, 94.08; H, 5.92Y0.1 M, 1850 g mol-', DP, 18.1. After removal of solvent from the combined filtrates, the brown methanol-soluble material was chromatographed on silica gel. Elution with 80 :20 v/v n-hexane-dichloromethane afforded as the only other products unchanged phenylacety- lene (0.2 g; 7%) followed by white crystals (0.11 g, 4%) of 1,3,5-triphenylbenzene, mp 170-171 "C. (Found: C, 94.03; H, 5.97%. Calc. for C24H18: C, 94.08; H, 5.92%.) IR spectrum v,,,/cm-': 3080m, 3060m, 3025w, 1950w( br), 1880w(br), MOW( br), 1755w(br), 1595m, 1575w, 1500m, 1410m, 1310w, 1155w, 1075w, 1030w, 910w, 890vw, 875m, 765s, 750s, 700s.'H NMR, 6, (solvent CDC1,; standard TMS) :7.25-7.90 (m; arom.). MS (70 eV): m/z 306 (Mf). Results and Discussion IR and NMR Spectra of Polymers from 1 [1,4-(1,3-HC~CC6H4CH20)C6H,],CMe,(l),the ethynyla- ryl ATM, and samples of 1 fully cured in the presence of various catalysts were prepared as previously de~cribed.~ The polymerization enthalpies suggest that crosslinking occurs by cyclotrimerization in the presence of (y-Cp)Co(CO),, but predominantly by non-aromatic conjugated linear polyene formation with the other catalyst^.^ In principle, the IR spectra should reflect these differences.Thus, from the known pos- itions of the CH out-of-plane deformations for 1,2,4- and 1,3,5-triphenylbenzene,ls it can be expected that 1,2,4-cyclotrimerization would give rise to new absorbances at 900 and 845 cm-' and 1,3,5-cyclotrimerization to a new band at 875 cm-'. On the other hand, from IR data for cis- and trans- poly( phenylacetylene)," conjugated linear polyenes with a cis structure would be expected to show absorbances at 740, 895 and 1380cm-' whereas those with a trans configuration should possess bands at 922, 970 and 1265 cm-'. In fact, the IR spectra (Fig. 3) of the crosslinked resins are all very similar because absorbances originating in the monomer at 1380, 1235, 970,930, 895, 885, 840 and 735 cm-' (see Experimental) obscure any new bands arising in these regions.However, the absence of v(-C-H) and v(C=C) stretches in all cases shows that the resins contain no unreacted acetylene groups. Unlike the case of aryl prop-2-ynyl ether ATMs rn here the propargyl CH20 group could be used as a probe,4 the NMR spectra of both the partly and fully cured resins formed from 1 were of no help in determining crosslink structures since all new resonances fall in regions of the spectra where peaks are already present in the monomer. Previously, in an F'TIR and solid-state CPMAS NMR study of a fully cured ethynylaryl ATM,,' it proved difficult to detect different crosslink struc- tures. However, in a more recent CPMAS NMR investigation with resins obtained from isotopically labelled monomers of the ethynylaryl type, resonances from new aromatic groups were observed.' The investigation was therefore pursued by studying the solvent-free catalysed polymerization of phenylacetylene as a model monomer for 1.Unlike 1, phenylacetylene contains only a single acetylene group, and hence the polymerization products are soluble and can be separated and characterized. Catalysed Polymerization of Phenylacetylene in the Absence of Solvent The solution polymerization of phenylacetylene in the pres- ence of a wide variety of catalysts has been extensively studied previously. Here, we report the results of an investigation into the catalysed bulk polymerization of phenylacetylene under I 4 10 3000 2000 1400 800 wavenumbedcm-' Fig.3 IR spectra (CsI discs) of 1 fully cured in the presence of (a)no catalyst, (b) (~pCp)Co(C0), (0.4 mol% ethynyl group), (c) (q-Cp),Ni (0.08 mol% ethynyl group), (d) (PPh,),NiCI, (0.08 rn01':/~ ethynyl group) and (e) (PPh,),PdCI, (0.08 mol% ethynyl group) the same conditions as we used for the preparation of fully cured resins from 1.' The reaction conditions and results are summarized in Table 1. (4(r7-CP)CO(C0)2 The reaction mixture was separated by chromatography into unchanged monomer (18%) and a white solid (76%) which was found to be a mixture of 1,2,4- and 1,3,5-triphenylbenzene with mp 132-136°C. The 'H NMR spectrum showed only aromatic proton resonances at 6 7.10-7.95. In particular, there were no signals characteristic of linear alkenes in the 6 6.5-7.0 region.Comparison of the IR spectrum with those of 1,2,4- and 1,3,5-triphenylben~ene'~confirms that the material is a mixture of the two isomers. Thus, benzoidal out-of-plane C-H bending absorbances are present both at 845 and 900 cm-l for 1,2,4-triphenylbenzene and at 875 cm-' for the 1,3,5 isomer. No bands were observed in the 1610-1630 cm-' region for linear poly( phenylacetylene). The proportion of the two isomers may be estimated by 'H NMR from the relative intensities of the aromatic proton resonances in the S 7.1-7.25 and 6 7.25-7.9 regions. 173,5-Triphenylbenzene exhibits reson- ances only in the latter region (intensity 18H),," whereas the 1,2,4 isomer shows signals in both regions with intensities of 10H and 8H, Hence, from the measured integration ratio of 1:1.73 the ratio of 1,2,4- to 1,3,5-triphenylbenzene is 2: 1 (a 3: 1 ratio would be expected on statistical grounds).Thus, (y-Cp)Co(CO), gives rise to exclusive cyclotrimeriz- ation of phenylacetylene in the absence of solvent. In solution, (y-Cp)Co(CO), is known to cyclotrimerize acetylenes.22 Therefore, cyclotrimerization probably occurs also in the (q-Cp)Co(CO),-catalysed cure of 1, although thermal studies indicate5 that after gelation other non-catalysed crosslinking reactions also take place because of reduced chain mobility. (b)(V-CP),Ni Addition of methanol to a dichloromethane solution of the reaction mixture precipitated a methanol-insoluble orange polymer (39%) which elemental analysis showed to be pure poly( phenylacetylene) with M, = 1600, corresponding to a degree of polymerization of 15.7.The 'H NMR spectrum [Fig. l(a)] showing a broad resonance in the 6 6-8 region is typical of that for trans-cisoidal poly (phenyla~etylene).'~ Furthermore, the IR spectrum [Fig. 2(a)] [with no v(C-C) stretch] is essentially identical to that for trans-cisoidal poly( phenyla~etylene),'~ both showing bands characteristic of trans-poly(phenylacety1ene) at 912, 970 and 1265 cm-', and also an absorbance at 885 cm-' which is specific to cis-poly(phenylacetylene). The methanol-insoluble polymer was therefore trans-cisoidal poly( phenylacetylene). The methanol-soluble material was separated into three fractions by column chromatography.Unchanged phenyl- acetylene (8%) was eluted first followed by a white crystalline solid (24%) which, as discussed above for the (y-J. MATER. CHEM.. 1994, VOL. 4 Cp)Co(CO),-catalysed system, was shown by elemental analy- sis and IR and 'H NMR spectroscopy to be an 84 : 16 mixture of 1,2,4- and 173,5-triphenylbenzene. The final fraction was a yellow solid obtained in 30% overall yield (not 21% as previously incorrectly reported6) which elemental analysis showed to be poly(phenylacetylene), the M, of 460 corre- sponding to a degree of polymerization of 4.5. The IR spectrum showed a v(CzC) stretch at 2250cm-' [but no v(-C-H) absorbance] as well as bands characteristic of both cis-(885 and 740 cm-') and trans-poly(phenylacety1ene) (970 and 912 cm-').19 The 'H NMR spectrum exhibited resonances in the 6 6.5-6.9 alkene region as well as aromatic signals, the integration ratio being 1:5.The yellow solid was therefore a mixture of low-molecular-weight linear oligomers of phenylacetylene. Acetylenes react with nickelocene to form two types of air- stable compound; green binuclear acetylene-bridged 2 and red mononuclear 3 (Scheme l).23Formation of the latter complex is favoured by the presence of electron-withdrawing substitu- ents in the acetylene compound.23 The complexes are prepared by reaction in THF for 20-30 h at room temperat~re,,~ or in the case of the ethyne complex 2, in THF at 12 atm and 80 "C for 15 h.24 The ethyne complex 2 as well as nickelocene itself have been claimed to be active catalysts in the solution polymerization of acetylenes at 70 "C both at atmospheric pressure and under high pressure.25 The presence of an aromatic heterocyclic amine (e.g.pyridine), which forms a reactive complex with the nickel catalyst and can also act as solvent, is a necessary component in the process.25 Until the present study was undertaken,13 nickelocene alone had not been used as a catalyst for acetylene polymerization, although with F,CC=CCF3 it has been reported to give trace amounts of the cyclotrimer after 10 h at 358 K.26At 50°C in benzene for 25 h, 0.1-0.3 mol% (q-Cp),Ni.2A1Br3 catalyses the conversion of acetylenes into a mixture of cyclotrimers and linear polymer.27 However, under the same conditions no reaction was observed in the absence of A~BI-,.,~ We have found that under solvent-free conditions, nickelocene catalyses terminal-acetylene p~lymerization.'~ As reported here, with Q 2 Scheme 1 Table 1 Reaction conditions and products for the catalysed polymerization of phenylacetylene methanol-insoluble trans-cisoidal catalyst catalyst conc.(mol YO) polymerization T/OC t/h conversion (YO) poly (phen ylacetylene) yield (YO) DP," (rl-CP)CO(CO), 0.4 140 4 82 - - (Ph,Pj,PdCI, (rl-CPj,Ni (Ph3P)2NiCI, 0.08 0.08 0.08 130 115 140 5 6 4 93 92 78 86 39 29 18.1 15.7 10.8 methanol-soluble linear oligomers yield (YO) DP," 30 4.5 18 4.8 triphen ylbenzene ratio yield (YO) 1,2,4:1,3,5' 76 66134 24 84:16 26 81:19 4 0:100 A '--' entry indicates that no material of that type was isolated."Calculated from the value of M, determined by VPO. bDetermined by 'H NMR spectroscopy (see Discussion). J. MATER. CHEM., 1994, VOL. 4 phenylacetylene both cyclotrimerization and linear polyene formation occur, whereas in the case of aryl prop-2-ynyl ether ATMs only cyclotrimers and cyclotetramers are ~btained.~ We are at present investigating the reaction mechanism. The green colour observed initially may be due to the formation of the known complex 2 (R=H, R’=Ph).28 The product distribution found for phenylacetylene is con- sistent with the value of the enthalpy of polymerization of 1 measured by DSC,’ suggesting that crosslinking occurs pre- dominantly uia non-aromatic conjugated linear polyene for- mation, together with some cyclotrimerization to give new benzene rings. (c) (PPh3)2NiC12 Addition of methanol to a dichloromethane solution of the reaction mixture precipitated a methanol-insoluble pale brown polymer (29%) which elemental analysis showed to be pure poly(phenylacety1ene) with a value of M, of 1100, correspond- ing to a degree of polymerization of 10.8. As described above for the nickelocene-catalysed system, the ‘H NMR [Fig. l(b)] and IR spectra [Fig.2(b)] showed the methanol-insoluble polymer to be trans-cisoidd poly( phenylacetylene).” The methanol-soluble material was separated into three fractions by column chromatography.Unchanged phenyl- acetylene (22%) was eluted first followed by a white crystalline solid (26%) which, as discussed above for the (y-Cp)Co(CO),-catalysed system, was shown by elemental analy- sis and IR and ‘H NMR spectroscopy to be an 81 :19 mixture of 1,2,4- and 1,3,5-triphenylbenzene. The final fraction was a yellow solid (18% yield) which elemental analysis showed to be poly(phenylacetylene), the M, of 490 corresponding to a degree of polymerization of 4.8. As in the case of the nickel- ocene-catalysed system, the IR and ‘H NMR spectra showed the yellow solid to be a mixture of low-molecular-weight linear oligomers of phenylacetylene with the structure PhC=C-( PhC=CH),-H. In previous studie~,~~?~’ the (PPh,),NiCl,-catalysed poly-merization of phenylacetylene has been studied in refluxing benzene in air.After 12 h, the reaction mixture was found to contain 39% unchanged phenylacetylene, 24% cyclotrimers (83:17 mixture of 1,2,4- and 1,3,5-triphenylbenzene) and 4% methanol-insoluble linear poly( phenylacetylene) with M, =2090. (d)(PPh3)2PdCl, Addition of methanol to a dichloromethane solution of the reaction mixture precipitated a methanol-insoluble brown polymer (86%) which elemental analysis showed to be pure poly(phenylacety1ene) with a value of M, of 1850, correspond- ing to a degree of polymerization of 18.1. As described in (b) for the nickelocene-catalysed system, the ‘H NMR [Fig. 1 (c)] and IR spectra [Fig, 2(c)] showed the methanol-insoluble polymer to be trans-cisoidal poly( phenyla~etylene).’~ The methanol-soluble material in this case consisted of only two compounds, which were separated by column chromato- graphy; unchanged phenylacetylene (7%) was eluted first followed by a white crystalline solid (4%) identified as 1,3,5-triphenylben~ene.’~,’~ The present results are in good agreement with those from previous studies of the bulk polymerization of phenylacetylene in the presence of considerably higher concentrations of (PPh,),PdCl,; with 5 mol% catalyst for 5 h at 140 OC,I9 or in air with 5 or 0.2 mol% catalyst for 4 h at 140°C.31 In both cases, methanol-insoluble trans-cisoidal poly (phenylacetylene) was obtained together with a small proportion of 1,3,5-triphenylbenzene which, it was suggested, resulted from thermal cyclization and scission of the linear poly( phenyl- acetylene) chain rather than from Pd-catalysed cyclo-trimerization.” The value of the enthalpy of polymerization of 1 in the presence of (PPh,),PdCl, is consistent with crosslinking occurring predominantly via non-aromatic conjugated linear polyene f~rrnation,~ and the present results in the ciise of phenylacetylene support this mechanism.In a previous study into the polymerization of the aliphatic diethynylaryl-terminated ATMs HC-C(CH,),C -CH (n=2-5) in refluxing cyclohexane in the presence of (Ph,P)2Ni(CO), it was shown by using IR and other analytical techniques that depending on the value of n, formation of both aromatic cyclotrimers and conjugated linear polyalkene structures occurs.32 Conclusions The ability of the catalysts to promote cyclotrimerization of phenylacetylene in the absence of solvent decreases in the following order with a concomitant increase of linear poly( phenylacetylene) formation: z(Ph,P),NiCl, >>( PPh,),PdCl, The same sequence would thus appear to obtain fctr the crosslinking reactions occurring in the cure of 1, linear polyene structures predominating in the case of (PPh,),PdCl, and sub- stantial cyclotrimerization taking place with (y -Cp)Co( CO),.It is to be expected that these fundamental differences in chemical structure will affect the physical properties of the cured resins. In particular, resins cured in the presence of (y -Cp)Co( CO), should contain highly stable benzene crosslink sites.However, overall thermal stability of the resin may depend on the structure of the monomer itself rather than that of the crosslinks, as indeed is the case for the resins obtained by catalysed cure of l.5 Finally, note that although the catalysed polymerization of phenylacetylene is nearly complete for nickelocene and (PPh3),PdC1,, ca. 20% of the monomer remains unreacted in the cases of (y-Cp)Co(CO), and (Ph,P),NiCl, [for the (Ph,P),NiCl,-catalysed polymerization conducted in refl uxing benzene, as much as 40% of the phenylacetylene was recovered ~nchanged~~,~’].Therefore, for resins produced from 1 in the presence of the last two catalysts, at least 20% of the crosslinks may be expected to be of the linear polyene type resulting from the uncatalysed reaction of the remaining ace1 ylene groups in the post-cure stage.We thank the Royal Borough of Kingston-upon-Thamcs for a Research Assistantship awarded to A.S.O. References 1 C. Y-C. Lee, in Developments in Reinforced Plastics, ed. G. Pritchard, Elsevier, Barking, 1986, vol. V, pp. 121-150. 2 P. M. Hergenrother, in Encyclopaedia of Polymer Sciencx and Engineering, ed. H. F. Mark, N. M. Bikales, C. G. Overherger, G. Menges and J. I. Kroschwitz, Wiley, New York, 2nd edn. 1985, VO~.1, pp. 61-86. 3 V. A. Sergeev, Yu. A. Chernomordik and A. S. Kurapoj, Usp. Khim., 1984,53,518 (Russ. Chem. Rev., 1984,53,307). 4 W. E. Douglas and A. S. Overend, J.Muter. Chem., 1993,3,1019. 5 W. E. Douglas and A. S. Overend, Eur. Polym. J., 1993,29, 1513. 6 W. E. Douglas and A. S. Overend, J. Organomet. Chem.. 1993, 444, C62. 7 C. Y-C. Lee, 1. J. Goldfarb, T. E. Helminiak and F. E. Arnold, Natl. SAMPE Symp. Exhib. (Proc.) 28th (Muter. Pro( esses-Contin. Innovations), 1983,699. 8 M. D. Sefcik, E. 0. Stejskal, R. A. McKay and J. Scliaefer, Macromolecules, 1979,12,423. 1172 J. MATER. CHEM., 1994, VOL. 4 9 10 11 12 13 14 15 16 17 S. A. Swanson, W. W. Fleming and D. C. Hofer, Macromolecules, 1992.25, 582. J. P. Collman, L. S. Hegedus, J. R. Norton and R. G. Finke, Principles and Applicutions of Orgunotransition Metal Chemistry, University Science Books, Mill Valley, 2nd edn., 1987. L. G.Picklesimer, M. A. Lucarelli, W. B. Jones, T. E. Helminiak and C. C. Kang, Polym. Prep., 1981, 22, 97; M. A. Lucarelli, W. B. Jones Jr., L. G. Picklesimer and T. E. Helminiak, ACS Symp. Ser., 1982, 195, 237. T. Takeichi and J. K. Stille, Macromolecules, 1986, 19, 2093; 2108. W. E. Douglas and A. S. Overend, J. Organomet. Chem., 1986, 308, C14. V. A. Sergeyev, V. K. Shitikov, A. S. Kurapov and I. P. Antonova- Antipova, Vys. Soyed., 1989, A31, 1188 (Polym. Sci. USSR, 1989, 31,1300). A. P. Pigneri and R. S. Bauer, US Put. Appl., 1989,386,083(Chem. Abs., 1991, 115, 30129J). L. S. Meriwether, E. C. Colthup, G. W. Kennerly and R. N. Reusch, J. Org. Chem., 1961,26,5155. A. F. Donda, E. Cervone and M. A. Biancifiori, Recueil, 1962, 81, 585. 20 21 22 23 24 25 26 27 28 29 30 31 J. L. Koenig, Report AFWAL-TR-83-4064, 1983 (Chern. Ah., 1984,100,157487~). Sadtler Handbook of NMR Spectra, Sadtler Research Laboratories, 1978, (a) spectrum no. 8599M; (b) spectrum no. 5082M. K. P. C. Vollhardt, Angew, Chem., Int. Ed. Engl.. 1984,23, 539. H. Brunner and W. Pieronczyk, Bull. Soc. Chinz. Belg., 1977, 86, 725, and references therein. M. Dubeck, J. Am. Chem. Soc., 1960,82,502. M. Dubeck and A. H. Filbey, US Patent, 3256260 (Chem. Abs., 1966,65, 7307a). J. L. Davidson and D. W. A. Sharp, J. Chem. Soc., Dalton Trans., 1976,1123. V. 0.Reikhsfel'd, B. I. Lein and K. L. Makovetskii, Dokl. Akad. Nauk SSSR, 1970,190,125 (Proc.Acud. Sci.USSR, 1970,190,31). J. F. Tilney-Bassett, J. Chem. Soc., 1961, 577. A. Furlani, P. Bicev, M. V. Russo and M. Fiorentino, Gazz. Chim. Ital., 1977, 107, 373. G. Sartori, A. Furlani, P. Bicev, P. Carusi and M. V. Russo, Isr. J. Chem., 1976177, 15, 230. D. L. Trumbo and C. S. Marvel, J. Polym. Sci., Polym. Chem. Ed., 1987,25,1027. 18 R. C. Doss and P. W. Solomon, J. Org. Chem., 1964,29, 1567. 32 E. C. Colthup and L. S. Meriwether, J, Org. ChtJm., 1961,26,5169. 19 C. I. Simionescu, V. Percec and S. Dumitrescu, J. Polym. Sci., Polym. Chem. Ed., 1977, 15,2497. Paper 4/0034lA; Received 19rh Junuary,1994

ISSN:0959-9428    

DOI:10.1039/JM9940401167

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(8),1173-1180 Examination of the Structural Features necessary for Mesophase Formation with Aroylhydrazinato-nickel(i1) and -copper(ii) Complexes Mohammed N. Abser: Martin Bellwood," Christina M. Buckley," Michael C. Holmesb and Richard W. McCabe*a a Department of Chemistry, University of Central Lancashire, Preston, UK PR7 2HE Department of Physics and Astronomy, University of Central Lancashire, Preston, UK PRI 2HE N-Methylidene complexes and a series of N-alkylidene- and N-arylalkylidene-aroylhydrazinato-nickel(i1)and -copper(ii) complexes were synthesized in high yield and their mesomorphic nature studied. Only the N-methylidene coniplexes gave mesomorphic compounds as the larger N-alkylidene or N-aralkylidene groups probably prevented mesophase formation due to increased molecular broadening effects. The nickel(i1) complexes were found to be highly stable even in the isotropic phase and generally gave wide liquid-crystalline temperature ranges.This contrasted with the very narrow temperature ranges of the copper(ii) complexes, which rapidly decomposed in or just before attaining the isotropic phase. In a previous communication' the mesomorphic nature of some N-methylidene complexes was described. In order to explore further the formation of mesophases with these complexes, other N-methylidene complexes and a series of N-alkylidene- and N-arylalkylidene-aroylhydrazinato-nickel@) and -copper@) complexes were synthesized. Aroylhydrazones 1 and their parent hydrazines 2 form stable chelates with transition metals.2 The tuberculostatic activity of these compounds has been attributed to the forma- tion of stable chelates with transition metals present in the ell.^-^ Thus it seemed that such ligands might be used to form a new family of metal-containing liquid crystals, which, in contrast to many of the currently known metallome~ogens,~ would prove to be thermally stable.0 I1 R-C-NH-N=CH-R' 0 II R-C-NH-NHZ 1 2 N-Alkylidenearoylhydrazones 1 can coordinate to a divalent metal ion either via the enolic form (as in 3) or the ketonic form (as in 4 or 5).8-1' The square-planar complexes 3 and 4 would show the greatest promise as liquid crystals as the planar portion of such molecules would more easily align side by side than the non-planar octahedral complex 5.In the current study we present only the neutral compounds of type 3, although work has begun on ionic compounds 4. 12+ II CI 3 4 5 The tendency of the ligands 1 to react with nickel@) in the enolic form 6, to give complexes 3 (M =Ni), becomes greater as the conjugating ability of the R group in the hydrazine residue increases.12 Thus, aryl substituents favour the enolic tautomer of such ligands:I3 0 OH II I R-C-NH-N< R-C=N-N< keto 7 end 6 Furthermore, the coordinating ability of the counterion to the metal determines whether the octahedral or square-planar complex is formed.2 For instance, aroylhydrazones react with nickel(i1) acetate yielding the corresponding bis(aroy1h ydrazi- nato)nickel(u) complexes 3 (M =Ni), with the deprotonation of the secondary imino hydrogen; whereas with nrckel(I1) chloride it gives dichlorobis(aroylhydrazinato)nickd(Ir) 5 (M =Ni).The octahedral dichlorobis(aroy1hydrazone) nickel(i1) 5 (M =Ni) complexes, however, can undergo dehalo- pronation with alcoholic potassium hydroxide to give the square-planar neutral complexes. With these facts in mind several types of complexes 8-1 1, with differing arrangements of substituents (mode of molecular elongation), were synthe- sized. The n-dodecyloxy group was chosen as it should be sufficiently long to allow mesophases to form. The first complex targeted as a possible metalloniesogen was bis [N-( 4'-n-dodecyloxybenzylidene) benzoylhydra zinato] nickel(I1) 8 and was synthesized by following the reactions in Scheme 1.Reaction of benzamide with hydrazine hydrate, by thc litera- ture method,14 gave the benzoyl hydrazine 13 as a white solid. A 'Williamson ether' type reaction between p-hydrox! benzal- dehyde and 1-bromododecane in the presence of sodium hydroxide in ethanol gave the p-dodecyloxybenzaldeliyde 14 as a low-melting yellow solid together with the elimination product dodec- 1-ene. The alkene by-product was readily separ- ated by distillation under reduced pressure. The benzoy l hydra-zine 13 reacted with the aldehyde 14 in refluxing ethanol to give the benzoylhydrazone 15 as a white solid. Reaction of the hydrazone 15 with nickel@) acetate, again in refluxing zthanol, afforded the complex bis [N-(4'-n-dodecyloxybenzylidc~1e)ben-zoylhydrazinato] nickel@) 8 as an orange-yellow solid Note that although 8 can exist as one of three isclmers 8, 16, 17, 'H NMR spectroscopy shows only one methylene resonance at 6 7.18.This excludes the asymmetric structure 17 which should show two such resonances. 3D molecular modelling (Chem3D plus on the Apple Macintosh1 of the remaining symmetrical structures 8 and 17 shows that 8 would be more planar and sterically less hindered than 17, which suggests that the formation of the more conjugated isomer 8 would be preferred. On these grounds we propose an (E,E)-configuration for 8. 8 was examined under a hot-stage polarising microscope but unfortunately it was found to melt at 173-174 "Cwithout forming a mesophase.Since 8 was shown to be non-mesomorphic, an attempt was made to change the mode of molecular e1ong;ition. It was thought that the molecular lengthening along the axis of J. MATER. CHEM., 1994, VOL. 4 0 0 R = n -alkyl 10 11 12 0!-NH2 i"ref lux H-EGOH t C12HsBr 13 14 reflux1 EtoH 15 Scheme 1 Synthesis of 8 J. MATER. CHEM., 1994, VOL. 4 the 'benzoyl' benzene ring, as in 9, would result in a more linear molecule and might enhance the possibility of forming a mesophase. The complex, bis [N-benzylidene( 4'-n-dodecyloxy) benzoyl- hydrazinato] nickel(I1) 9, was synthesized following the route shown in Scheme 2. Ethyl p-hydroxybenzoate reacted under reflux in ethanol with 1-bromododecane in the presence of potassium hydroxide to give ethyl p-dodecyloxybenzoate 18 (R =C12H25), as a white low-melting crystalline solid, which on treatment with hydra~ine,'~ gave the p-dodecyloxy- benzoylhydrazine 19 (R =C12H25) as a white solid.Hydrazine 19 (R =C12H25) was then converted to the hydrazone 20 (R' = C12H25) by reaction with benzaldehyde in refluxing ethanol. Subsequent reaction of the hydrazone 20 (R' =C12H25) with alcoholic nickel@) acetate gave 9 as an orange-yellow solid. Again, unfortunately when observed under the hot-stage polarising microscope 9 showed a sharp transition from crystal to isotropic liquid at 161-162 "C without forming a mesophase. As it was evident from the melting behaviour of the hydrazinatonickel(I1) complexes 8 and 9 that the elongation along either 'end' of the molecule, i.e.via the benzoyl or benzylidene rings, does not confer the proper geometric requirements for the complex to be mesomorphic, it was decided to put a long hydrocarbon chain at both the benzoyl and benzylidene ends of the system on the assumption that the molecular elongation in both directions might introduce some mesomorphic properties (possibly discotic) into the system. With this in mind we synthesized the ligand 21 from aldehyde 14 and acylhydrazine 19 (R =C12H25), which on reac- tion with nickel(I1) acetate gave the orange crystalline complex, bis [(N-(n-dodecylox y) benzylidene) (n-dodecylox y) benzoylhy-drazinato] nickel(I1) 10.21 10 was found to melt at 77-78 "C, again without forming a mesophase. The non-mesomorphic character of this com-pound was also evidenced by differential scanning calorimetric (DSC) analysis, which showed a single transition at 77.77 "C (AH=51.5 kJ mol-', AS=147 J mol-' K-') corresponding to its transition to isotropic liquid. EtO-FOOH + RBr KOH zG1 1819 Scheme 2 Synthesis of 9 1175 From a thorough re-examination of the structure of the hydrazinatonickel(11) complexes described so far, it is apparent that the presence of a phenyl or a substituted phenyl ring in the azomethine (N-N=C) moiety, considerably broadens the molecular width. Moreover, owing to the proximitv to the central dihydrazinato ring, the benzylidene phenyl riiig is not coplanar with the central hydrazinatonickel ring.rhis broadening of the molecular width and the non-coplarity of the benzylidene ring is probably the underlying reason for non-mesomorphic behaviour of the complexes 8-10. I'hus it was realised that to impart the desired mesomorphic properties to the system, the substituent at the azomethine moiety should have the smallest possible size to minimisc the molecular broadening effect. A simple methylidene group was thought to be appropriate for this purpose. Accordingly the complex bis [N-methylidene-( 4'-n-dodecyloxy) benzoylhydraz- inato]nickel(~r)11 (R =C12H25) was synthesized by reaction of nickel(i1) acetate with N-methylidene( 4'-n-dodecyloxy) ben- zoylhydrazone 22 (R =C12H25).The latter was generated in situ by reaction of n-dodecyloxybenzoylhydrazine 19 (R =C12H25) with formaldehyde. h 22 11 (R =C12H25) was an orange-yellow microcrystalline solid, obtained by the usual work-up followed by re-crystallization from dichloromethane. A notable feature of the 'H NMR spectrum of this material is the unusually large coupling constant (J= 10.9Hz) shown by the two separate methylidene proton doublets at 6 7.05 and 6.47. The other features of the 'H NMR spectrum were as expected and are fully consistent with the structure 11 (R=C12H25)-On examination under the hot-stage microscope 11 iR= C12H25) showed a crystal to smectic C transition at 126.2"C which, on further heating, melted to the isotropic liquid at 164-165°C.On cooling the sample from the isotropic liquid, the smectic phase reappeared at 164 "C, but supercoolirig to 112-1 14 "C occurred before the solid crystalline phase reformed. After having established that the N-methylidenenickel(I1) complex 11 (R =C12H2,) does indeed show mesomorphic behaviour, it was of interest to study the effects of vari'ition of the alkyl chain length and the central metal atom to see what impact such changes had on the mesophase behaviour of these complexes. We synthesized seven homologues of 11 with different alkyl chain lengths (C4, c6, C8, Cl0, C14, CZ0 and C22). These complexes were prepared by a route similar to that employed for complex 11 (R =C12H25). The complexes 11 were obtained as crystalline orange solids and they all formed mesophases. Polarising microscop! and DSC experiments (Fig.1 and Table 1)were used to determine the phase change temperatures of the complexes 11, but the complex 11 (R=C,H,) was unstable and DSC data were not obtained. The complexes 11 (R =C4H9) and (R =C6H13) showed only nematic mesophases, whilst 11 (R =C,H,,) and (R =C1,H2,) showed both nematic and smectic C mesophases. The rernain- ing complexes showed only smectic C mesophases. The mesophases were identified by a combination of polarising microscopy and X-ray diffraction studies, both in our labora- tories and at the SRS facility at Daresbury. Polarising microscopy showed characteristic 'soft' schlieren textures for the nematic phases and a sharper more clearly defined schlieren texture with the smectic C mesophases.Typical textures given 1176 1802oiI 140-120-I 4 2 6 10 14 18 22 no. of carbons in alkyl chains Fig. 1 Transition temperatures of the bis [N-methylidene-(4'-n-alkyl-oxy) benzoylhydrazinato] nickel@) complexes, 11, observed by polaris- ing microscopy: 0,K+N; 0, K,+K2; 0, K-S,; A,K2-+S,; a,Sc+N; +, N+I; 0,Sc+I Table 1 DSC data for the bis [N-methylidene( 4'-n-alkyloxy) benzoyl- hydrazinatol-nickel(11) complexes 11 R phase change T/"C AH/kJmol-' AS1 J mol-' K-l 159.12 14.71 34.03 160.74 15.28 35.22 184.42 0.38 0.83 149.21 70.61 167.18 164.54 0.31 0.72 174.60 1.65 3.70 141.41 107.33 258.91 166.79 0.93 2.12 182.34 1.27 2.78 135.22 81.64 199.92 123.48 21.22 53.50 125.47 54.04 135.57 156.71 3.30 7.67 125.32 56.61 142.07 135.32 69.85 171.00 154.80 8.03 18.77 132.40 158.00 389.58 142.33 12.14 29.21 101.20 -25.73 -68.74 123.29 127.48 321.56 130.33 6.17 15.29 106.42 -7.87 -20.72 a Transitions too close to separate.Second heating cycle. 'Cooling cycle. under the polarising microscope by the nematic and smectic phases of these compounds are shown in Plates 1 and 2. X-Ray diffraction showed the classical diffuse arcs either side of the beam for the nematic mesophases, whilst the smectic C phases showed diffuse arcs from intralamellar scattering and Bragg peaks from interlamellar (do) scattering.Selected interlayer spacings, c, for the smectic C phases of these complexes are given in Table 2. All of the complexes showed extensive supercooling, the C,, Clo and C1,complexes showed a crystal to less ordered crystal transition before the mesophase was obtained, whilst J. MATER. CHEM., 1994, VOL. 4 the Czo and C,, complexes also showed a disordered to ordered crystal transition on supercooling. When these com- plexes were cooled the less ordered crystalline phase was obtained and in the case of 11 (R=C,,H,,) only, the K2-+S, transition decreased (from 141 to 135 "C) in subsequent heat- ing cycles. The more ordered crystalline phase K, could be recovered by recrystallising the less ordered material IS2.The ordered crystalline material is probably a kinetically formed crystalline form, whilst the other is the thermodynamically more stable form.It had become evident from the melting behaviour of the benzoylhydrazinatonickel(11) complexes 8-1 0 that a substitu-ent at the azomethine moiety leads to excessive broadening of the system which eliminates the mesomorphic properties of the complexes. However, it was felt that it would be worthwhile examining a complex with a methyl substituent on the azomethine moiety, which, although it is more gluobu- lar than a phenyl ring, might be tolerated by the system without preventing mesophase formation. Thus we obtained the orange crystalline complex bis [N-ethylidene( 4'-n-dode- cyloxy) benzoylhydrazinato] nickel(r1) 12 by a similar synthetic route to that used for complexes 11, i.e.by replacing the original formaldehyde with acetaldehyde. Once again 12 was found to be formed exclusively as only one of the three possible isomers, as evidenced by its 'H NMR spectrum showing only one doublet for the ethylidene CH, protons at 6 2.28 (J= 5.6 Hz). Although the methine proton (=CgCH,) should resonate as a quartet in the 'aromatic region' (by analogy with the benzylidene deriva- tives), the methine proton signal in the complex accidentally coincides with one of the doublets for the phenyl ring protons at 6 6.7-6.8 (total integration of 6 protons). Thus the splitting pattern for the methine proton could not be seen. The rest of the 'H NMR spectrum was consistent with the expected structure.On the basis of these 'H NMR data together with 3D modelling studies as before, we again assigned the (E,E)-configuration to 12. 12 was found to melt at 153-154.5 "C, again without forming a mesophase. Several copper analogues 23 of the mesomorphic nickel(r1) complexes 11 were synthesized in order to determine the impact of the change in central metal atom on the mesophase behaviour of the system. The copper complexes 23 were obtained as brown solids by replacing nickel(r1) acetate by copper(I1) acetate in the normal synthetic route. As expected, these complexes are paramagnetic and because of this para- magnetism the 'H NMR' signals of these complexes are so distorted that they provide little information regarding the structural characterisation of the complexes.In fact, the 'H NMR spectrum of these complexes shows no signal at all around the usual aromatic region as the protons for this region are close to the paramagnetic central metal atom; however, in the upfield region there are resonance signals characteristic of a long alkoxy hydrocarbon chain, although again the signals were too broad to see the splitting pattern of these signals. 23 Observation of the CI2complex 23 (R=C12H25) under the polarising microscope showed the characteristic changes in J. MATER. CHEM., 1994. VOL. 4 Plate 1 Schlieren texture of the nematic phase of 11 (R=OC,H,,) (x5 magnification) Plate 2 Schlieren texture of the S, phase of 11 (R=OC,H,), optical texture which accompanied mesophase formation at 139-140 C.The type of mesophase formed has not yet been identified, however, as unfortunately, the complex proved to be too unstable to perform either XRD or DSC experiments on. On the hot-stage polarising microscope the complex was seen to decompose to a glassy product at ca. 147°C before entering the isotropic phase. The C,, analogue 23 (R= 138 C, on cooling from the isotropic phase (x5 magnification) C,,H,,) showed parallel behaviour, beginning at the eievated temperature range of 150-152'C. These mesogenic copper(r1) complexes have similarities in shape to the copper(rr) /J-diketonate complexes, described by Ohta et al.,16.17which showed multiple melting behaviour.Modifications of the secondary side-chain, similar to those carried out in our work, of the basic copper(1r) P-dikctonate Table 2 Selected interlayer spacing data for the smectic C phases of the bis[N-methylidene (4'-n-alkyloxy) benzoylhydrazinato] nickel (n) complexes 11 R interlayer spacing, c/A T/"C 34.0 152 39.5 144 38.6 157 37.9 163 40.0 145 40.5 150 37.0 154 44.0 140 46.2 132 51.4 122 49.4 126 49.2 128 structure have produced several series of liquid-crystalline materials. Several of these complexes give liquid-crystalline phases; i.e. discotic, nematic and in some cases smectic A and smectic C mesophases have been Many of these complexes apparently oxidise when they are heated in air, thus the thermal instability of our copper(11) complexes is not too unexpected.l9 These promising compounds need careful re-examination. In conclusion, we have found that nickel@) and copper(I1) complexes with N-methylidenearoylhydrazinato ligands are mesogens, whilst other alkylidene-and aralkylidene-substituted ligands failed to form mesophases. The nickel(r1) complexes proved to be thermally stable [except for the high-melting complex 11 (R =C,H,)] and to have fairly wide liquid-crystalline ranges, whereas the copper(11) complexes decomposed soon after entering the mesophase. Experimental General All reagents were used as purchased. Commercially obtained ethanol and methanol were used without further purification; all other solvents were dried with an appropriate drying agent and distilled under nitrogen.The 'H NMR spectra were obtained on Hitachi R1200 (60 MHz) and Bruker WM250 (250 MHz) spectrometers. The FTIR spectra were recorded using a Mattson Polaris Icon Spectrometer and the GC-MS were obtained on a Perkin-Elmer 8500 Gas Chromatograph with an ITD Ion Trap Detector. Microanalyses were carried out as a service by the University of Manchester. Melting points were found using a Gallenkamp melting-point appar- atus or a Vickers microscope fitted with crossed polarisers and a Linkam PR600 hot stage and are uncorrected. X-Ray diffraction studies were carried out using a heated pinhole camera connected to a Hiltonbrooks X-ray generator and a Digital Imaging Systems DIS 3000 area detector.Thin-layer chromatography (TLC) was carried out using Kieselgel 60 F254 (from Merck) of thickness 0.20 mm (analytical). For preparative purposes spinning plates of Kieselgel 60 G (Chromatotron) of thickness 2 mm were used. Benzoylhydrazine 13 The benzoylhydrazine 13 was synthesized by the general literature method.I4 A mixture of benzamide (12.1 g, 0.1 mol) and hydrazine hydrate (5 g, 0.1 mol) was heated under reflux in water (40 cm3) for 3 days. When the mixture was cooled to room temperature a yellow-white solid separated out and was filtered off under suction, washed with cold ethanol (20 cm3) J. MATER. CHEM., 1994, VOL. and ether (20 cm3) and finally recrystallised from boilini, ethanol to give white crystals of the pure 13 (log, 74%) mp 112°C (lit.', 112.5"C); v,,, (CH,Cl,)/cm-': 3440, 333(1 (N-H), 3000-30230 (aromatic C-H), 1670 (amide I), 1624 (amide 11), 1578 and 1500 (aromatic C=C), 1470 (s), 1290 (m) 1100 (w), 940 (m), 660 (w); 6, (CDCl,, 250 MHz): 8.05 (1 H br s, NH-NH,), 7.72-7.75 (2 H, m, C6H5), 7.25-7.52(3 H, m C,H,), 3.66 (2 H, br s, NHNH,).-4Dodecyloxybenzaldehyde 14 Sodium hydroxide (6 g, 150 mmol) was added in portions to a refluxing ethanolic solution (150 cm3) of 4-hydroxy-benzaldehyde (12 g, 98 mmol) and l-bromododecane (24 g.96.4 mmol). After a further 10 h under reflux the mixture was cooled to room temperature and neutralised to litmus with dilute hydrochloric acid, extracted with ether (5 x 30 cm3). dried over Na2S0, and the solvent removed in uucuo to give a yellow oil. Distillation under reduced pressure gave a colourless liquid at 118-120°C at ca.4 mmHg, which proved to be dodec-1-ene. The residual oil was dissolved in petroleum ether (bp 60-80 "C) and left in the refrigerator overnight when a yellow solid separated out. This solid (12 g, 42%) was filtered off under suction, using cool conditions, and dried under high vacuum. The compound melted below ca. 3OCC, 6H (CDCl,, 250 MHz): 9.86 (1 H,s, CHO), 7.82 (2 H,d, J 8.25, C6H4) 6.99 (2 H, d, J 8.25, C6H4)74.03 (2 H, d, J, 6.5, OCH,CH,), 1.77 (2 H, m, OCH,CH,CH,), 1.2-1.4 [lS H, m. OCH2CH2(C~,),CH,], 0.88 (3 H, t, J 6.5, CF,). N-(4-n-Dodecyloxy) benzylidene-N-benzoylhydrazine 15 A suspension of 13 (0.68 g, 5mmol) and 4-n-dodecyloxybenzal- dehyde (1.45 g, 5 mmol) in ethanol (25 cm3) was heated under reflux for ca.1 h. The reaction mixture was cooled to room temperature and the yellowish solid product was collected by filtration under suction. Recrystallisation from chloroform gave 15 as a white crystalline solid (1.6 g, 78%), mp 143-145 "C; vmax (CH,Cl,)/cm-': 3350, 3300 (N-H), 3020 (aromatic C-H), 2920,2860 (aliphatic C-H), 1680 (amide I), 1604 (amide 11), 15746, 1505 (aromatic C-C). bis [4-n-Dodecyloxybenzylidenebenzoylhydrazinato]nickel(II ) 8 An ethanolic solution of nickel@) acetate (0.12 g, 0.84 mmol) was added to a refluxing solution of 15 (0.4g, 1.0mmol) in ethanol (25 cm3) and heating continued for a further 30 min. After cooling the mixture to room temperature the orange- yellow solid was filtered off, washed with ethanol (50 cm3), water (100 cm3) and finally with hot methanol until the filtrate was clear.The solid was dried under suction and recrystallised from chloroform to give 8 as an orange-yellow solid from a deep orange-red solution (0.30 g, 70°h), mp 173-174 "C. (Found: C, 71.2; H, 8.4; N, 6.3%. C,,H,,,N4O4Ni requires: C, 71.5; H, 8.1; N, 6.4%), 6H (CDCl,, 250 MHz): 8.33 (4 H, d, J 8.9, C&4), 7.98 (4H, m, C6H5), 7.35, 7.49 (6 H, m, C6Hs), 7.19 (2 H, s,N=CH), 6.98 (4H, d,J 8.9, C6H4), 4.04 (4 H, t, J 6.5, OCH,), 1.7-1.8 (4 H, m, OCH,CH,CH,), 1.15-1.6 [36 H, m, ~CH,CH,(CH,),CH,],, 0.8876 H, t, J 6.5 Hz, CH,); dC (CDCl,, 250 MHz): 175.5, 161.8, 152.8, 135.0, 130.7, 130.6, 128.6, 128.0, 122.8, 114.3, 68.2, 31.2, 29.63, 29.58, 29.4, 29.3, 29.1, 26.0, 22.7, 14.1.Ethyl 4-n-Alkyloxybenzoates 18 Potassium hydroxide (10 g, 0.18 mol) was added in portions to a refluxing ethanolic solution (200cm3) of ethyl 4-hydroxybenzoate (16.6 g, 0.1 mol) and the l-bromoalkane (0.1 mol). After heating the mixture under reflux for a further J. MATER. CHEM., 1994, VOL. 4 150 min the reaction mixture was cooled to room temperature neutralised (litmus) with dilute hydrochloric acid, extracted with ether (4 x 75 cm3), dried (Na,SO,) and evaporated in vacuo. The residual mass on treatment with petroleum ether (60-80 "C) (50 cm3) gave a small amount of white solid which was filtered off.The filtrate was evaporated in U~CUOand crystallised from petroleum ether (60-80 "C)-ether (ca. 10%) to give the title compounds as white crystalline solids which were filtered offunder cold conditions as many of them melted near room temperature. The following ethyl 4-n-alkyloxybenzoates 18 were prepared by the above method. Ethyl 4-n-butyloxybenzoate 18 (R =C4H9) (15.76 g, 71 %); vmaX (Nujol)/cm-': 2959, 2932, 2872 (aliphatic C-H), 1722 (C=O), 1611, 1575, 1500 (aromatic C=C), 1454 (s), 1488 (w), 1367 (s), 1308 (w), 1275 (s), 1178 (s), 1107 (s), 1023 (s), 845 (s), 772 (s), 703 (s); 6, (CDCl,, 250 MHz): 7.96 (2 H, d, J 9, C,H4), 6.86 (2 H,d,J 9, C6H4), 4.31 (2 H,q,J 7.2, OCH,CH,), 3.95 (2 H, t, J 6.6, OCH,CH,), 1.74 (2 H, m, OCH,CB,CH,), 1.37 [5 H, m, O(CH,),(CH,)CH, and OCH,CH,], 0.95 [3 H, t, J 6.5, 0(CH2 ),Cg 3 1 Ethyl 4-n-Hexyloxybenzoate 18 (R =C6H1,) (20 g, 80%).Ethyl 4-n-Octyloxybenzoate 18 (R =C,H,,) (24.97 g, 69%). Ethyl 4-n-Decyloxybenzoate 18 (R =C,,H,,) as low-melting white solid (22 g, 72%). Ethyl 4-n-Dodecyloxybenzoate 18 (R =C12H25) (25 g, 75%). Ethyl 4-n-Tetradecyloxybenzoate18 (R =C14H29) (24.25 g, 67%); mp 35.4-36.3 "C. Ethyl 4-n-Eicosyloxybenzoate 18 (R =C20H41) (18.69 g, 42%); mp 75.4-76.2 "C. Ethyl 4-n-Docosyloxybenzoate 18 (R =C22H45) (18.4 g, 39%); mp 60.6-41 "C. 4-n-Alkyloxybenzoylhydrazines 19 The hydrazines 19 were synthesized by following a general literature method.', A mixture of 18 (3 mmol) and hydrazine hydrate (1g, 20 mmol) was heated under reflux in ethanol (20 cm3) for 24 h.On removal of the solvent in uacuo, the residual solid was washed with water and recrystallised from ethanol (short chains) or chloroform (longer chains) to give the compounds 19 as white solids. The following 4-n-alkyloxybenzoylhydrazines19 were pre- pared by the above method. 4-n-Butyloxybenzoylhydrazine19 (R =C4H9) (0.47 g, 75%), mp 91.8 "C; vmax (Nujol)/cm-': 2948, 2919, 2855, (aliphatic C-H), 1720 (C=O), 1600, 1575, 1500 (aromatic C=C), 1451 (s). 1377 (s), 1316 (w), 1277 (s), 1255 (s), 1159 (s), 1018 (s), 845 (s), 721 (s); hH (CDCl,, 250 MHz): 8.06 (2 H, d, J 8.8, C,H,), 7.3 (1H, b, overlapped by solvent peak CHCl,, NHNH,), 6.95 (2 H, d, J 8.8, C6H4), 4.05 (2 H, t, J 6.5, OCH,CH,), 3.05-3.7 (2 H, b, NHNH,), 1.82 (2H, m, OCH,CH ,CH,), 1.28, [2 H, m, OCH,CH,(CEJ,)CH,), 0.90 (3 H, t, J6.25, CH,].4-n-Hexyloxybenzoylhydrazine 19 (R =C6H13) (0.53 g, 75%); mp 97-98 "C. 4-n-Octyloxybenzoylhydrazine 19 (R =CsH17) (0.6 g, 74%), mp 73.4"C. 4'-n-Decyloxybenzoylhydrazine 19 (R =C10H21) (0.76 g, 74%); mp 93-94°C. 4-n-Dodecyloxybenzoylhydrazine 19 (R =C,,H,,) (0.8 g, 84%); mp 92-94°C. 4-n-Tetradecyloxybenzoylhydrazine19 (R =C14H29) (0.64 g, 72%); mp 854°C. 4-n-Eicosyloxybenzoylhydrazine 19 (R =C2,H,,) (0.46 g, 68%); mp 118 "C. (Found: C, 75.7; H, 10.9; N, 6.5%; C&,8N@2 requires: C, 74.95; H, 11.18; N, 6.47%). 1179 4-n-Docosyloxybenzoylhydrazine 19 (R =C22H45) (0.5 g, 72%); mp 116.4 "C.N-Benzylidene-N-( 4-n-dodecyloxy) benzoylhydrazine 20 This was synthesized using a similar method to that used for N-(4'-n-dodecyloxy)benzylidenebenzoylhydrazine 15. Reaction of 19 (R= C12H25) (0.64 g, 2 mmol) with benzal- dehyde (0.21 g, 2 mmol) in refluxing ethanol (20 cm3) gave 20 as a white solid on recrystallisation from chloroform; (0.7 g, 86%); mp 136-137 "C; v,,, (CH,Cl,)/cm-l: 3355,3300 (NH), 2920, 2845 (aliphatic C-H), 1676 (amide I), 1604, 1572, 1500 (aromatic C=C). bis [N-Benzylidene (4-n-dodecylox y)benzoylhydrazinatril-nickel(r1) 9 This complex was synthesized using a similar method to that used for 8. Treatment of 20 (0.4 g, 0.98 mmol) with nickel(r1) acetate (0.3 g, 0.8 mmol) in ethanol (25 cm3), under reflux, and with the usual work-up followed by crystallisation from dichloro- methane, gave the orange-yellow complex 9 (0.3 g, 72%); mp 161-162 "C.(Found: C, 71.2; H, 8.4; N, 6.2%. C52H70Y404Ni requires: C, 71.2; H, 8.4; N, 6.4%), v,,, (CH2C1,)/cm-2920, 2855 (aliphatic C-H), 1605, 1584, 1500 (aromatic C=C); BH (CDCI,, 250 MHz): 8.28 (4 H, m, C,H5), 7,88 (4 H, d, J 8.8, C6H4), 7.44 (6 H, m, C6H5), 7.16 (2H, s, N=CH), 6.84 (4H,d, J 8.8, C6H4), 3.96 (4H, t, J 6.5, OC€f,C%), 1.79 (4H, m, OCH,CH,CH,), 1.1-1.5 [36H, m, OCH,CH,(CH,),CH,], 0.88(6 H, t, J 6.5, CH,); 6, (CDCl,, 250MHz): 175.9, 161.6, 152.2, 132.6, 131.2, 13T1, 130.4, 128.4, 122.5, 113.9, 68.1, 31.9, 29.7, 29.6, 29.41, 29.35, 29 2, 26.0, 22.7, 14.1. N-(4-n-Dodec ylox y)benzylidene-N-( 4-n-dodecylox y)-benzoylhydrazine 21 A mixture of 19 (R =C,,H25) (0.64 g, 2 mmol) and 14 (0.5 g, 2 mmol) was heated under reflux in ethanol (20 cm3) for 1 h.On cooling the reaction mixture the solid product was separ-ated by filtration and recrystallised from chloroform to give the hydrazine 21 as a yellow-white solid (1.0 g, 92%); mp 140-141.5 "C; v,,,(CH,Cl,)/cm-l: 3358, 3308 (NH ), 2922, 2548 (aliphatic C-H), 1675 (amide), 1604, 1574, 1500 (aro- matic C=C). bis [N-(4-n-Dodecyloxy) benzy1idene)-N-( 4-n-dodecyloxy- benzoyl) hydrazinato] nickel(r1) 10 A hot ethanolic solution of nickel@) acetate (0.1 g, 0.4 mmol) was added to a refluxing ethanolic solution (25 cm3) of 16 (0.4 g, 0.74 mmol). After heating the mixture under reflux for a further hour, the reaction mixture was cooled to room temperature when a deep orange-red solid separated.The solid was filtered off under suction, washed with ethanol, water and finally with hot methanol. Recrystallisation from toluene gave the pure complex 10 as orange-red crystals (0.3 g, 72%); mp 77.7 "C (A,=41.52 J g-l). (Found: C, 73.7; H, 9.9; N, 4.4%. C76H118N406Ni requires: c, 73.5; H, 9.6; N, 4.5%); v,,, (KBr)/cm-': 2920, 2840 (aliphatic C-H), 1595, 1580, (aromatic C=C); 8, (CDCl,, 250 MHz): 8.3 (4H,d, J 8.8, C6H4), 7.89 (4 H, d, J 8.8, C6H,), 7.10 (2H, s, CEJ), 6.95 (4 H,d, J 8.8, C6H4), 6.85 (4 H, d, J 8.8, C,H,), 3.9-4.0 (8 H, m, OCH,CH,), 1.80 (8 H, m, OCH,CEJ,CH,), 1.1-1.56 [72 H, 6OCH,CH,(CH,),CH,], 0.88 (12 H, t, J 6.5); 6, (CDCl,, 250 MHz): 175.1, la.4, 161.3, J.MATER. CHEM., 1994, VOL. 4 151.7, 134.8, 130.2, 124.3, 123.0, 114.3, 113.9, 68.2, 68.1, 31.9, 29.7, 29.6, 29.4, 29.3, 29.2, 29.16, 29.0, 22.7, 14.1. bis [N-Methylidene (4-n-alkyloxy) benzoylhydrazinato] -nickel(11) complexes 11 Formaldehyde (0.094 g, 3.13 mmol; 0.27 g, 35% w/w sol.) was added to a refluxing ethanolic solution (25 cm3) of 18 (3.13 mmol) and heating was continued for ca. 20 min to complete formation of 22. Nickel(I1) acetate (0.4 g, 1.6 mmol) was then added to the reaction mixture and reflux was continued for another 20 min. The resulting orange-yellow solid was collected by filtration and washed thoroughly with ethanol, water and finally with hot methanol. Recrystallisation from hot dichloromethane gave 11 as crystalline orange- yellow solids.The following nickel(I1) complexes 11 were prepared by the above general method: bis [N-Methylidene( 4’-n-butyloxybenzoyl) hydrazinato] nickel@) 11 (R=C4Hg) (0.53 g, 68%); v,,, (Nujol)/cm-l: 3315, 3275 (N-H) 2952, 2922, 2853, (aliphatic C-H), 1648 (C=O), 1619 (amide II), 1595,1571,1507 (aromatic C=C); dH(CDCl,, 250 MHz): 7.8 (4 H, d, J 8.8, C6H4), 7.085 (2 H, d, J 10.9 one of N=CH,), 6.85 (4 H, d, J 8.8, C6H4), 6.515 (2 H, d, J 10.9, one of N=CH2), 3.98 (4 H, t, J 6.6, OCH,CH,), 1.77 [4 H, m, OCH,(CH,)CH,], 1.31 [4 H, m, O(CH,),(CH,)CH,), 0.9 (6 H, t, J3.3, CH,). bis [N-Meth ylid&e( 4’-n-hexyloxybenzoyl) hydrazinato] nickel@) 11 (R=C&13) (0.665 g, 73%); (Found: C, 60.5; H, 7.0; N, 10.1%. C28H38N404Ni Requires: C, 60.8; H, 6.9; N, 10.1%).bis [N-Methylidene( 4’-n-octyloxybenzoyl) hydrazinato] nickel@) (14, R=C8H17) (0.58 g, 62%); Found: C, 63.1; H, 7.6, N, 9.4%. C3,H4,N4O4Ni Requires: C, 63.07; H, 7.61; N, 9.19%). bis [N-Methylidene( 4-n-decyloxybenzoyl )hydrazinato] nickel@) 11 (R=C10H21)(0.85 g, 82%); (Found: C, 63.9; H, 8.2%, N, 8.4%. C36Hs4N404Ni Requires: C, 65.0; H, 8.2; N, 8.4%). bis [N -Methylidene (4’ -n -dodecyloxy) benzoylhydrazinatol- nickel(r1)11 (R =C12H25) (0.9 g, 80%); (Found: C, 65.6; H, 8.2; N, 7.7%. C40H62N404Ni Requires: C, 66.6; H, 8.7; N, 7.8%). bis [N-Methylidene (4’-n- tetradecyloxybenzoyl) hydrazinatol- nickel(r1) 11 (R =C14H29 ) (0.86 g, 69%). bis [N -Methylidene (4’ -n -eicosyloxybenzoyl) hydrazinatol- nickel(I1) 11 (R=C,,H,,) (1.08 g, 73%).bis [N -Methylidene (4’ -n -docosyloxybenzoyl) hydrazinatol- nickel(1r) 11 (R=C,,H,,) (1.07 g, 69%). bis [N-Ethylidene (4-n-dodec yloxy) benzoylhydrazinatol-nickel(11) 12 The complex 12 was synthesized by a similar method to that used for the complexes 11. Treatment of nickel(I1) acetate (0.39 g, 1.37 mmol) with a refluxing ethanolic solution (25 cm3) of 4-n-dodecyloxyben- zoylhydrazine 18 (R =C12H2s)(1g, 3.13 mmol) and acetalde- hyde (0.14 g, 3.13 mmol), followed by the usual work-up, gave an orange-yellow solid. It was recrystallised from hot dichloromethane to give the pure complex 12 as an orange- yellow microcrystalline solid (1.0 g, 86%); mp 154-154.5 “C (Found: C, 66.9; H, 8.6; N, 7.6%.C4,Hs6N4o4Ni Requires: C, 67.3; H, 8.9; N, 7.5%); dH (CDCl,, 250 MHz) 7.8 (4 H, d, J 8.3, C6H4), 6.7-6.8 (6 H,m, C6H4 and =CHCH,), 3.95 (4H,t,J 6.5, OCH,CH,), 2.28 (6 H,d,J 5.6,-=CHCH3), 1.77 (4 H, m, OCH,CH,CH,), 1.1-1.5 [36H, OCH,CH,(CH2),CH3], 0.87(6 H, t, J 6.0, CH,). bis [N-Methylidene (4-n-alkyloxy) benzoylhydrazinatol- copper(11) complexes 23 The copper(I1) complexes 23 were synthesized by a method similar to that used for the nickel(1r) complexes 11. Copper(I1) acetate (0.31 g, 1.55 mmol) was treated with a refluxing ethanolic solution of the 4-n-alklyloxybenzoylhydra-zine 19 (3.13 mmol) and formaldehyde (0.1 g, 3.3 mmol; 0.28 g of 35% w/w solution). The bro Nn-yellow solid was filtered off and washed thoroughly with water, hot ethanol and dried under suction to give the copper complex 23 as a brown solid.The following copper(I1) complexes 23 were prepared by the above general method. bis [N-Methylidem( 4-n-decyloxy )benzoylh ydrazinato] copper (11) 23 (R=C10H21)(0.83 g, 79%); mp K+L/C 150-152‘C (dec. ca. 160°C) (Found: C, 63.8; H, 8.1; N, 8.4%. C36H54N404C~ Requires: C, 64.5; H, 8.1; N, 8.4%); vmaX (KBr)/crn-l: 2915, 2844 (aliphatic CH), 1600 (hydrazinato ring C=N), 1585 (aryl C=C), 1495 (s), 1468 (m), 1412 (s), 1370 (s), 1308 (m), 1245 (s), 1212 (m), 1168 (s), 1105 (w), 1050 (w), 1025 (m), 970 (m), 960 (m), 850 (m), 820 (m), 764 (m), 720 (w), 690 (m), 664 (m). bis [N -Methylidene (4’-n -dodecyloxy) benzoylhydrazinatol- copper(I1) 23 (R=C12H25) (0.8 g, 71%); mp K-+L/C 139-140 “C (dec.ca. 147 “C); vmax (KBr)/cm-’: 2910, 2840 (aliphatic CH), 1600 (hydrazinato ring C =N), 1585 (aryl C=C), 1495 (s), 1465 (m), 1412 (s), 1370 (s), 1305 (m), 1242 (s), 1215 (m), 1172 (s), 1105 (w), 1020 (m), 1000 (w), 978 (w), 910 (m), 850 (m), 830 (w), 760 (m), 728 (w), 690 (w), 660 (m). We thank the British Technology Group for financial support, the Overseas Student Sponsorship Scheme for a studentship for M.N.A., Dr. Peter Styring at the University of Hull for carrying out some of the DSC measurements and Dr. Barry Hunt, Department of Physics and Materials, University of Lancaster for allowing us access to their DSC facilities. References 1 M. N. Abser, M.Bellwood, M. C. Holmes and R. W. McCabe. J. Chem. Soc., Chem. Commun., 1993,1062. 2 L. El Sayed and M. F. Iskander, J. Znorg. Nucl. Chem., 1971, 33,435. 3 Ng. Ph. Buu-Hoi, Ng. D. Xuong, Ng. H. Ham. F. Binon and R. Roger, J. Chem. Soc., 1953,1358. 4 T. S. Ma and T. M. Tien, Antibiotics Chemothrrapy, 1953,3,491. 5 Q. Albert, Nature (London), 1953,9, 370. 6 J. M. Price, R. R. Brown and F. C. Larson, J. Clinic.Invest., 1957, XXXVI, 1600. 7 D. W. Bruce, Inorganic Materials, eds. I>. W. Bruce and D. O’Hare, Wiley, Chichester, 1992. 8 J. M. Price, Federation Proc., 1961, 20, 223. 9 L. Sacconi, J. Am. Chem. Soc., 1952,74,4503. 10 H. Ohta, Bull. Chem. SOC.Jpn, 1958,31, 1056; 1960,33,202. 11 K. Nagano and H. Kinoshita, Chem. Pharm. Bull. Tokyo, 1964, 12, 1198. 12 L. Sacconi, J. Am. Chem. Soc., 1954,76,3400. 13 R. A. Morton, A. Hassan and T. C. Callofiay, J. Chem. Soc., 1934,883. 14 G. Struse, J. Prak. Chem., 1894,50, 295; 1895,52, 170. 15 A. I. Vogel, Practical Organic Chemistry, Longmans, 4th edn., 1978, p. 1125. 16 K. Ohta, M. Yokoyama, S. Kusabayashi and H. Mikawa, J. Chem. SOC., Chem. Commun., 1980,392. 17 K. Ohta, J. J. Guang, M. Yokoyama, S. Kusabayashi and H. Mikawa, Mol. Cryst. Liq.Cryst., 1981,66, 283. 18 Reviewed by: D. W. Bruce, in Inorganic Materials, ed. D. W. Bruce and D. O’Hare, Wiley, Chichester, 1992. 19 N. J. Thompson, J. W. Goodby and K. J. Toqne, Mol. Cryst. Liq. Cryst., 1992, 213, 187. Paper 3/07230D; Received 7th December 1993

ISSN:0959-9428    

DOI:10.1039/JM9940401173

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(8), 1181-1187 Gelation of Silicone Fluids using Cholesteryl Esters as Gelators Valerie J. Bujanowski, Dimitris E. Katsoulis* and Maris J. Ziemelis Materials Development Department, Dow Corning Corporation, Midland, Ml48686-0994, USA A variety of silicone fluids were found to gel using low concentrations (<2 wt.%) of cholesteryl anthraquinone-2- carboxylate (CAQ) and cholestanyl anthraquinone-2-carboxylate(CHAQ). These compounds are known to be effective gelators for a variety of organic fluids. The gelation process involved the use of a co-solvent to incorporate the CAQ and CHAQ into the silicone fluid, followed by its removal via a thermal treatment. Semi-clear to clear irreversible gels were formed in this way and optical and scanning electron microscopy revealed that their microscopic features are similar to those reported for the organic fluids.They form intertwined microscopic fibres which create a three- dimensional network that effectively immobilizes the silicone fluid. The silicone gels were found to be more stable at high temperatures than the organic gels. This is attributed to the much lower solubility of the gelator in silicone fluids at all temperatures. A number of other simple cholesteric compounds were also investigated as gelators of silicones. From those, cholesteryl phenylacetate was found to form a macrocrystalline network and to entrap the silicone fluid in a fashion analogous to CAQ. Owing to their large macrofibres, opaque paste-like gels were obtained. Studies on gelation phenomena have primarily involved organic fluids.'-16 For some time now we have been interested in the gelation of silicone fluids. We report here some prelimi- nary results using cholesteryl esters as gelators. Weiss and co-workers' have prepared several such compounds which are composed of polycyclic aromatic and steroidal groups linked together with short ester chains (ALS) and they have shown that these molecules are effective as thermally reversible gelators of organic fluids.Their optical and electron microscopy studies indicated that the gels are composed of a gelator network of domains of fibrous bundles that immobilize the fluid component. We carried out our gelation studies using cholesteryl anthraquinone-2-carboxylate (CAQ) as the primary model gelator.The results showed that the CAQ-silicone gels were more stable than the organic gels even at high temperatures. Also a co-solvent was needed in order to incorporate the gelator into the silicone fluids. These differences are attributed to the fact that the CAQ gelator is less soluble in most silicones than in the organic solvents. Once its fibrous network is formed, it is more difficult to break it down. A number of other cholesteryl esters were also screened and they are summarized in Table 1. Results and Discussion Gelation using Cholesteryl Anthraquinone-2-carboxylate Since CAQ is not soluble in silicone fluids a volatile organic co-solvent was used to solubilize it in silicones.We found that chloroform was a very effective co-solvent, because it is a good solvent for CAQ and with most silicones, and can be removed easily with gentle heating. Occasionally toluene was also used. As described in the Experimental section, organosil- icone gels were formed when a solution of CAQ in CHC13 and silicone fluid was heated on a hot-plate to evaporate the co-solvent and then cooled to ambient temperature. Table 2 lists the silicone fluids that were successfully gelled with CAQ. The two silicone amine copolymers and the poly(methy1- phenylsiloxane) with the lowest phenyl content (Dow Corning 510 Fluid) formed gels at elevated temperatures (while still on the hot-plate). Many fluids gelled at above ambient temperatures, most as soon as the solvent had been removed.The poly(methylphenylsi1oxane) (Dow Corning 710 Fluid) and the silicone glycol copolymer gelled at ambient tempera- ture. Presumably these fluids are better solvents for CAQ than the other siloxanes in Table 2. The organosilicone gels formed were between nearly transparent and opaque, depending upon the concentration of the gelator and the type of fluid. For example, a nearly transparent gel was produced by the incorporation of 0.5 wt.% CAQ in decamethylcyclopen- tasiloxane; on the other hand, the silicone glycol copolymer VII in Table 2 formed firm opaque (almost waxy) gels. At levels below 0.2 wt.% CAQ partial gelation occurred. For some organic silicone copolymers, such as poly( decyl- methylsiloxane), gelation did not occur (at ambient tempera- ture) when the CAQ concentration dropped below 0.5 wt.%. This was probably due to the high organic content of the siloxane (Table2) that made this fluid more compatible with CAQ.In some cases the gels that formed on the hot-platrb were not very uniform. This was due to chloroform evaporation at the surface, which allowed gel formation to start at the surface before all of the chloroform was removed. The remdining chloroform boiled underneath the thin layer of gel, bubbling up through the gel as it evaporated. The gels which formed at lower temperatures were more uniform because most of the chloroform was removed before the start of gel formation. Heating was necessary for the formation of the gels.Attempts to cause gelation of silicone fluids (i.e. PDMS 350 cSt) by omitting the heating step and allowing the chloroform to evaporate at ambient conditions or under reduced pressure were unsuccessful, resulting in precipitation of the CAQ gelator. The gels were not thermally reversible. Upon heating they collapsed to a cloudy white mixture, which changed to a clear liquid (silicone fluid) containing suspended crystals of CAQ. The gels could be reformed by the addition of co-solvent to redissolve the CAQ, followed by heating to remove the co-solvent. The organosilicone gels were found to be indefinitely stable at ambient temperatures. By contrast, organic gels were stable from a few hours to a few weeks, with some being stable for several months (depending upon the gelling agent, its concen- tration, the solvent and the temperature of storage).' The greater stability of the silicone gels is attributed to the very poor solubility of the gelator in silicones compared with the organic solvents. (Cooling under cold running water or in the freezing compartment of a refrigerator was required for forma- tion of several of the organic gels.2) Gelation using Cholestanyl Anthraquinone-2-Carboxylate Similarly to CAQ, cholestanyl anthraquinone-2-carboxylate (CHAQ) was found to form gels with decamethylcycloprmtasi- loxane at the same concentration levels.1182 J. MATER. CHEM., 1994, VOL. 4 Table 1 Cholesteryl esters screened as silicone gelators compound" (mp/"C) gelator/solvent (wt.%) phase formation; comments I cholesteryl oleate (44.5) 5/mixture of octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and crystals after 2 days dodecamethylcyclohexasiloxane (Dow Corning 345 Fluid) I1 cholesteryl stearate (79-81) 5/Dow Corning 345 Fluid ppt.even when warm I11 cholesteryl nonate (80.5) 5/Dow Corning 345 Fluid slow crystal growth IV cholesteryl laurate (93) 5/Dow Corning 345 Fluid partial, very fragile, gel, soft semi-clear V cholesteryl cinnamate* (158-160) 5/Dow Corning 345 Fluid ppt. even when hot; star-like crystals fill most of the volume of the liquid VI cholesteryl phenylacetate* ( 110) 3.2 and 5/Dow Corning 345 Fluid; star-like crystals; opaque (white) gel polydimethylsiloxane (PDMS), viscosity 100 cSt VII cholesteryl anthraquinone-2- O.l-8/See Table 2 carboxylate (CAQ) VIII cholestanyl anthraquinone-2- 2/Dow Corning 345 Fluid carboxylate (CHAQ) IX cholesteryl (2-anthry1oxy)ethanoate' 2/decamethylcyclopentasiloxane; PDMS viscosity PPt.350 cSt X cholesteryl 4-( 2-anthry1oxy)- 2/decamethylcyclopentasiloxane; PDMS viscosity weak partial gel and crystals butanoate (CAB)' 350 cSt XI cholesteryl 1-pyrenebutanoate' 2/decamethylcyclopentasiloxane; PDMS viscosity PPt. 350 cSt XI1 cholesteryl 542-anthry1oxy)-2/decamethylcyclopentasiloxane; PDMS viscosity PPt. pentanoate (CAP)' 350 cSt XI11 2-anthryl lauryl ether' 2/decamethylcyclopentasiloxane; PDMS, viscosity PPt. 350 cSt XIV cholesteryl 2-naphthalene- 2/decamethylcyclopentasiloxane; PDMS, viscosity crystals ethanoates' 350 cSt xv cholesteryl 9-anthracenecarboxylate 2/decamethylcyclopentaciloxane PPt.(9-CAC)d "The general gelation procedure for compounds I-VI was to heat them in the silicone fluid until they dissolved or melted and then allow them to cool at ambient temperature. For the rest of the compounds a co-solvent such as CHCl, was used. bThe gelation process for these compounds was carried out with and without CHC13 as a co-solvent. 'Sample kindly donated by Prof. Weiss. dSynthesized in our labs (see Experimental section). Table 2 Reactive and non-reactive silicone fluids gelled by CAQ at 2 wt.% silicone fluid formula I octamethylcyclotetrasiloxane [(CH,)zSiOl4I1 decamethylcyclopentasiloxane [(CH3)2si015 I11 mixture of I1 and dodecamethylcyclohexasiloxaine [(CH3)2Si016IV hexamethyldisiloxane [(CH3 )3silzo V poly(dimethylsi1oxane) (PDMS)" (CH,),SiO [(CH,),SiO].Si(CH,), VI poly(methylphenylsiloxane)b (CH3 )3sio C(CH3) (c1jH5 )siol8(cH3 )3 VII silicone glycol co-polymer (CH3 )3si0 {(CH3)Zsio 1xiCH3 [C3H50 (C2H40)12H1 sio1y si(CH3 )3x=9, y=4 VIII poly(methylsi1oxane) (CH,),SiO [( CH3)HSiO]60Si(CH3)3 IX silicone amine copolymer (CH,),SiO [(CH3),SiO],(CH3 [CHzCH(CH3)CHzNHCH,NH,] SiO},Si(CH3)3 IXa: x=96, y=2; IXb: x=188, y=lO X poly (met h yloctadecasilane) (CH3)3SiO[(CH3),Si0]9,(CH3RSiO)5Si(CH3)3R = -CH2(CH,),,CH3 XI poly(decylmethylsi1oxane) (CH3)3Si0 [(CH3)2Si0]2 [Ch3RSiOl5Si(CH3), R = -CH2(CH2),CH3 XI1 poly(methyltrifluoropropy1siloxane) (CH3)3SiO(CH3RSiO)xSi(CH3)3R = -CH,CH2CF3 "Polymers with melt viscosities from 0.65 to lo000 cSt (M, 166-4oooO) were tested.*Two polymer fluids of melt viscosity 500 cSt: VIa, Dow Corning 710 Fluid and VIb Dow Coming 510 Fluid were tested. Structuresof CAQ Gels: Optical and Electron Microscopy [Fig. l(u),(b)]have domains with diameters between 50 and 100 pm. The individual fibres are considerably less than Transmitted (through cross-polarizers) and differential inter- 1 pm wide. ference contrast (DIC) modes were used during optical The gels are sheer-thinnable as shown in Fig. l(u),where a microscopy studies of the organosilicone gels. Fig. 1 shows channel of fluid is observed between the fibrous network. This the photomicrographs of various gel networks of 2 wt.% was caused by the disturbance of the gelator network when CAQ.In all cases the gel network appeared to be three the gel was placed between the coverslip and the microscope dimensional and interlocking and to consist of fibrous bundles slide. We believe that the gelator network is continuous emanating from central points. The structures are very similar throughout the fluid volume of an undisturbed gel. Cryogenic to those observed by Weiss et al. for the CAB-dodecene gels, scanning electron microscopy (SEM) was used to examine Maltese crosses (which are reminiscent of a liquid-crystalline the morphology of the individual fibres (see Fig. 2). Sample pattern)" are highly visible in Fig. 1(b). The approximate preparation (freeze-etching between -60 and -150"C at ca.dimension of these domains seems to be dependent upon the Torr for up to 1 h) has presumably removed the volatile silicone fluid and the concentration of CAQ. The gels with silicone phase. Both micrographs show the presence of 'end- silicone amine copolymer and dimethyl cyclic siloxanes less' fibres that intertwine to form a three-dimensional net- J. MATEK. CHEM., 1994, VOL. 4 Fig. 1 Optical micrographs of CAQ-silicone gels. (a) Gel of 2 wt.% CAQ in silicone amine copolymer (material IX in Table 2); (b)gel of 2 wt.% CAQ in mixed siloxanes (mixture of I, I1 and I11 in Table 2); (c) gel of 2 wt.% CAQ in poly(methylsi1oxane) (material VIII in Table 2). All gels viewed in DIC mode. Bar =50 pm.work. It is thought that this network immobilizes the silicone fluids uia weak intermolecular forces to form a gel. The morphology of the fibrous network is very similar to that described by Weiss et al. for the CAQ-dodecane, hexadecane and octan- 1-01 gels. The micrographs indicate that the diam- eters of the fibres range from ca. 0.1-0.5 pm. The number of fibres per unit volume increases with the gelator concentration. The 2 wt.% CAQ-Dow Corning 345 Fluid gel has very little free space between the fibres [Fig. 2(b)]. The 0.5 wt.% CAQ-decamethylcyclopentasiloxane gel has a lower density Fig. 2 Electron micrographs of (a) 0.5 wt.% CAQ-decamethyl-cyclopentasiloxane gel; and (b)2 wt.% CAQ-Dow Corning 345 Fluid. Samples were freeze-etched at -60 "C to -150"C at lo-' Torr for approximately 0.5-1 h.Bar= 1 pm. of fibres which appear to be smaller in diameter. The white specks visible in Fig. 2(u) are believed to be due to ice crystals from the sample preparation. The cryogenic SEM photomicrographs of non-volat ile sili- cone polymer gels showed only smooth and texture surfaces with no apparent fibrous structures present. Freeze-fracture techniques used to examine the internal structures of the polymer gels gave similar results. Portions of the same gels showed fibrous networks when viewed through an optical microscope where no special sample preparation was required. The low-temperature (from -150 to -160°C) and high vacuum freezing and etching process during SEM sample preparation appeared to destroy the fibrous CAQ structure when the gel matrix was a polymeric silicone fluid. Destivction of the network may be due to the low-temperature phase transitions of the siloxane fluid phase.Thermal Stability The stability of the gels at elevated temperatures was investi- gated by observing their phase changes during heating on a melting-point apparatus. All the silicone gels were found to be stable to over 100°C. Upon melting, the gels collapsed to a cloudy white mixture, eventually changing to a cleaI liquid (silicone fluid) with suspended CAQ crystals (mp of CAQ is 230 "C). Table 3 lists the approximate melt temperatures for several organosilicone-CAQ gels. The least stable gels were those made with silicone glycol copolymer (VII) and the poly(methylphenylsi1oxane)(VIb).These fluids are better ‘sol- vents’ for CAQ than the rest. The stability of the organosil- icone gels appears to be higher than that of the analogous gels of organic solvents reported in the literature’ due to the lower solubility of CAQ in silicones. Rheological Studies Initial qualitative observations suggested that most of the organosilicone gels were quite firm. For example, when a 2 wt.% CAQ-silicone amine copolymer (IXb) gel and a 2 wt.% CAQ-decamethylcyclopentasiloxane gel were exposed to vigorous agitation on a vortex mixer for 2min, they retained their consistency with no evidence of gel destruction. Rheological properties of some of the gels were investigated.Fig. 3 shows the dynamic complex viscosity changes of CAQ-decamethylcyclopentasiloxane gels as a function of the frequency of the applied strain. The data indicate that the dynamic complex viscosity of the gels increases with increasing CAQ content over the range of 1-8 wt.% CAQ. The dynamic viscosity of the gels was also shown to increase with PDMS fluid viscosity (from 5 to 10000 cSt) at a constant CAQ level (1 wt.%). Screening of other Cholesteryl Esters as Silicone Gelators In addition to CAQ and CHAQ, several other cholesteryl esters were screened as silicone gelators (see Table 1). CAB was the only one which showed the formation of a weak Table 3 Approximate temperature of phase change (‘melt’) for CAQ-silicone fluid gels silicone fluid” ‘melt’ temperature/“C silicone glycol copolymer (VII)b 120 poly(methylphenylsi1oxane)(VIa) 135 (Dow Corning 710 Fluid) decamethylcyclohexasiloxane (111) 145 poly(methylsi1oxane) (VIII) 166 PDMS (viscosity 350 cSt) (V) 170 poly(methylphenylsi1oxane)(VIb) 170 (Dow Corning 510 Fluid) silicone amine copolymer (IXa) 175 silicone amine copolymer (IXb) 176 nFormulae of fluids are listed in Table 2.bRoman numerals in parenthesis from Table 2. J. MATER. CHEM., 1994, VOL. 4 partial opaque gel (at 2 wt.%) when tested with decamethylcy- clopentasiloxane and PDMS (viscosity 350 cSt). The appear- ance of the gels was similar to that of a CAQ-PDMS gel with the exception that optical microscopy studies revealed the presence of needle-like crystals.Apparently only a portion of CAB formed the fibrous network responsible for the partial gelation, with the remaining CAQ crystallizing out. Fig. 4 shows the optical micrograph of a partial gel of decamethylcyclopentasiloxane-2 wt.% CAB in DIC mode. Other ALS cholesteryl esters provided to us by Prof. Weiss (compounds X-XIV) formed amorphous precipitates or crys- tals when used to gel silicone fluids. At the present time we can only speculate that this could be due to the process conditions as well as the lack of the characteristic features (whichever these may be) that are necessary for the cholesteryl compounds to become effective gelators of silicone fluids. During the gelation process, many of the cholesteric com- pounds in Table 1 formed large crystals (macrocrystals or macrofibres) that expanded through the whole volume of the silicone fluid either in the form of star-like structures or tree- branched structures.The most effective of these was cholesteryl phenylacetate 5 wt.% of which in Dow Corning 345 Fluid or PDMS (viscosity 100 cSt) was able to entrap all the volume of the silicone fluid. The ‘gel’ was white in appearance and upon inversion there was virtually no flow of liquid. The crystal growth in 5 wt.% cholesteryl phenyl-acetate-Dow Corning 345 Fluid and PDMS fluid mixtures was followed by optical microscopy using a video camera. Fig. 5 and 6 show the crystal growth in Dow Corning 345 Fluid and PDMS Fluid (10 cSt) using photographic stills from the video tape.The mixtures were heated to dissolve and melt the cholesteryl phenylacetate and a drop of the hot melt (mixture) was placed in the well of a microscope slide for viewing as it cooled. The photographs show that the two fluids induce two apparently different crystal-growth patterns. The cholesteryl phenylacetate in the Dow Corning 345 Fluid seems to crystallize in spherical-like patterns that originate from many nucleation sites. The crystal patterns eventually merge (or mesh) together and occupy all the fluid [Fig. 5(d)]. When PDMS is used as the ‘gelation’ matrix the crystal growth patterns are no longer spherically symmetrical but tend to grow asymmetrically, forming long branches; they also emanate from many nucleation sites (which are visible during the early phases of crystallization). These ‘nucleation’ sites disappear as the macrocrystals grow in their vicinity. The crystal growth stops in a particular direction when the ‘nucleation sites’ have been exhausted.At 5 wt.% the density frequencylrad s-’ Fig. 3 Dynamic complex viscosity vs. frequency of the applied strain curves for CAQ-decamethylcyclopentasiloxane gels. *, Jello; 0, Fig. 4 Optical micrograph of 2 wt.% CAB-decamethylcyclo-2 wt.% CAQ; A, 4 wt.% CAQ; 1,8 wt.% CAQ. pentasiloxane viewed in DIC mode. Bar =200 pm. J. MATER. CHEM., 1994, VOL. 4 1185 Fig. 5 Optical micrograph series of crystal growth of 5 wt.% cholesteryl phenylacetate in Dow Corning 345 Fluid. Bar= 140 prn of the macrofibres is high enough to immobilize and entrap all the PDMS fluid.Since cholesteryl phenylacetate was introduced into the silicone fluids without the use of a co-solvent, the ‘gelation’ process was reversible. Upon reheating a 5 wt.% cholesteryl phenylacetate-Dow Corning 345 Fluid ‘gel’, the solid phase dissolved, however, upon cooling it reformed and totally entrapped the silicone fluid. Two other cholesteric esters from Table 1, cholesteryl laur- ate (IV) and cinnamate (V) showed similar behaviour (although much less effective) to the cholesteryl phenylacetate. The former compound formed a hazy, partial, very fragile ‘gel’. The latter compound had very little solubility in the Dow Corning 345 Fluid and started precipitating in the form of microfibres immediately upon removal from the hot-plate.Star-like crystals grew to fill up almost the whole volume of the silicone fluid. Similar gels were obtained when CHC1, was used as a co-solvent to incorporate cholesteryl phenylacetate and cholesteryl cinnamate into Dow Corning 345 Fluid, followed by its removal via thermal treatment. A mixture of 3.2 wt.% cholesteryl phenylacetate and 12.8% CHC1,-PDMS (viscosity, 200 cSt) formed a solid firm phase with no fluid creeping after heating for a few seconds on a hot plate. The gelation process using these simple cholesteric com- pounds seems to be analogous to that of CAQ gelation but on a larger scale. The esters IV-VI form macrocrystals or macrofibres which seem to grow and organize upon cooling to fill the entire volume of fluid (depending upon concen- tration) while the CAQ and CHAQ compounds grow invisible microfibres (nanometres size) which create a dense network that immobilizes the silicone fluid and produces clear or semi-clear gels.The process of the crystal growth depends primarily upon the bulk solvent properties’* and the weak interniolecu- lar forces between the silicones and the cholesteric ester molecules, which in turn impact on their solubility characteristics. Even in the case of the CAQ gelator, crystals form when fluorosilicones were used as the matrix. The fluorosilicone fluid CH,=CH(CH,),SiO [(CH,)(CH2CH2CF,)SiO]20-25Si-(CH,),CH=CH, formed opaque paste-like gels with CAQ at 0.125, 0.25, 0.5 and 1 wt.%.Optical microscopy showed large needle-like crystals that seemed to entrap and immobilize the fluorosilicone fluid in a manner analogous to that of the cholesteryl phenylacetate. Controlled-stress rheology studies showed that the gel strength as well as the initial viscosity increased with CAQ concentration. The non-linear reduction in viscosity with increased sheer rate was attributed to sheer thinning. The gels were not thixotropic (they did not recover completely upon sheer thinning). Experimental Methods and Materials All silicone fluids were obtained from Dow Corning Corporation. All other chemicals were reagent grade (Aldrich, J. MATER. CHEM., 1994, VOL. 4 Fig. 6 Optical micrograph series of crystal growth of 5 wt.% cholesteryl phenylacetate in PDMS fluid (viscosity 10 cSt).Bar = 140 pm. Fischer Scientific and Lancaster Synthesis) and were used without further purification. Column chromatography" was performed on a 41 mm id chromatography colymn packed with 10.25 cm of dry silica gel (David silica 60 A, 35-70 pm, Altech Associates). Optical microscopy was viewed through a Carl Zeiss Axioscope Microscope, model D-7082 Oberkochen, in DIC and cross-polarization modes. The instrument was equipped with a 35mm photographic camera and a video camera attached to a VCR and monitor. Cryogenic SEM was performed on a JEOL 35CF instrument equipped with a cryogenic attachment from IEO Manufacturing. Synthesis of Cholesteryl Anthraquinone-2-carboxylate A modification of the preparation reported in the literature was used.' A three-neck 100 ml round bottom flask, equipped with a thermometer, condenser and N, line, was charged with 1.01 g (4 mmol) anthraquinone-2-carboxylic acid and 4.54 g (34.4 mmol) oxalyl chloride in 87 ml of dry tetrahydrofuran (THF); a slight exotherm (35-45 "C) was observed.The mixture was stirred and heated (45-50 "C) in a dry atmosphere for 1 h and stirred at ambient temperature for 16 h. THF and the excess of oxalyl chloride were removed on a rotary evaporator and the crude acid chloride, a yellow solid residue, was dissolved in 85ml of new THF and stripped a second time. The solid acid chloride was transferred to a Schlenk filter tube in a glove bag and washed with heptane three or four times in an inert atmosphere to remove residual oxalyl chloride.The anthraquinone-2-acid chloride was dissolved in dry THF (56 ml) and transferred to the reaction flask (under an inert atmosphere) for reaction with cholesterol. Cholesterol ( 1.55 g, 4 mmol) and 400 pl (5mmol) pyridine were added to the acid chloride-THF solution and the mixture was stirred for 16 h at ambient temperature. The product, CAQ, was soluble in the reaction solvent. Insoluble pyridine hydro- chloride was removed by filtration. CAQ was isolated as a yellow solid after removal of solvent on a rotary evaporator. Part of the unreacted anthraquinone carboxylic acid was selectively precipitated from a chloroform solution containing the product.CAQ was then recrystalized twice from a chloro- form-methanol solution, producing fluffy yellow crystals. The yield of pure CAQ was low using this method. Further purification was accomplished by column chromatography on silica gel. (The two main impurities anthraquinone-2- carboxylic acid and cholesterol, being more polar, were retained by the column.) Its characterization agreed with that reported in the literature.' Synthesis of Cholestanyl Anthraquinone-2-carboxylate A three-necked 100ml flask was charged with 1.01 g (4 mmol) anthraquinone-2-carboxylic acid and dissolved in 75 g THF. Oxalylchloride (2.54 g, 20 mmol) was added and allowed to react for 2 h at 45 "C and ambient temperature for 16 h. THF and the excess of oxalyl chloride were removed on a rotary thin-film evaporator.The product was washed with dry J. MATER. CHEM., 1994, VOL. 4 heptane in a Schlenk filtration apparatus and dissolved in dried THF. Cholestanol(l.41 g, 3.63 mmol) and 0.4 g pyridine were dissolved in 27g THF and added to the acid chloride and allowed to react for 20 h at room temperature. After filtration, the THF was removed with stripping and 1.63 g of a yellow solid (melting point, 18OOC) was recovered. The infrared (KBr pellet) spectrum showed the appearance of the ester carbonyl at 1724 cm-'. The material was further purified by column chromatography using a silica gel column. Synthesis of Cholesteryl9-Anthracenecarboxylate A three-necked 100ml flask equipped with a thermometer, condenser and N, line, was charged with 0.89 g (4mmol) 9-anthracene carboxylic acid and 2.59 g (20.4 mmol) oxalyl chloride in 28 ml of dry THF.The mixture was stirred and heated (45-50°C) in a dry atmosphere for 2 h. THF and the excess of oxalyl chloride were removed on a rotary evaporator and the crude acid chloride was washed with heptane four times in an inert atmosphere. The acid chloride (0.71 g) was then allowed to react with 0.71 g (2.95 mmol) cholesterol in dry THF in the presence of 0.43 g (5 mmol) pyridine. The product (mp 195 "C) was isolated after removal of the solvent on a rotory evaporator. General Test Method for Gelation of Silicone Fluids Using CAQ CAQ (0.01 g) was weighed accurately (tok0.1 mg) into a glass sample vial.An amount of 0.5 gkO.01 silicone fluid was added to the vial. Chloroform (ca. 2g) was added until the CAQ dissolved. The homogeneous solution was heated on a hot-plate to evaporate the chloroform. The weight of the sample was monitored to determine the amount of chloroform remaining. A gel was formed when the chloroform remaining in the solution was <0.02 g. As mentioned in the discussion, some gels formed while still on the hot-plate. The gelation was considered successful when upon inversion there was no fluid running down the walls of the vial. We thank Dr. Lauren Tonge and Mr. Mark Fisher of Dow Corning Corporation for their assistance with the optical microscopy and the rheological studies, respectively. We also acknowledge Professor Stanley Flegler of Michigan State University for his help with the cryogenic SEM.We are grateful to Professor Richard G. Weiss of Georgetown University for providing the ALS gelator samples and his valuable comments. This work was supported by Dow Corning Corporation. References 1 Y-C. Lin, B. Kachar and R. G. Weiss, J. Am Chem. SOC, 1989, 111,5542. 2 Y-C. Lin and R. G. Weiss, Macromolecules, 1987,20,414. 3 R. G. Weiss and V-C. Lin, U.S.Patent 4,790,961, 1988. 4 K. Hanabusa, J. Tonge, Y. Taguchi, T. Koyama and H. Shirai, J. Chem. SOC., Chem. Commun., 1993,390. 5 K. Habusa, K. Okui, K. Karaki, T. Koyama and H. Shirai, J. Chem. SOC.,Chem. Commun., 1992,1371. 6 M. Aoki, K. Murata and S. Shinkai, Chem. Lett., 1991,1715. 7 F. R. Taravel and B. Pfannemuller, Makromol. Chem., 1990, 191, 3097. 8 T. Tachibana and H. Kambara, Bull. Chem. SOC. Jpn., 15169, 42, 3422. 9 T. Tachibana, S. Kitazawa and H. Takeno, Bull. Chem. Sic. Jpn., 1970,43,2418. 10 T. Tachibana, K. Kayama and H. Takeno, Bull. Chem. Soc. Jpn., 1972,45,415. 11 T. Tachibana and H. Kambara, J. Am. Chem. Soc., 1965,87,3015. 12 P. Terech, R. Ramasseul and F. Volino, J. Colloid Interface Sci., 1983,91,280. 13 R. H. Wade, P. Terech, E. A. Hewat, R. Ramasseul and F. Volino, J. Colloid Interface Sci., 1986,114,442. 14 P. Terech, Mol. Cryst. Liq. Cryst., 1989, 166,29. 15 T. Broth, R. Utermohlen, F. Fages, H. Bouas-Laurent and J-P. Desvergne, J. Chem. SOC., Chem. Commun., 1991,416. 16 D. M. Blow and A. Rich, J. Am. Chem. SOC.,1960,82,3566 17 D. Demus and L. Richter, Textures of Liquid Crystals, Verlag Chemie, Weinheim, 1978. 18 I. Furman and R. G. Weiss, Langmuir, 1993,9,2084. 19 W. C. Still, M. Kahn and A. Mitra, J. Org. Chem., 1978,43. 2923. Paper 4/001721; Received 11th Januar;,?,1994

ISSN:0959-9428    

DOI:10.1039/JM9940401181

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(8), 1189-1193 Interfacial Chemistry and Mechanical Effects of a Multifunctional Processing Additive on Carbon Black Filled Rubber Robert H. Bradley,* Enshan Sheng, Ian Sutherland, Philip K. Freakley and Hanafi Ismail+ University of Technology, Loughborough, Leicestershire, UK LE?I 3TU The interfacial effects of a multifunctional additive (MFA), the n-tallow-propane-l,3-diamine salt of carboxylic acid, on carbon black filled rubber have been studied. The surfaces of three normal-cure-rate carbon blacks, of differing nitrogen BET surface areas, were characterised by X-ray photoelectron spectroscopy (XPS) and vapour-phase chemical derrvatis- ation and found to contain very few functional groups. The MFA has been found to decompose at ca.120 "C and the decomposition to generate diamine and a carboxylic acid species. Bound rubber, determined by o-xylene extraction, was found to decrease with the addition of MFA and a limiting bound rubber value was obtained at the MFA loading that corresponds to a monolayer coverage of the carbon black surface. The reduction of bound rubber with the addition of MFA is attributed to the release of rubber, immobilised within carbon black agglomerates, as a result of improved dispersion. The mechanical properties of the rubber were also found to improve with the addition of MFA and again this was attributed to the dispersing effect of the MFA on the carbon black. Optimum mechanical properties were observed at an MFA loading which approximately corresponds to a monolayer coverage of the carbon black surface.It has been shown that the n-tallow propane-1,3-diamine salt of a carboxylic acid having the general formula [RNH;(CH2),NH:][R'C0,1, enhances the mechanical properties of carbon black filled natural and synthetic rub- ber~.'~~This surfactant has been termed a multifunctional additive (MFA) since it is observed that it can function as a processing aid, a filler dispersant, a cure accelerator and a mould-release agent. To use this MFA effectively in the rubber industry, it is important to understand the resultant interfacial effects between the filler and the elastomer and also the effects of the MFA on the bulk mechanical properties of the rubber. In this study XPS and FTTR were used to characterise the surfaces of a series of carbon blacks and the MFA itself.The blacks chosen have differing specific surface areas, measured by nitrogen BET, as shown in Table 1; this allows the amount of carbon surface available for interface formation to be varied. Bound rubber has also been assessed since this gives a measure of the degree of interaction between the carbon black surface and the rubber and how this interaction is modified by the presence of the MFA. In this study bound rubber is regarded as the rubber component of an unvulcan- ised mix, which is strongly associated with the filler surface and which cannot be removed by a specific period of solvent extraction. This bound rubber may include rubber that is strongly adsorbed onto the black surfaces and that is physi- cally trapped within the voids of the carbon black agglomer- ates; the latter material is sometimes termed 'immobilised rubber'.A schematic diagram showing the terminology used in this work is given in Fig. 1. o-Xylene, which is a good solvent for natural rubber, was used as the solvent for bound t On study leave from Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia. Table 1 BET specific surface areas (by N, adsorption) and XPS analysis results of several carbon blacks carbon black N115 N330 N550 atom% surface area/m2 g-' C 0 S 139.5 98.9 0.6 0.5 78.0 98.6 0.9 0.5 38.9 98.5 0.9 0.6 carbon black agglomerate im'mobilised rubber Fig. 1 Schematic representation of immobilised rubber within a carbon black agglomerate.The agglomerate is composed of loosely bound aggregates of fused carbon black primary particles rubber determination in this study. The effects of the MFA on the mechanical properties of vulcanised rubber were also investigated. Experimenta1 Materials Table 2 lists the compounding materials, their manufacfurers and the levels used. Various levels of the MFA, expresxed as parts per hundred parts of rubber by weight (pphr), were incorporated to study the concentration effects. Sulfur is added as a cross-linking, i.e. curing, agent. Zinc oxidt: and stearic acid act together as a cure activator, CBS (N-cyclohex- ylbenzothiazole-2-sulfenamide) is a cure accelerator and Flectol-H ( 1,2-dihydro-2,2,4-trimethylquinoline)is an an tioxi- Table 2 Formulation used in rubber mixing material manufacturer formulation ( pphr) natural rubber (SMR20) Malaysia carbon blacks Cabot zinc oxide Union Minere Oxide (Belgium) stearic acid Caldic UK Ltd.sulfur Schill & Seilscher CBS Monsanto Flectol H Monsanto MFA, EN444 Akzo 100.0 50.0 5.0 3.0 2.5 0.5 1.o 0.0-5.( 1 1I90 dant. Mixing was carried out using a Francis Shaw K1 Intermix. After it had been mixed, each batch was sheeted off to ca. 3 mm thickness, which is suitable for subsequent preparation of mechanical test specimens. Carbon black BET specific surface areas were determined by nitrogen adsorption at 77 K using a Micromeritics automated ASAP2000 multi- point BET instrument.Analytical-grade o-xylene, for bound rubber measurement, was supplied by Fisons Chemicals. Vapour-phase derivatisation reagents, i.e. trifluoroacetic anhydride (99 + YO),trifluoro-ethanol (99 +%), pyridine (99+YO)and 1,3-di-tert-butyl-carbodiimide (99%) were all obtained from Aldrich. XPS, FTIR and SEM XP spectra were recorded on a VG ESCALAB MK1 spec- trometer. Surface compositions were calculated from elemental peak areas, after subtraction of a Shirley-type background, using Scofield photoelectron cross- section^.^ Correction was made for the inelastic mean-free path of the photoelectrons in the solid,6 for transmission of the energy analyser7 and for the angular asymmetry of the photoemissions.' Chemical derivatisation of hydroxy and carboxylic acid groups was performed at controlled vapour pressures of trifluoroacetic anhydride and trifluoroethanol respectively, in a vacuum frameg according to the following: 00 0 n 0 Derivatisation of hydroxy groups was allowed to proceed for 2 h.Carboxylic acid groups were derivatised for 12 h in the presence of pyridine and 1,3-di-tert-butylcarbodiimidesince previous work had established that no further increase in surface fluorine concentration with reaction time occurred after 10 h using poly(acry1ic acid) as a model surface." A Nicolet 20 DXC FTIR spectrometer was used to record IR spectra. The MFA was mixed with KBr and pressed into a disk. IR spectra were recorded at different temperatures, which were controlled using an in situ temperature cell.Scanning electron microscopy (SEM), used to examine the carbon black dispersion, was carried out using a Cambridge Stereoscan 360 instrument. Measurement of Bound Rubber The bound rubber was measured by immersing ca. 0.25 g of an unvulcanised rubber mix, diced into pieces, into 50 cm3 of o-xylene in a wide-mouthed glass bottle. The bottle was then sealed and left for 10 days at room temperature. It had previously been shown that under these conditions the meas- ured bound rubber decreased with extraction time up to ca. 10 days, after which no further decrease was observed. After this period of extraction the rubber pieces were taken out and thoroughly dried in a vacuum oven at 40 "C and thermogravi- metrically analysed using a Stanton Redcroft TG-750.For these measurements a 10mg sample was purged in nitrogen and then heated at a rate of 50°C min-l and the loss in weight was monitored with a chart recorder. Each sample was first heated in nitrogen and then air. The weight loss in nitrogen corresponds to rubber and processing aids, which are normally difficult to resolve in the pyrolysis curve, whilst the weight loss in air corresponds to carbon black. The ratio between the two weight values (ie.grams of bound rubber J. MATER. CHEM., 1994, VOL. 4 per gram of carbon black) was taken as the bound rubber in this study. Results and Discussion Surface Characterisation of Carbon Blacks Surfaces of three carbon blacks were studied.XPS results show that all of the surfaces are effectively carbon with very low levels of oxygen and sulfur as shown in Table 1. Diffuse- reflectance Fourier-transform infrared (DRIFT) spectra were also recorded, but no functional groups were detected, suggest- ing that the oxygen- and sulfur-containing species may only be present in the near-surface region of the carbon black structute since XPS has a much shallower sampling depth (ca. 50 A) than DRIFT (ca. 1pm). High-energy resolution C 1s spectra were recorded and deconvolved to remove the broad- ening effects of the A1-Ka X-ray line shape. The spectra so obtained show no evidence for chemically shifted peaks, which indicates that the near-surface concentration of the individual functional groups is below the detection limit of the experi- ment.To increase the sensitivity and to identify these individ- ual species, chemical derivatisation was used. The reactions described label the OH and C02H each with three fluorine atoms, which, since the photoionisation cross-section of F is a factor of four greater than that of C (which determines the sensitivity in the C 1s spectrum), should give a ca. 12-fold increase in sensitivity. Surface hydroxy and carboxylic acid concentrations can then be estimated from fluorine atomic levels. The results obtained are shown in Table 3. The method reveals some OH groups on the carbon black surfaces, but there appear to be very few C02H groups.Although the derivatisation technique for acid groups has been found to work on polymer surfaces," it may not be applicable to carbon black surfaces either because of the differing reactivity of the C02H when attached to the carbon surface, which comprises largely graphitic ring structures, or because the acid groups are positioned within surface pores that are too small to admit the tagging agent and allow chemisorption to occur. The lack of reactivity of carbon black surface C02H groups toward trifluoroethanol was confirmed using a sample of the N330 black, which had been oxidised using nitric acid (increasing the surface oxygen concentration from 0.9% for the pre-oxidised sample to 8.0% after oxidation). The C 1s peak envelope from this material contained a prominent peak at a shift of +4.5eV from the main C-C/C-H peak (at 284.6eV), which is consistent with the presence of C02H.However, no acid groups were detected using the derivatis- ation technique described. Thermal Stability of MFA The thermal stability of the MFA (EN444) was studied using IR with an in situ temperature cell. Spectra (between 1000 and 1900 cm-l) taken at differing temperatures, are shown in Fig. 2. They show that the MFA gives structures characteristic of a typical amine salt of carboxylic acid, and is thermally stable up to ca. 120°C. Thereafter changes in peak structure Table3 Surface OH and C0,H concentrations of several carbon blacks as determined by vapour-phase derivatisation carbon black N115 N330 N550 concentration (atom%) of surface oxygen 0.6 0.9 0.9 concentration (atom%) of surface oxygen present as OH 0.3 0.2 0.6 concentration (atom%) of surface oxygen present as C0,H 0.0 0.2 0.0 J.MATER. CHEM., 1994, VOL. 4 I\ . L----L 100°C 1900 1675 1450 1225 1000 wavenum ber/cm-' Fig. 2 IR spectra of MFA at various temperatures and intensity occur as the temperature is raised and thermal decomposition proceeds. This is characterised by the decrease of peaks at 1558 cm-' (NH;/NHl) and 1400 cm-' (COT), and the increase, at a wavenumber of 1714 cm-',of the C02H peaks. There is little change in spectra recorded at tempera- tures & 170"C, suggesting that above this temperature the detectable decomposition is effectively complete.According to the spectral data the decomposition of the MFA appears to proceed as follows: RNH,f(CH,),NH;( RC0,)2+RNH(CH2)3NH2 +2R'C02H It has been demonstrated that the diamine can act as a vulcanisation activator or accelerator, while the carboxylic acid can act as an internal flow additive and also a mould- release agent.' Bound Rubber Measurement Fig. 3 shows the effects of the MFA loading on bound rubber of N330 filled compound, determined by o-xylene extraction. -5" I \" 2 0.41 0123456 EN444 loading Fig. 3 Effect of MFA loading on bound rubber of N330 determined with o-xylene extraction at room temperature It is notable that the bound rubber decreases with increasing MFA concentration, suggesting that the MFA weakens the interfacial interaction between the carbon black and the rubber molecules. Fig.4 shows SEM micrographs of rubber mixes which contain differing levels of MFA. They show that the control mix (no MFA) contains a larger number of undispersed carbon black agglomerates, and that the d isper-sion of these improves with the addition of MFA up to 2 pphr. Further increases in MFA loading above 2 pphr do not appear to give any corresponding improvement in carbon black dispersion. Therefore it is concluded that the reduced inter- action between the carbon black and the rubber, owing to the presence of the MFA, aids the breakdown of carbon black agglomerates at the mixing stage. The decrease of bound rubber with the addition of MFA could then be explained in terms of the release of immobilised rubber situated within the carbon black agglomerates (Fig.1). The amount of this immobilised rubber, which is measured as part of bound rubber, depends not only on the structure of the carbon black but also on the efficiency of breaking down the agglomerates during mixing. Further increases in MFA loading above 2 pphr have no effect on bound rubber. The precise mechan- ism(s) of this interfacial energy modification and the mode of carbon black attrition is currently being studied in detail and the findings of this work will be reported in future communi- cations. Using the BET surface area, shown in Table 1,50pphr of N330 would have an area of 3900m2. We calculate the approximat: projected geometric area of the MFA molecule to be 293 A2 and therefore a loading of ca.1.9g (which corresponds to approximately 2pphr) is required to give a monolayer coverage of the black assuming that the molecules are adsorbed onto the black surface flat rather than end-on. Mechanical Properties The tensile strength and 300% modulus of N330 filled rubber vulcanisate are plotted against the MFA levels in Fig. 5. They show that with the addition of MFA, both properties are improved by up to 10%. This is believed to be due to the improved dispersion of carbon black. For N330 the mechan- ical properties increase with MFA loading and reach maxima at ca. 2 pphr which, as shown, corresponds to an approximate monolayer coverage of the carbon black surface.Further increases in MFA loading are not accompanied by correspond- ing increases of the carbon black dispersion. Excessive MFA addition may produce a weak boundary layer at the interface between the rubber and the carbon black, possibly by forma- tion of a multimolecular layer, or may result in modification of the bulk properties of the rubber, leading to a reduction in mechanical properties. Behaviour similar to that described above has been observed for the other two carbon blacks (N115 and N550), which are of different surface areus. In these instances the peaks in mechanical properties shift to the MFA loadings which correspond to the respective monolayer equivalents of MFA. o-Xylene extracts of unvulcanised N330 filled rubber mixes were analysed using FTIR and peaks from the MFA were found to appear as the MFA loading exceeded 2pphr and progressively increase in intensity as more MFA was added to the mix.This suggests that the excess of MFA molccules are weakly bound at the carbon black/rubber interface and/or are incorporated into the bulk rubber where they can be physically extracted by the o-xylene. Conclusions Only low levels of oxygen and sulfur were detected on the carbon black surfaces by XPS. Low levels of hydroxy groups J. MATER. CHEM., 1994, VOL. 4 Fig. 4 SEM micrographs of rubber mixes with various MFA loadings (pphr): (a) 0.0, (b)0.3, (c) 1.0, (d) 2.0, (e) 3.0. (f)5.0 are indicated by chemical derivatisation, but the method used to tag carboxylic acid functionalities appears to be suspect.The chemical inertness of the carbon black surface, probably due to the presence of large areas of basal plane, suggests that the interaction between the carbon black and the MFA is probably physical and of the dispersion type. The MFA has been found to decompose at ca. 120"C,and the decomposition is complete at ca. 170°C. Diamine and carboxylic acid are generated by the decomposition process. The diamine can subsequently function as a vulcanisation activator or acceler- ator, while the carboxylic acid can function as an internal flow additive and a mould release agent. Bound rubber, measured in o-xylene, appears to decrease with the addition of MFA to a limiting value of ca.2 pphr for N330. This corresponds to an approximate monolayer coverage for this carbon black. The decrease in bound rubber was attributed to the release of immobilised rubber located within carbon black agglomerates which are shown by SEM to be better dispersed and broken down when the MFA is present. No further improvement in dispersion was observed after a mono- layer coverage of the carbon black surface (cn. 2 pphr for N330). The mechanical properties of vulcanised N330 filled rubber were improved by incorporating the MFA in the formulation. These properties appear to be optimal at MFA levels that correspond to monolayer coverage of the blacks. These improvements in mechanical properties appear to be J. MATER.CHEM., 1994, VOL. 4 27 I I19 Fig. 5 EffecL of MFA loading on tensile strength and 300% modulus of N330 filled vulcanised rubber attributable to the improved dispersion of carbon black in the rubber matrix. Again the optimum level was found to correspond approximately to the amount needed for a mono- layer coverage of the carbon black surface. The authors acknowledge the financial assistance of SERC (ES) and the Malaysian Public Service Department/Uni\ ersiti Sains Malaysia (HI). They also thank Mr. F. Page of IPTME/LUT for operating the SEM instrument. References 1 C. Hepburn and M. S. Mahdi, Plast. Rubber Process. Appl.. 1986, 6, 247. 2 C. Hepburn and M. S. Mahdi, Plast. Rubber Process. Appl.. 1986, 6, 257. 3 C. Hepburn and M. S. Mahdi, Plast. Rubber Process. Appl.. 1986, 6, 267. 4 C. Hepburn and M. S. Mahdi, GB Patent PCT.GB84/00148, 16 May, 1984. 5 J. H. Scofield, J. Electron Spectrosc. Relat. Phenom., 1976,8. 129. 6 M. P. Seah and W. A. Dench, Surf. Interface Anal., 1979,1, .!. 7 M. P. Seah, Surf Interface Anal., 1980,2,222. 8 R. F. Reilman, A. Msezane and S. T. Manson, J. Eltaron Spectrosc. Relat. Phenom., 1976,8, 389. 9 E. Sheng, Ph.D. Thesis, Loughborough University of Tech-nology, 1992. 10 R. P. Popat and I. Sutherland, unpublished results. Paper 4/00295D; Received 17th January, 1994

ISSN:0959-9428    

DOI:10.1039/JM9940401189

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994,8(4), 1195-1200 Aggregation Control by Vapour Phase and Heat Treatments in Langmuir-Blodgett Films of Amphiphilic Heteroarylazo Dyes Nobuhiro Kuramoto” and Masao Danbt a Division of Organic Materials, Osaka Prefectural Industrial Technology Research Institute, 2-1-53, Enokojima, Nishi-ku, Osaka 550, Japan Osaka Institute of Technology, 5- 16-7, Ohmiya, Asahi-ku, Osaka 535, Japan The effects of heat treatment (HT), and acidic- and basic-vapour-phase treatments (AT and BT, respectively) have been studied on Langmuir-Blodgett (LB) films of 2-[4-(octadecylamino)-l -naphthylazo]-N-methylbenzothiazolium perchlorate (azo V) and 2-[4-(dioctadecylamino)-1-naphthylazo]-N-methylbenzothiazoliumperchlorate (azo VI). The as-deposited films for azo V and azo VI exhibit an H-like aggregate band at 419 and 427 nm, respectively. After HCI vapour treatment, the H-like band for azo V disappears to produce monomeric (M) band at 563 nm.The film, which dissociated under AT treatment, exhibited an H*-like band (at 480 nm) that differed from the original H-like band after HT, and also exhibited a band at ca. 429 nm after BT (exposure to NH, vapour). A combination of two different treatments, i.e. AT+HT gives a reversible change between M and H*-like states. Similar optical changes were also obtained for azo VI films. Comparison of infrared (IR) spectroscopic measurements with transmission and reflection-absorption spectra of azo V in the LB films after AT and HT gave characteristic information due to the H- and H*-like aggregations and the monomer state.Apart from evidence for gas-vapour penetration into the LB films under the employed conditions, the IR spectra of the films correlate closely with the corresponding visible absorption spectra. Certain amphiphilic functional dyes are known to form differ- ent types of aggregates in both Langmuir-Blodgett (LB) films and bilayer rnembrane~.’~~ H- or H*-aggregates are charac- terized by an absorption band that is shifted to shorter wavelength (hypsochromic) relative to the monomer absorp- tion. Aggregates with absorption maxima at longer wavelength (bathochromic) are known as J-aggregates. Reversible processes, due to chromophore rearrangements, are caused by the peculiar solid-solid transitions in LB films and offer some interesting industrial applications, including electrical and optical devices.Previous investigations have focused on processes such as photochromism,5~8-’0 thermoch- romism6 and solvatochromism’’ in merocyanine and spiropy- ran LB films. In one class of azo dyes, it has been reported that azobenzene-containing amphiphiles exhibit spectral changes based on heat,7”1 light,12,13 and acidic- or basic-treatment^.^"^ However, for new types of azo dye, other than azobenzene derivatives, such processes have not yet been examined. In this paper, the reversible nature of the spectral changes of heteroarylazo dyes, 2-[ 4-(mono- or 2-[ 4-dioctadecyl-amino)-1-naphthylazol-N-methylbenzothiazolium perchlor-ates (hereafter referred to as azo V and azo VI, respectively) caused by heat (HT), acidic-vapour (AT) and basic-vapour (BT) treatments were investigated in the LB films.Experimental Materials Azo V and azo VI (see Fig. 1) were prepared from 3-methyl benzothiazol-2( lH)-one hydrazone hydrochloride and the corresponding N-octadecylated naphthylamine derivatives as described previ0us1y.l~ These dyes were purified by column chromatography on silica gel using chloroform as eluent. Satisfactory data were obtained for these compounds by elemental analyses and thin-layer chromatography. Azo V and VI showed visible absorption bands (Amax in methylene t Present address; Nihon Yupuro Co. Ltd., Higashinada-ku, Kobe 658, Japan. AzoV:R=H FUO VI:R = CleH37 Fig.1 Chemical structures of amphiphilic heteroarylazo d>’es chloride at 620 (E =1.20 x lo5) and 619 nm (E =9.5 :< lo4) respectively. Elemental analyses for azo V, Found: C, 63.8; H 7 5; N, 8.0%. Calc. for C36H51N404SCl: C, 64.4, H 7.7, N 8 35%. Elemental analyses for azo VI, Found: C, 69.5; H, 9.0; N, 6.45. Calc. for C,4H87N404SCl: C, 70.0; H, 9.5; N, 6.1%. Procedures A Kyowa Kaimen Kagaku model HBM-AP Langmuir tool with a Wilhelmy balance was employed for the n-A isotherm measurements as well as LB film fabrications. Several drops of chloroform solution (2 x mol dmP3) of azo V or azo VI were placed onto aqueous sub-phase containing 1.4x mol dm-3 CdCl, and 1.7 x loP5mol dm-3 NaHCO, (pH 6.3). After evaporation of the solvent, the monolayer was compressed at a constant rate of 20 cm2 min-’ up to a surface pressure of 22 mN m- ’.The monolayers were transferred onto quarz plates by the vertical dipping method at dipping and raising speeds of ca. 10 and 5 mm niin-’, respectively. The transfer ratio was found to be near unity (0.89&0.02) throughout the experiments. All the LB films treated in this paper have a Y-type structure with the first layer in the ‘head- on’ configuration. The three treatments, HT, AT and BT, were carried out as secondary treatments. For HT the samples were kept at ca. 80-90 “C in an atmosphere of air for 15 min. AT required exposure to vapour from a 35% HC1 aqueous solution in a vessel for 10 s. BT required exposure to vapour from a 28% aqueous NH3 solution in a vessel.BT treatment was also carried out by dipping the samples into an aqueous solution of 0.05 mol dmP3 NaOH. Absorption spectra were recorded on a Shimadzu UV-250 spectrophotometer. Infrared (IR) spectra of the LB films were recorded with 4 cm-' resolution on a JEOL JIR-100 FT-IR spectrometer equipped with an MCT detector. For the ZR reflection-ab- sorption (RA) measurements, a JEOL IR-RES 110 reflection attachment was employed at the incidence angle of 80". The LB films were transferred onto CaF, plates for the IR trans-mission measurements and onto Au-evaporated glass slides for the RA measurements. In general, several hundred scans were accumulated to achieve an acceptable signal-to-noise ratio.Results and Discussion Monolayer Characteristics Azo V and VI form stable condensed monolayers at the air/ water interface as can be seen from the measurements of the n-A isotherms (Fig. 2). At 17 'C the monolayer of azo V [Fig. 2(a)] is expanded and collapses at 27 mN m-' with an average monolayer area of 42A2 moleculeP1. For azo VI [Fig. 2(h)] the monqlayer collapses at 26 mN m-l and the occupied area is 48 A2 molecule-'. Thus, the areas occupied and pressure of collapse are almost the same for the two dyes. It is assumed thFt the ?rea peromolecule of the chromophore parts is ca. 82 A2 (13 A x 6.3 A) by using a molecular scale model. The values obtained from the n-A curves were smaller than those calculated by molecular size.This suggests that the long axis of the chromophore is neither perpendicular nor parallel to the air water surface, but exists with some inter- mediate angle. The detailed orientation of the dye molecules at the air/ water surface is attained by using the limiting area index and the angle I3 to the horizontal axis. The areas are consistent with the orientation of the dye molecules. It found that a monolayer of azo V has an orientation degree of ca. 54" to the water surface. The degree (I3=59") of orientation in the monolayer of azo VI is slightly larger than that for the azo V monolayer. Formation and Absorption Spectra of LB Films Fig. 3 shows visible absorption spectra of LB films that deposited on quarz plates (10 mm x 40 mm x 1 mm).The I I 0 0.25 0.5 0.75 area/nm molecule-' Fig. 2 Surface pressure-area isotherms for: (a) azo V; and (b) azo VI. Temperature, 17 "C; and pH 6.3 J. MATER. CHEM., 1994, VOL. 4 L 1 - I --.__-__-__-- 400 600 800 wave lengt h/n m Fig. 3 Absorption spectra of (a) freshly prepared LB film of azo V; (b) azo V in chloroform solution; (c) freshly prepared LB film of azo VI; and (d) azo VI in chloroform solution optical absorption spectrum of the azo V LB film with 22 monolayers exhibits an H-like band at 419 nm [Fig. 3(a)]. Since the same material in the 1x lo-' mol dm-3 chloroform solution exhibits an absorption peak at 595 nm, the H-like band in the LB film is shifted towards the blue by 176nm. Similarly the absorption spectrum of the azo VI LB film with 22 monolayers exhibits an H-like band at 427 nm; however, the spectrum reveals a shoulder at 497 nm [Fig. 3(c)].Spectral Changes with Various Treatments The as-deposited film (just after deposition) from azo V is yellow, which is associated with a pronounced band at 419 nm under the present preparation conditions. This band may result from the formation of an H-like aggregate of the dye compound. Fig. 4 shows the effects of various treatments on the azo V film. The H-like band in the as-deposited film is dissociated (a) 595 I I I I I 400 600 wavelengthhm Fig. 4 Spectral changes for azo V films caused by the application of AT and HT: (a) reference in chloroform solution; Ib) the as-deposited reference (H-like: yellow state); (c) after AT for 30 s with 38% HCI vapour (M state: bluish violet); and (d) after AT-HT for 15 min at 90 "C (H*-like state: yellow-orange) J.MATER. CHEM., 1994, VOL. 4 by the AT treatment, and the film changes to bluish violet. The LB film exhibits a broad band at ca. 563nm as shown in Fig. 4(c), whereas a cast film prepared from a chloroform solution of azo V reveals a band at 562 nm. This change can therefore be attributed to the restoration of the monomeric state (M) from the H-like state. The film, after becoming bluish violet from the AT treat- ment, turns yellow-orange again on the application of HT, as seen in Fig. 4(d). This yellow-orange state (H*), however, is different from the as-deposited state.This suggests that the each spectrum involves at least two different H-like states, one at ca. 418 nm and the other at ca. 480 nm. Similar observations were also obtained for azo VI films. Fig. 5 shows the results of spectral changes for various treat- ments of the LB films of azo VI. In this case, the H-like band (422 nm) in the as-deposited film was dissociated by AT treatment to the monomeric state (557 nm), which returned to the H*-like state (around 475 nm) after HT. Fig. 6 shows the temperature dependence of the absorbance of the restored monomer band, which turns to an H*-like band during HT over a constant 15 min. The changes in the Ir 1 1 400 600 800 wavelengthhm Fig.5 Spectral changes for azo VI films caused by the various treatments.For definitions of (a)-@)see Fig. 4 560 # O 400 600 800 wavelength/nm Fig. 6 Temperature dependence on re-aggregation of monomer band once dissociated in the 22-monolayer azo V film. Heating time, 15 min. Temperature: (a) 50; (b)60;(c) 70; (d) 80; (e) 90; and (f)100"C. absorbance for azo V films are illustrated against heating at different temperatures (50-100 "C). An isosbestic point is recognized at about 495 nm in the figure. At 80-90 'C, the change was the most successive, These changes are obtained temporarily by BT (instead of HT), but it was difficult to monitor the behaviour beciause of the rapid transformation from the bluish violet to the yellowish state. On the other hand, the spectral change from an MtH or H* transition with BT (dipping for 60s into an aqueous solution of 0.05 mol dm-3 NaOH and then drying) could be monitored.In this case, the absorption spectrum revealed a broad band at ca. 429 nm. The result for the azo V lilm is shown in Fig. 7. Reversible Cycle by Combination of Two Different Trea trnen ts The films, having been coloured bluish violet after AT, turn yellow-orange after HT and show an H*-like band at ca. 480 nm as shown in Fig. 4. The growth of the H*-like band tends to be at a maximum within 15 min. It was found that the changes in colour between bluish violet and yellow-orange are reversible in the present film. The spectra after the first AT and HT are almost reproduced by the second AT and HT, respectively.Fig. 8 shows an example of the course of the spectral change (H,H*eM) on the azo V film traced by repeated application of the cyclic treatments (HT and AT). In Fig. 8, each difference in the absorbances at A,,, 553 nm and A,,, 480 nm after these treatments gradually decreases with the number of the cycles. After only 30 cycles, the differences can easily be seen; however, the mechanism for the gradual decomposition was not examined in present work. Similar observations were also recognized for the LB films of azo VI. Furthermore, reversible changes in the colour also take place for the AT+BT combination, i.e. the films, having turned bluish violet after AT turned yellowish (Ibmax429 nm) as a result of BT (dipping for 60 s into an aqueous solution of 0.05 mol dm-3 NaOH and then drying).The absorbance differences at each Amax between the two treatments for the azo V film kept over 75% in even after 30 cycles. The films derived from azo VI could be subjected to repeated cycling about 30 times without significant loss of the function. The above results for the optical measurements can be summarized as follows: (i) the H-like band in the as-deposited (b) 567 400 600 800 wavelengthhm Fig. 7 Spectral changes for azo V films caused by successive AT-tBT cycles. (a)As-deposited reference; (b)after AT (38% HCl vapour-); and (c) BT (dipping into 0.05 mol dm-3 NaOH solution for 60 s) after AT. J. MATER. CHEM., 1994, VOL. 4 1 10 20 number of repeating cycle Fig.8 Repeating cycle for an azo V film (AT and HT). The ratios (%) were calculated from the absorbances at 480 (I respectively films is dissociated to give a monomer band (M) by AT; (ii) the films that have turned bluish violet (M state) after AT, exhibit an H*-like band on application of HT; (iii) a combi- nation of two different treatments, i.e. AT+HT+AT exhibits reversible changes between the M state and H*-like state; (iv) instead of HT, application of BT also gives reversible changes in the absorption bands and the dye-molecular aggregations; and (v) the reversible cycles of spectral switching are moder- ately stable. IR Spectra Characteristics of Azo LB Films Fig. 9(a) shows an IR transmission spectrum of the nine- monolayer azo V LB film.Bands from CH, antisymmetric and symmetric stretching of the hydrocarbon chain are observed at 2918 and 2848 cm-', respectively. A medium band at 2953 cm-' is due to CH3 asymmetric stretching. Bands due to +N=C stretching of the benzothiazolium ring are identified near 1614 cm-1.16*17 Bands due to ring stretching of the naphthyl group are observed at 1587 and 1535cm-' (v19 mode like).16 A medium feature at ca. 1470cm-' can be assigned to CH, scissoring of the alkyl A band at 1392 cm -',assigned to ring stretching, is also characteristic of the naphthalene ring.21,22 It is well known that azobenzene derivatives give a band due to =N-Ph stretching in the the band 1150- 1 160 cm -' regi~n,~',~~,~~ at ca. 1157 cm -probably arises from =N-Ar stretching, and there can be little doubt that bands in the 890-830cm-' region are due to CH out-of-plane deformation of the aromatic Fig.9(b) shows an IR RA spectrum of the nine-layer LB film of azo V. Note that the relative intensities of the bands in Fig. 9(b) are fairly different from those in Fig. 9(a). Comparison of band intensities in the IR transmission and RA spectra of the nine-monolayer LB films enables discussion of the molecular orientation of the hydrocarbon chain and the chromophore of azo V, owing to the surface selection rule in IR RA spectros~opy.~~~~~The vibrational modes of the transition moments perpendicular to the surface are enhanced in an RA spectrum, whereas those with the transition moments parallel to the surface give strong bands in a transmission spectrum.The intensities of the bands from CH, antisym- metric and symmetric stretching of the hydrocarbon chain, which have transition moments perpendicular to the molecular axis, are much stronger in the RA spectrum than in the transmission spectrum. For the IR transmission measurement nine monolayers of azo V were deposited on both sides of a CaF, plate whereas for the RA measurement they were deposited on only one side of an Au-evaporated glass slide, and therefore, the ordinate scale of the RA spectrum [Fig. 9(b)] was doubled compared with those of the trans- 30 ) and 563 nm (O), I I 1200 800 I I I 1 3200 2800 2400 2000 1600 wavenum ber/cm-' Fig.9 (a) IR transmission spectrum of a nine-monolayer LB film of azo V, (b) IR RA spectrum of a nine-monolayer LB film of azo V and (c) IR transmission spectrum of azo V in the solid state.For the 1R transmission measurement nine layers of azo \i' were deposited on both sides of the CaF, substrate, whereas for RA measurements they were deposited on only one side of an Au-evaporated glass slide. J. MATER. CHEM., 1994, VOL. 4 mission spectrum. The result for azo V films indicates the hydrocarbon chain is tilted considerably with respect to the surface normal. The bands due to the in-plane vibrational modes of the chromphoric part also gain in intensity in the RA spectrum; particularly striking is that the band at 1587 cm-I due to stretching of the naphthyl group becomes stronger in the RA spectrum.However, the intensity enhance- ments of the bands from the chromophoric part are not seen in the RA spectrum of the azo V film, except for the band at 1587 cm-'. It seems, therefore, that the chromophoric part is neither perpendicular nor parallel to the substrate surface, being tilted with respect to the surface normal. The azo V molecule is probably twisted in the C-N=N and/or N=N-C single bonds. Since a band due to N=N stretching can not be established in the IR transmission and RA spectra, it is difficult to discuss the orientation of the N=N bond. However, in a resonance Raman spectrum of the LB film, an N=N stretching band is observed near 1464 ~m-',~' showing that azo V in the LB films has a trans conformation around the N=N bond similar to that reported for azo I1 in pre- vious paper." Fig.9(c) shows an IR transmission spectrum of azo V in the solid state obtained by using a microspectroscopic tech- nique. The marked spectral changes in the IR spectra between the LB films and the solid state of azo V was observed. In the spectrum of the solid state, a moderate band at ca. 1099 cm-' is ascribed to C104-,31 although this was lost during the formation of the LB films. In particular, four bands at 1603,1392,1296 and 1163 cm-I are very intense in the spectrum of the solid state whereas they are very weak in both the transmission and the RA spectra of the LB films. On the other hand, the bands at 1587 and 1570cm-I are strong to medium in the LB film spectra and very weak or almost missing in the solid-state spectrum.Thus, the spectra of the LB films are different from those of the solid state. The IR spectral changes observed in the LB film might be based on the formation of an H-aggregate, characteristic of the LB film. Fig. 10 shows the IR transmission spectral changes for the nine-monolayer LB film of azo V when subjected to cyclic AT and HT. First, the transmission spectrum of an as-deposited film was recorded [Fig. lO(u); H-like aggregate], and then AT for 30s was carried out and the subsequent spectrum obtained [Fig. 10(b)]. The latter spectrum is different from the original [Fig. lO(a)], but was similar to that of the solid state [Fig.9(c)]. It seems that the spectrum in Fig. 10(b) might be due to the (M) state of azo V in the film. The film was then kept for 15min in a thermostatically controlled environment at 90°C. After cooling to 30°C the spectrum was again measured [Fig. lO(c)]. This is also different from that shown in Fig. 1O(a) and (b),and shows two split bands at 1556-1583cm-' and a strong to medium band at 1157 cm-'. The relative intensity (compared with the CH, antisymmetric band at ca. 2920cm-') of the latter band is larger than that in Fig. lO(a), but is moderately small com- pared with that for the monomer [Fig. 10(b)]. The observed spectral changes [Fig. lO(c)] might be due to the formation of an H*-like aggregate characteristic of the azo V LB film.As can be seen in Fig. 10(d), after AT of the H*-like aggregate state the IR spectrum almost completely returns to the spectrum shown in Fig. 10(b). The spectra in Fig. 10(b) and (d) are almostly identical (see, for example, the frequencies and bandwidths of the CH, stretching bands and the spectral features in the 1598-1100 cm-I region). The repeating cycle of HT and AT resulted in the spectra shown in Fig. 10(d) and (e).Thus, in subsequent experiments, the spectra after the first AT and HT are almost reproduced by the second AT and HT. Furthermore, an important change between the spectrum I 1 -3000 2000 lob0 waven urnber/crn-' Fig. 10 IR transmission spectral changes for the nine-monolayer LB films of azo V subjected to the repeating AT and HT cycle). (a) As-deposited film; (b) after AT; (c) after AT--+HT; (dl after ATtHTtAT; and (e)after ATtHT-tAT-tHT.of an as-deposited azo V film and those of the films after AT and/or HT is the shape of a band near 1470 cm-' assignable to CH, scissoring; the band appears as a doublet in the spectra of the as-deposited film and HT film [Fig. lo@), (c) and (e)] whereas it appears as a singlet in the LB filni after AT [Fig. 10(b) and (d)]. It is well known that the band from CH, scissoring of the hydrocarbon chain is sensitive to the intermolecular interaction and its singlet appearance is characteristic of n-alkanes with a hexagonal sub-cell packing, whereas its splitting is indicative of an orthorhombic sub-cell pa~king.'~.~~Therefore, the appearance of the doublet (at ca.1468-1475 cm-') in the as-deposited film spectrum [Fig. lO(a)] suggests that the alkyl chain is in an orthorhomic sub-cell packing in the azo V film. In contrast to the spectrum 1200 in Fig. lO(a), it seems that the one for azo V in the LB film after AT crystallizes with a hexagonal sub-cell packing, because its CH, scissoring band appears as a singlet band [Fig. 10(b) and (d)]. Also, the bands from CH2 scissoring [seen in Fig. 1O(c) and (e)] in the 1459-1475 cm-' region resemble each other in shape. Aspects of these systems can be classified by a type of H*-like aggregate state, and differ from that in the spectrum in Fig. 10(a) of the as-deposited film (H-like aggregate state).The IR spectroscopic behaviours for azo VI LB films are very similar to those of azo V, except for the relative intensitives of some bands. The last observation is in good agreement with those for the visible absorption spectra (Figs. 4 and 5). These results suggest that HC1 vapour might cause some change that is not based on an addition of HC1 to the dye molecule in the LB film. Thus, it seems that these changes are caused by the rearrangements of the dye molecules between the available forms of association, such as the M state and aggregate states and these phenomena after cyclical treatments can be regarded as a memory effect of the chromophore orientation in LB films. Conclusion The present study has demonstrated the effects of heat, acidic- and basic-vapour phase treatments on thin films of heteroaryl- azo dyes.The compounds used tend to form aggregates in a manner rather different from those in other conventional azobenzene-containing amphiphilic compound^.^,' The visible absorption spectra in the solution and in the LB films comprise a monomer band or H- and H*-like aggregate bands. The molecular aggregation and the orientation in the LB films were also supported from the results of the IR transmission and RA spectra. The results obtained suggest that the heat and the vapour treatments will serve as a useful tool to enhance the required characteristic in the aggregate structure formed in the LB films after deposition. For the molecular design of functional LB films this sort of study may provide useful information. We thank Professor Y.Ozaki and S. Enomoto (student) of Kawnsei Gakuin University for their assistance in using the FTIR instrument and helpful discussion. References 1 U. Lehmann, Thin Solid Films, 1988, 160,257. 2 H. Kuhn, Thin Solid Films, 1983,99, 1. J. MATER. CHEM., 1994, VOL. 4 3 V. Czikkely, H. D. Forsterling and H. Kuhn, Chem. Phys. Lett., 1970,6,207. 4 E. S. Emerson, M. A. Conlin, A. E. Rosenoffi, K. S. Norland, H. Rodriguez, D. Chin and G. R. Bird, J. Phys. Chem., 1967, 71,2396. 5 M. Sugi, M. Saito, T. Fukui and S. Iizima, Thin Solid Films, 1985, 129, 15. 6 S. Igazeki, M. Takeda, Y. Tomioka, A. Kakuta, A. Mukoh and T. Narahara, Thin Solid Films, 1985, 134,27.7 G. Decher and B. Tieke, Thin Solid Films, 1988, 160,407. 8 C. McArdle, H. Blair and A. Ruaudel-Teixier, Thin Solid Films, 1983,99, 181. 9 E. Ando, J. Miyazaki and K. Morimoto, Thin Solid Films, 1985, 133, 21. 10 S. Xiao, Z. Lu, Y. Miao, Z. Liu, R. Zhu and Y. Wei, Thin Solid Films, 1992,210/211,784. 11 M. Shimomura, R. Ando and T. Kunitake, Brr. Bunsenges. Phys. Chem., 1983,87,1134. 12 M. Shimomura and T. Kunitake, J. Am. Chem. Soc., 1987, 109, 5175. 13 T. Seki and K. Ichimura, Thin Solid Films, 1989, 179, 77. 14 J. Heesemann, J. Am. Chem. Soc., 1980,102,2167. 15 N. Kuramoto, Dyes Pigm., 1993,21,159. 16 Raman Spectroscopy, ed., H. Hamaguchi and H. Hirakawa, Japan Scientific Societies Press, Tokyo, 1988 p. 237, (in Japanese). 17 N.Katayama, Y. Ozaki and N. Kuramoto, Chem. Phys. Lett., 1991,179,227. 18 M. Tasumi, T. Shimanouchi and T. Miyazawa, J.Mol. Spectrosc., 1962,9, 261. 19 R. G. Snyder and J. H. Schachtschneider, Spectrochim. Acta, 1963, 19, 85. 20 Y. Koyama, M. Yanagishita, S. Toda and T. Matsuo, J. Colloid Interface Sci., 1977,61,438. 21 N. B. Colthup, L. H. Daly and S. E. Wiberley, Introduction to Infrared and Raman Spectroscopy, Academic Press, San Diego, CA, 3rd edn., 1990. 22 D. Lim-Vien, N. B. Colthup, W. G. Fately and J. G. Grasselli, The Handbook of Infrared and Raman Characteristic Frequencies of Organic Molecules, Academic Press, San Diego, CA, 1991. 23 K. Kumar and P. B. Carey, Can. J. Chem., 1977,55,1444. 24 T. Takenaka and T. Nakanaga, J. Phys. Chem , 1976,80,475. 25 G. Varsanyi, Vibrational Spectra of Benzene Drriuatives, Academic Press New York, 1969. 26 N. B. Colthup, L. H. Daly and S. E. Wiberley, Introduction to Infrared and Raman Spectroscopy, Academic Press, New York, 2nd edn., 1975, p. 257 and 331. 27 R. G. Greenier, J. Chem. Phys., 1966,44, 310. 28 P-A. Chollet, J. Messier and C. Rosilio, J. Chem. Phys., 1976, 64, 1042. 29 J. Umemura, T. Kamata, T. Kawai and T. Takenaka, J. Phys. Chem., 1990,94,62. 30 S. Enomoto, Y. Ozaki and N. Kuramoto, unpublished data. 31 K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, Wiley, New York, 4th edn., 1986,p. 251. 32 R. G. Snyder, J. Mol. Spectrosc., 1961,7, 116. Paper 4/00881B; Received 14th February, 1994

ISSN:0959-9428    

DOI:10.1039/JM9940401195

出版商:RSC    

年代:1994

数据来源: RSC