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J. MATER. CHEM., 1991, 1(6), 1007-1014 Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization Part 15.t -Molecular Design of Re-entrant Nematic Mesophases in Binary Copolymers of 4'-(w-Vi n yloxyal koxy) biphenyl-4-yl Cyan ides Virgil Percec* and Myongsoo Lee Department of Macromolecular Science, Case Western Reserve Universitx Cleveland, OH 44 106, USA The first examples of homopolymers and copolymers of 4'-(o-vinyloxyalkoxy)biphenyl-4-yl cyanides which exhibit the l-N--SA,,-N,, sequence of phase transitions have been described. All previously reported polymers exhibiting an N,, phase were based on a polyacrylate backbone. Poly~1-[5-(4'-cyanobiphenyl-4-yloxy)pentyloxy]ethylene~ [i.e. poly(6-5), where 5 represents the number of methylenic units in the spacer] displays an N,, phase over a large range of degrees of polymerization (DP= 10-30).Systematic binary copolymerization experiments have demonstrated that N,, mesophases are exhibited by copolymers generated from structural units, one of which belongs to a homopolymer leading to an SA phase, and the other to N or glassy phases. The following copolymer compositions were shown to display the I-N-SAd-N,, sequence: pol y( 1-[11-(4'-cyanobiphenyl-4-yloxy)undecanyl-oxy]ethylene-co-l-[5-(4'-cyanobiphenyl-4-yloxy)pentyloxy]ethylene}X/Y (poly[(6-ll)-co-(6-5)]X/Y), where X/Y rep-resents the molar ratio of the two structural units i.e., poly[(6-ll)-c(~(6-5)]1/9(DP=20),poly[(6-11)-co-(6-3)]3/7 (DP=20),POIY[ (6-8)-~*( 6-2)]6/4 (DP= 10), POIY[ (6-1 1)-~0-(6-2)]4/6(DP= 15).Keywords: Vinyl ether; Re-entrant nematic mesophase; Liquid crystal; Living cationic polymerization The re-entrant nematic phase (N,,) was discovered in 1975 in the following phases: glassy-SA,'2"*b SA-SA,12' N-N,12' and low molar mass liquid crystals.' Since then it has received SA-N.12c substantial theoretical and experimental interest.2 The first The first goal of this paper is to describe the synthesis and side-chain liquid-crystalline polymer exhibiting an N,, phase characterization of poly{1-[1 1 -(4-cyanobiphenyl-4-yloxy) was reported in 1986.394 This polymer was based on a undecanyloxy] ethylene-co- 1-[5-(4-cyanobiphenyl-4-yloxy) polyacrylate backbone, six methylenic units in the flexible pentyloxy]ethylene}X/Y {poly[(6-11)-~0-(6-5)]X/Y>,where X/Y spacer, and 4-cyano-4'-oxybiphenyl side groups.In the mean- represents the molar ratio of the two structural units, with time, several other polyacrylates containing mesogenic units DP of ca. 20. Poly(6-11) with a DP of ca. 20 exhibits in the with cyano groups and spacer lengths with five or six atoms second heating scan enantiotripic SA and Sx phases,'le poly(6- were reported to exhibit the unusual I-N--SAd-N,, 5) with the same degree of polymerization exhibits enanti- So far, there are two copolymerization experi- otropic N and SA phases.'lb A reinvestigation of the phase ments with a monomer whose polymer exhibits an N,, phase behaviour of poly(6-5) with different molecular weights will and a monomer whose polymer exhibits an N or SA meso-demonstrate that it displays the I-N-SAd-N,, sequence. The phase." Both have demonstrated that the copolymer tendency second goal of this paper is to demonstrate that all copolymers to generate an N,, phase decreases with the increase of the derived from monomer pairs whose parent homopolymers content of the structural units derived from the latest two exhibit dissimilar phases, one of them being an SA phase, the monomers.Nevertheless, copolymerization of a monomer other N or glassy, have the ability to generate, at a certain which generates a polymer with an N phase with a monomer copolymer composition, an N,, mesophase. which produces a polymer exhibiting an SA phase leads to copolymers which display an N,, phase over a certain range of composition.lo Experimental Previous publications from this series reported on the Materialssynthesis of 4'-(co-vinyloxyalkoxy)biphenyl-4-ylcyanides con- taining ethyl, propyl and butyl,"" pentylllb hexyl,"' heptyl,'lb All materials were available commercially and were used octyl,' lC,nonyl,"d decanyl'ld and undecanyl"" alkyl groups, as received or purified as described previously. "7" Methyl their living cationic polymerization, and the characterization sulphide (anhydrous, 99%, Aldrich) was refluxed over 9-bora- of the resulting polymers as a function of molecular weight. bicycloC3.3. llnonane (9-BBN, crystalline, 98%, Aldrich) and In addition, the synthesis and characterization of binary then distilled under argon.Dichloromethane (99.6%, Aldrich) copolymers of 4'-(co-vinyloxyalkoxy)biphenyl-4-yl cyanides used as a polymerization solvent was first washed with with constant degrees of polymerization, narrow molecular concentrated sulphuric acid, then with water, dried over weight distributions and variable composition was investi- anhydrous magnesium sulphate, refluxed over calcium hydride gated for the pairs of monomers based on the following alkyl and freshly drilled under argon before each use. Trifluoro- groups: ethyl-~ctyl,'~" undecanyl-ethyl,'2b undecanyl-hex-methane sulphonic acid (triflic acid, 98%, Aldrich) was distilled yl, 12' pentyl-propyl,12' and undecanyl-propyl. 12' These under argon. copolymers were generated from monomer pairs whose parent homopolymers exhibit as the highest temperature mesophase Techniques 'H NMR (200 MHz) spectra were recorded on a Varian XL-t Part 14.V. Percec and M. Lee, Macromolecules, in the press. 200 spectrometer. TMS was used as internal standard. A 1008 J. MATER. CHEM., 1991, VOL. 1 120 Perkin-Elmer DSC-4 differential scanning calorimeter, ]@) A-A-A-equipped with a TADS 3600 data station was used to deter-mine the thermal transitions which were reported as the maxima and minima of their endothermic and exothermic 0' 8oi A-A-A-0p 60 A'A' NrfJ 01 I I I I I I 0 5 10 15 20 25 30 35 DP 120 100-80 -0 60-40-20 -0. glassy 0 5 10 15 20 25 30 35 DP Fig. 1 The dependence of phase-transition temperatures of poly(6-5) us.degree of polymerization. (a) Data from heating scans: 0,Tg;A, T(N~~-s~~); a,T(N-I). (b) Data from cooling scans: 0,T(s~~--N); 0,Tg;a,T(sAd-Nre); m, T(N-s.4,); A, T(1-N) peaks, respectively. In all cases, heating and cooling rates were 20 "C min- unless otherwise specified. Glass-transition temperatures (T,) were read at the middle of the change in the heat capacity. For certain polymer samples, the first heating scans sometimes differ from the second and subsequent heating scans, which will be discussed later. However, the second and subsequent heating scans are identical. The first heating scans can be re-obtained after proper thermal treat- ment of the polymer sample. Both the first and the second DSC heating scans will be reported and discussed.A Carl-Zeiss optical polarized microscope (magnification: 100 x) equipped with a Mettler FP 82 hot stage and a Mettler 800 central processor was used to observe the thermal transitions and to analyse the anisotropic textures.', Relative molecular weights were determined by gel permeation chromatography (GPC) with a Perkin-Elmer series 10 LC instrument equipped with LC-100 column oven, LC-600 autosampler and a Nelson analytical 900 series integrator data station. The measure- ments were made at 40 "C using the UV detector. A set of Perkin-Elmer PL gel columns of lo4 and 500A with CHCl, as solvent (1 x lo-, dm3 min-') and a calibration plot con- structed with polystyrene standards was used to determine the molecular weights.Therefore, all molecular weights dis- cussed in this paper are relative to polystyrene. High perform- ance liquid chromatography (HPLC) experiments were performed with the same instrument. Synthesis of Monomers Monomers (6-11)'le and (6-5)'lbwere synthesized and purified as described in previous publications. Their purity was >99% (HPLC). Their detailed characterization is described in the previous publications. Table 1 Cationic copolymerization of 6-11 with 6-5 [MIo =[6-11] +[6-5]=0.256-0.326 mol dm-3; [M]o/[I]o resulting polymers" sample no. [6-11]/[6-5] (mol/mol) polymer yield (%) M,xIO-~ MJM, 1 87 2 85 3 77 4 82 5 77 6 79 7 82 8 74 9 75 10 83 11 81 5.4 1.13 5.7 1.19 5.8 1.09 6.8 1.14 6.4 1.16 6.3 1.15 6.3 1.15 6.2 1.13 6.8 1.15 7.7 1.12 8.2 1.12 DP 18 18 17 18 19 18 17 17 18 20 19 (polymerization temperature, 0 "C; polymerization solvent, methylene chloride; =20; [(CH3)2S]o/[I]o = 10; polymerization time, I h) and characterization of the phase transitions1"C and corresponding enthalpy changes/kJ mol -heating g 29.1 N,, 69b SA 102.3 (-) N113.2 (0.59) I g 28.5 N,, 69b SA 102.1 (-) sA113.5 (0.54) I g 25.4 N,, 40.3b S, 114.5 (-) N118.2 (0.88) I g 25.2 N,, 40.3b S, 114.7 (-) N118.4 (0.92) I g 22.7 SA 123.2 (1.17) I g 20.4 S, 122.7 (1.13) I g 18.4 S, 130.8 (1.67) I g 17.7 SA 130.6 (1.55) I g 16.2 s, 134.0 (2.10) I g 15.3 S, 133.7 (2.34) I g 15.4 SA 139.1 (2.34) I g 14.7 SA 138.5 (2.34) I g 15.2 S, 143.1 (2.59) I g 15.7 S, 143.5 (2.67) I g 14.3 SA 148.6 (2.93) 1 g 13.5 SA 148.1 (2.85) I g 13.9 SA 149.8 (3.31) I g 12.7 SA 149.0 (3.22) I g 13.8 K 53.6 (11.01) 3,153.9 (3.65) I g 12.5 SA 153.6 (3.56) I g 14.5 K 57.1 (14.40) S,157.2 (3.77) I g 14.0 Sx 44.2 (3.89) SA156.4 (3.64) I cooling I 108.9 (0.50) N 90.3 (-) SA69b N,, 25.5 g I 1 15.0 (0.84) N 109.4 (-) SA40.3b N,, 20.1 g I 117.9 (1.13) S, 15.2 g I 124.7 (1.59) SA 12.8 g I 127.4 (1.88) S, 10.3 g I 134.4 (2.30) SA 9.7 g I 1138.1 (2.51) S, 9.0 g I 1422 (2.80) S, 9.2 g I 144.0 (3.22) SA 9.0 g I 148.3 (3.35) SA 9.0 g I 149.4 (3.89) SA 18.9(2.63) Sx 8.8 g Data on first line are from first heating and cooling scans; data on second line are from second heating scan.* Data obtained from optical polarized microscopy. J. MATER. CHEM., 1991, VOL. 1 CH,=CH CH2=CH H (CH2CH) x (CH2CH)y OCH3 I I I I X 0 +Y 0 0 0I I (9 I I (CH2)11 (CH2)S (ii) * (CH2111 (CH2)SI I I I0 0 0 0 NC NC NC Nk Scheme 1 Copolymerization of 6-11 with 6-5. (i) CF,SO,H, (CH,)*S, CH,Cl,; (ii) CH,OH, NH,OH Cationic Polymerizations and Copolymerization Polymerizations were carried out in glass flasks equipped with Teflon stopcocks and rubber septa under argon atmos- phere at 0 "C for 1 h. All glassware was dried overnight at 130 "C. The monomer was further dried under vacuum over- night in the polymerization flask. Then the flask was filled with argon, cooled to 0 "C and the methylene chloride, dimethyl sulphide and triflic acid were added via a syringe.The monomer concentration was ca. 10 wt.% of the solvent volume and the dimethyl sulphide concentration was x10 greater than that of the initiator. The polymer molecular weight was controlled by the monomer: initiator ([MIo :[IlO) ratio. After the polymerization had been quenched with ammoniacal methanol, the reaction mixture was precipitated into methanol. When necessary, the polymers were reprecipi- tated until their GPC and HPLC traces showed complete absence of unreacted monomers. Although polymer yields are 0110 /-/ yl-SA 1/9 t D Q) 1009 lower than expected owing to losses during the purification process, conversions determined by HPLC and GPC analysis before polymer purification were almost quantitative in all cases.Results and Discussion The first examples of mesogenic vinyl ethers and liquid- crystalline poly(viny1 ether)s were reported from our labora- tory.14 Since then several research groups became actively engaged in the synthesis of liquid-crystalline poly(viny1 ether)s mainly because they can be polymerized by a living cationic mechanism. 119 12915-1 8 Our preferred initiating system is CF3S03H-S(CH3)* since it can be used to perform living cationic polymerizations in CHzC12 at 0 "C, and therefore, allows the preparation of polymers with narrow molecular weight distribution and controllable molecular weight." In addition, we have shown that this system can be used to initiate the living cationic polymerization and cyclopolymeriz- ation of mesogenic vinyl ethers containing a variety of func- tional groups. 11*12~18 We will first re-investigate the phase behaviour of poly(6- 5) as a function of molecular weight.Previously, by using a combination of techniques based on DSC and thermal optical polarized microscopy,"* we concluded that poly(6-5) exhibits enantiotropic N and SAmesophases. An N,, phase is expected below the S, phase of these polymers owing to the ability of liquid-crystalline compounds containing mesogens with cyano groups to generate an SAd phase below the high-temperature N phase.'c.2d Therefore, although we do not have yet definitive evidence from X-ray diffraction experiments, we will assume that the SA phase from above the N,, phase is an SAd phase.Fig. l(a), (b) presents the re-evaluated phase diagrams of poly(6-5) as a function of molecular weight. Since the transition from the SAdto N,, and N,, to SAd does not display a first- order transition on the DSC curve, this transition was deter- 515 SAt \-0 \-a, 614 \I I K/01011 -10 30 70 110 150 190 -10 30 70 110 150 190 -10 30 70 110 150 190 7°C T/"C TI "C Fig. 2 DSC traces displayed during the first heating (a),second heating (b) and first cooling (c) scans by poly(6-11), poly(6-5) and poly[(bll)- CO-(6-5)]X/Y J. MATER. CHEM., 1991, VOL. 1 140 120 0 i=- SA 80 SA 40 0 SX 0 I glassy I I I I 20 01 000000 glassy I I I 000 I I 0.0 0.2 0.4 0.6 0.8 1.0 Fi-11 160 (c1 200 (d1 140- N l8OI 9i=- 80- SA sx 0 loo?8ol60 0 0.0 ~ ~glassy I I 0.2 0.4 ~ o I 0.6 o I 0.8 a I 1.0 o o o 40 f 0.0 I 0.2 I 0.4 I 0.6 I 0.8 I 1.0 c F6-1 1 p6-1 1 I R0 3.0- 7 2.5- - 7 2.0-P E z 0 1.5- 6 0.5 0.0;0.0 I 0.2 I 0.4 I 0.6 I 0.8 I 1.0 F6-11 Fig.3 The dependence of phase-transition temperatures on composition (Fs-ll =mol fraction of 6-11) of poly[(6-11)-~0-(6-5)]X/Y.(a) Data from first heating scan: 0, T,; U, T(K-SA); 0,T(SA-I) or T(SA-N); A, T(N-I); A, T(Nre--sAd).(b) Data from second heating scan: same symbols except, 0, T(S,-S,). (c) Data from first cooling scan: 0, T,; A, T(1-N); a, T(I-SA) or T(N-SA); A, T(SAd-Nre);+, T(SA-S,). (d) The dependence of SA-N and SA-I phase-transition temperatures on composition of poly[(bl l)-c0-(6-5)]X/Y: m, data calculated by Schroeder- van Laar equation; IJ, experimental data from the first heating scan.(e) The dependence of the enthalpy changes associated with the mesomorphic-isotropic and isotropic-mesomorphic phase transitions: 0,AH(N-I) (data from the first heating scan); A,AH(N-I) (data from the second heating scan); 0,AH(1-N) (data from the first cooling scan) us. copolymer composition J. MATER. CHEM., 1991, VOL. 1 i2 80 SA0 "i"' AoA 0 Nre 0 0 Nre400 SX0:1 SA 2 sxOO 00 00glassy glassy O! I I I I I' I I I I I 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 Fi-11 F6-11 Fig.4 The dependence of phase-transition temperatures on composition of poly[(6-11)-~0-(6-3)]X/Y with degree of polymerization 20. (a) Data from the second heating scan: 0, Tg;A, T(N-I); 0,T(SA-I) or T(SA-N); A, T(Nre-sAd);0, T(S,-SA). (b)Data from the first cooling scan: *,Tg;A, T(1-N); 1,T(I-SA) Or T(N-SAd); A,T(SAd-Nre); e, T(s~-s,) mined by optical polarized microscopy. Representative optical polarized micrographs of the texture exhibited by the high- temperature nematic, SAd and N,, phases of poly(6-5) with DP =30 are presented in Plate 1. Table 1 summarizes the results of the copolymerization of 6-11 with 6-5. Attempts were made to prepare copolymers with DP=20. As discussed in a previous paper from this series,I2 these copolymerization experiments follow an azeo- tropic model (rl =r2= 1) and therefore, the composition of copolymers is equal to that of the monomer feed.This copolymerization experiment is outlined in Scheme 1. Fig. 2(a)presents the DSC traces of polyC(6-1 l)-co-(6-5)]X/ Y copolymers obtained from the first heating scan. The DSC traces obtained from the second and subsequent heating scans are given in Fig. 2(b), and those obtained from the cooling scans in Fig. 2(c). Second and subsequent heating scans display identical DSC traces. Only poly [(6-1l)-co-(6-5)]X/Y with X/ Y =9/1 and 10/0 exhibit first DSC scans which differ from those of the second heating scans. All cooling scans of these copolymers are identical. In the first and subsequent heating 0 0 Nre 40 0 OO '"1 0 glassy scans, poly(6-5) exhibits enantiotropic N and SAdmesophases [Fig. 2(4, (b)].In the first DSC heating scan, poly[(6-ll)-co- (6-5)]X/Y with X/Y =9/1 and lO/O exhibit crystalline melting followed by an enantiotropic SA mesophase [Fig.2(a)]. In the second heating scan, poly(6-11) exhibits enantiotropic SA and Sx mesophases, while poly[(6-11)-~0-(6-5)]X/Y with X/Y =9/1 only an enantiotropic SA mesophase [Fig. 2(b)]. This behav- iour is due to the slow crystallization process induced by the close proximity of the crystallization-transition temperature to the glass-transition temperature. All copolymers with X/ Y =10/0-2/8 display an enantiotropic SA mesophase. The copolymer with X/Y = 1/9 and poly(6-5) exhibit enantiotropic N and SA phases [Fig.2(a)-(c)]. The inspection of poly(6-5) and poly[(6-11)-~0-(6-5)] 1/9 on the optical polarized microscope reveals N,, mesophases (Plate2). Therefore, the SA phase of these two polymers is probably an SAd phase. The dependences of phase-transition temperatures of polyC(6-1 l)-co-(6-5)]X/Y on composition as determined from first heating, second heating, and cooling scans are plotted in Fig. 3(4-(c). All phase transitions show glassy .... O! I I I I I I 0.0 0.2 0.4 0.6 0.8 1.0 b:O 0:2 0:4 0:s 0:8 1:0 F6-8 F6-8 Fig. 5 The dependence of phase-transition temperatures on composition of poly[(6-8)-co-(6-2)]X/Y with degree of polymerization of 10. (a)Data from the second heating scan: 0,Tg;A, T(N-I); 0,T(SA-I); A, T(Nre-sAd).(b)Data from the first cooling scan: 0, Tg;A, T(1-N);.,iV-SA); A,T(SAd-Nre) J.MATER. CHEM., 1991, VOL. 1 160 16* I(b) 140 140 1 20 100 -Ix N'P 80 SA SA i=-N NA60 0 Nr, a glassy ooooo 1 2olI I I I I 1 01 I I I I I 0.0 0.2 0.4 -0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 F6-11 FS-11 Fig. 6 The dependence of phase-transition temperatures on composition of poly[(bll)-c0-(6-2)]X/Y with degree of polymerization 15. (a) Data from the second heating scan: 0, T6;A, T(N-I); 0,T(SA-I) or T(SA-N); A, T(Nre-sAd);0, T(Sx-S,). (b) Data from the first cooling scan: 0,T6;A,T(1-N); .,T(I-SA) Or T(N-SAd); A, T(sAd-Nre);+, T(s~-sx) continuous dependences of copolymer composition. PolyC(6-eder-van Laar equations,20.21and agree qualitatively with 1l)-cu-(6-5)]2/8 exhibits a triple point on its phase behaviour the calculated ones.Fig. 3(e) presents the experimental and [Fig. 3(a),(b)].The upward curvature of the SA-I, SA-N and calculated data for the SA-N and SA-I transition temperatures of the entire transition temperature dependences us. copolymer of poly[(6-1l)-c0-(6-5)]X/Y copolymers. Thus, the phase dia-composition [Fig. 3(a)-(c)] can be explained by the Schro-gram of these copolymers can be regarded as close to that Fig. 7 Representative optical polarized micrographs (100 x) of the phases exhibited by poly[(6-8)-~0-(6-2)]6/4with degree of polymerization of 20. (a) N phase at 100 "C; (b) transition from N to SAd at 92.8 "C;(c) SAd phase at 85.8 "C; (d) N,, phase at 50 "C J.MATER. CHEM., 1991, VOL. 1 Plate 1 Representative optical polarized micrographs (100x) of the phases exhibited by poly(6-5) with degree of polymerization of 30: (a)high-temperature N phase at 109.2 "C;(b)transition from N to SAdphase at 102.4 "C; (c)SAdphase 89.7 "C; (d) N,, phase at 54.2 "C V. Percec and M. Lee (Facing p. 1012) Plate 2 Representative optical polarized micrographs (100x) of the phases exhibited by poly[(6-ll)-c0-(6-5)19/1:(a)N phase at I 13 'C; (h)S,, phase at 92 "C; (c) N,, phase at 36 "C J. MATER. CHEM., 1991, VOL. 1 (a) Fig. 8 Representative optical polarized micrographs (100 x) of the phases exhibited by poly[(6-1l)-c0-(6-2)]4/6 with degree of polymerization of 20.(a)N phase at 103.6 "C; (b)transition from N to SAd at 98 "C; (c) SAd phase at 83 "C;(d) transition from SAdto N,, at 65.4 "C;(e) N,, phase at 55 "C expected for an ideal solution resulting from the structural units of the copolymer. The enthalpy changes associated with the SA-I, SA-N and of the reversed phase transitions deter- mined from the first and second heating, and first cooling DSC scans (Table 1) are plotted as a function of copolymer composition in Fig. 3(d).This dependence is linear. Therefore, it demonstrates a weight average dependence of copolymer composition. The phase behaviour of poly{ 1 -[11-(4'-cyanobiphenyl- 4-yloxy)undecanyloxy]ethylene-co-1-[3-(4-cyanobiphenyl-4-yl-oxy)propoxy]ethylene}X/Y{poly[(6-1 l)-c0-(6-3)]X/Y} with DP =ca.20 and molecular weight distributions of ca. I. 1 was investigated previously.12' We will discuss here only the phase behaviour of this copolymer as obtained from second and subsequent heating and from first and subsequent cooling scans. Second and subsequent heating scans are identical. All cooling scans are also identical. Fig. 4(a) presents the phase behaviour of this copolymer determined from the second heating scan, while Fig. 4(b) shows the phase behaviour obtained from the first cooling scan. Poly(6-3) displays an enantiotropic N mesophase, while poly(6-11) has enantiotropic SA and Sxmesophases. The isotropization transition tempera- ture displays a continuous dependence of copolymer compo- sition with a triple point for poly[(6-11)-~0-(6-3)14/6.PolyC(6-11)-co-(6-3)]3/7 exhibits the I-N-SAd-Nresequence [Fig.qa), (b)]. Copolymers with X/Y =4/6-0/10 display an N phase while copolymers with X/Y =4/6-10/0 exhibit an SA phase. Plate 3 presents representative optical polarized micrographs exhibited by the N, SAd and N,, phases of poly[(6-11)-~0-(6- 3113/7.The phase behaviour of poly{ 1 -[8-(4'-cyanobiphenyl- 4-yloxy)octyloxy]ethylene-co-1-[2-(4'-cyanobiphenyl-4-yloxy)-ethoxy]ethylene}X/Y{ poly[(6-8)-~0-(6-2)]) with DP x 10 and of poly{ 1-[11-(4'-cyanobiphenyl-4-yloxy)undecanyloxy]-ethylene-co-1-[2-(4'-cyanobiphenyl-4-yloxy)ethoxy] ethylene) X/Y{poly[(6-11)-co-(6-2)]} with DP x 1512b is similar. Both copolymers are based on a monomer which upon polymeriz- ation gives a glassy homopolymer, i.e.poly(6-2),"" and a monomer which upon homopolymerization leads to a polymer J. MATER. CHEM., 1991, VOL. 1 ation of all phases by X-ray scattering experiments. These results will be reproted in an independent publication. Financial support from the Office of Naval Research is gratefully acknowledged. We thank Dr. G. Sigaud of Bordeaux Liquid Crystal Group for suggesting the presence of an N,, phase in poly(6-5) and for many helpful discussions. References 1 (a) P. E. Cladis, Phys. R$v. Lett., 1975, 35, 48; (b) P. E. Cladis, R.K. Bogardus, W. B. Daniels and G.N. Taylor, Phys. Rev. Lett., 1977, 39, 720; (c)D. Guillon, P. E. Cladis and J. Stamatoff, Phys. Rev.Lett., 1978, 41, 1598; (d) P. E. Cladis, R. K. Bogardus and D. Aadsen, Phys. Rev. Ser. A., 1978, 18,2292; (e)N. H. Tinh, J. Chim. Phys., 1983, 80, 83; (f)J. W. Goodby, T. M. Leslie, P. E. Cladis and P. L. Finn, in Liquid Crystals and Ordered Fluids, ed. A. C. Griffin and J. F. Johnson, Plenum, New York, 1984, p. 203. 2 See e.g. (a) G. Sigaud, N. H. Tinh, F. Hardouin and H. Gasparoux, Mol. Cryst. Liq. Cryst., 1981, 69, 81; (b)displaying an enantiotropic SA mesophase, i.e. ~oly(6-8)~'~ and poly(6-11)"". The phase behaviour of these two copoly- mers obtained from second heating and first cooling scans is presented in Fig. 5 and 6. Depending on composition, these copolymers exhibit either enantiotropic SA or N mesophases. In both cases the copolymers with <20% structural units derived from the monomer leading to the glassy polymer, i.e.poly(6-2), are amorphous. Poly[(6-8)-co-(6-2)]7/3 and polyC(6- 1l)-co-(6-2)]5/5 exhibit a triple point on their phase behaviour. Poly[(6-8)-co-(6-2)]6/4 and polyC(6-1 l)-co-(6-2)]4/6 exhibit the I-N-sAd-Nre sequence. Fig. 7 and 8 present representative optical polarized micrographs of the textures exhibited by the N, SAd and N,, phases of poly[(6-8)-co-(6-2)]6/4 and polyC(6- 11)-~0-(6-2)]4/6. Conclusions Poly(6-5) represents the first example of a side-chain liquid- crystalline poly(viny1 ether) that exhibits the I-N-SAd-N,, sequence. Previous examples of polymers displaying an N,, phase were all based on a polyacrylate PolyC(6-ll)-~0-(6-5)] 1/9 (DP=20), p01~[(6-11)-~0-(6-3)]3/7(DP=20), p01~[(6-8)-~0-(6-2)]6/4 (DP = lo), p01~[(6-11)-~0-(6-2)]4/6 (DP= 15) also display the I-N-sAd-Nre sequence.All these copolymers present a triple point on their phase diagram. The copolymers were generated from structural units which belong to pairs of homopolymers exhibiting enantiotropic SA and Sx,and N, SAd and Nre{poly[(6-11)-~0-(6-5)X/Y), enanti-otropic SA and Sx,and N {poly[(6-11)-~0-(6-3)X/Y), enanti-otropic SAand Sx, and glassy{ polyC(6-1 l)-co-(6-2)]X/Y) phases respectively. The N,, phase is obtained in all cases for copoly- mer compositions which are located close to the triple-point composition and are richer in the structural units derived from the monomer which leads to either nematic or glassy homopolymers.These results suggest that copolymers with N,, mesophases can be obtained from any pair of 4'4~0- vinyloxyalkoxy)biphenyl-4-ylcyanides as long as one mono- mer leads to a homopolymer exhibiting an SA phase and the other to a homopolymer exhibiting either a glassy or an N phase. The most probable explanation for the formation of the N,, phase in these polymers and copolymers is similar to that provided for the other low molar mass and polymeric liquid crystals containing cyano groups and exhibiting an N,, phase, i.e. it provides a pathway to transform the SAd phase which contains dimeric and monomeric mesogens within the same layer to an SAl phase which contains only dimeric mesogens present in an interdigitated layered structure.2d The support of this explanation requires a complete characteriz- F.Hardouin, A.M. Levelut, M. F. Archard and G. Sigaud, J. Chim. Phys., 1983, 80, 53; (c)F. Hardouin, Physica A, 1986, 140, 359; (d) P. E. Cladis, Mol. Cryst. Liq. Cryst., 1988, 165, 85. 3 P. Le Barny, J. C. Dubois, C. Friedrich and C. Noel, Polym. Bull., 1986, 15, 341. 4 T. I. Gubina, S. G. Kostromin, R. V. Talroze, V. P. Shibaev and N. A. Plate, Vyskomol. Soed. Ser. B., 1986, 28, 394. 5 V. Shibaev, Mol. Cryst. Liq. Cryst., 1988, 155, 189. 6 N. Lacoudre, A. Le Borgue, N. Spassky, J. P. Vairon, P. Le Barny, J. C. Dubois, S. Esselin, C. Friedrich and C. Noel, Mol. Cryst. Liq. Cryst., 1988, 155, 113. 7 N. Spassky, N. Lacoudre, A. Le Borgue, J. P.Vairon, C. L. Jun, C. Friedrich and C. Noel, Makromol. Chem. Makromol. Symp., 1989, 24, 271. 8 T. A. Gubina, S. Kise, S. G. Kostromin, R. V. Talroze, V. P. Shibaev and N. A. Plate, Liq. Cryst., 1989, 4, 197. 9 S. G. Kostromin, V. P. Shibaev and S. Diele, Makromol. Chem., 1990, 191, 2521. 10 C. Legrand, A. Le Borgue, C. Bunel, A. Lacoudre, P. Le Barny, N. Spassky and J. P. Vairon, Makromol. Chem., 1990, 191, 2979. 11 (a) V. Percec and M. Lee, J. Macromol. Sci.: Chem., 1991, A28, 651; (b) V. Percec, M. Lee and C. Ackerman, Polymer, in the press; (c) V. Percec and M. Lee, Macromolecules, 1991, 24, 1017; (d) V. Percec and M. Lee, Macromolecules, 1991, 24, 2780; (e) V. Percec and M. Lee and H. Jonsson, J. Polym. Sci. Polym. Chem.Ed., 1991, 29, 327. 12 (a) V. Percec and M. Lee, Polymer, in the press; (b) V. Percec and M. Lee, Polym. Bull., 1991,25, 131; (c)V. Percec and M. Lee, Macromolecules, in the press. 13 (a) D. Demus and L. Richter in Texture of Liquid Crystals, Verlag Chemie, Weinheim, 1978; (b) G. W. Gray and G. W. Goodby, in Smectic Liquid Crystals. Textures and Structures, Leonard Hill, Glasgow, 1984. 14 J. M. Rodriguez-Parada and V. Percec, J. Polym. Sci., Polym. Chem. Ed., 1986, 29, 327; (b)V. Percec and D. Tomazos, Polym. Bull., 1987, 18, 239. 15 (a) T. Sagane and R. W. Lenz, Polym. J., 1988, 20, 923; (b) T. Sagane and R. W. Lenz, Polymer, 1989,30,2269; (c)T. Sagane and R. W. Lenz, Macromolecules, 1989, 22, 3763. 16 S. G. Kostromin, N. D. Cuong, E.S. Garina and V. P. Shibaev, Mol. Cryst. Liq. Cryst., 1990, 193, 177. 17 (a) V. Heroguez, A. Deffieux and M. Fontanille, Makromol. Chem., Makromol. Symp., 1990, 32, 199; (b) V. Heroguez, M. Schappacher, E. Papon and A. Deffieux, Polym. Bull., 1991, 25, 307. 18 (a) H. Jonsson, V. Percec and A. Hult, Polym. Bull., 1991, 25, 115; (b) R. Rodenhouse, V. Percec and A. E. Feiring, J. Polym. Sci., Polym. Lett., 1990,28,345;(c)R. Rodenhouse and V. Percec, Adv. Mater., 1991, 3, 101. 19 C. G. Cho, B. A. Feit and 0.W. Webster, Macromolecules, 1990, 23, 1918; (b)C. H. Lin and K. Matyjaszewsky, Polym. Prepr. Am. Chem. SOC. Div. Polym. Chem., 1990, 31(1), 599. 20 G. R. Van Hecke, J. Phys. Chem., 1979,83, 2344. 21 M. F. Achard, M. Mauzac, M. Richard, M. Sigaud and F. Hardouin, Eur. Polym. J., 1989, 25, 593. Paper 1102226A;Received 13th May, 1991 J. MATER. CHEM., 1991, VOL. 1 Plate 3 Representative optical polarized micrographs (100x) of the phases exhibited by poly[(bl l)-c0-(6-3)]3/7 with degree of polymerization of 20. (a)N phase at 99 "C;(b)transition from N to SAd at 92.5 "C; (c) SAd phase at 83.3 "C;(d) transition from SAdto N,, at 55.6 "C; (e)N,, Dhase at 52.9 "C V. Percec and M. Lee (Facingp. 1014)

ISSN:0959-9428    

DOI:10.1039/JM9910101007

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(6), 1015-1022 Molecular Engineering of Liquid-crystalline Polymers by Living Polymerization Part 16.t -Tailor-made S,* Mesophase in Copolymers of (S)-( -)-2-Methylbutyl 4'-(w-Vinyloxyalkoxy)biphenyl-4-carboxylatewith Undecanyl and Octyl Alkyl Groups Virgil Percec,* Qiang Zheng and Myongsoo Lee Department of Macromolecular Science, Case Western Reserve University, Cleveland, OH 44706, USA The synthesis and living cationic polymerization of (S)-(-)-2-methylbutyl 4'-(8-vinyloxyoctyloxy)biphenyl-4-car box y I ate (14-8) have been desc ribed. Po Iy(1-{8-[4'-(2-m et h y Ib u toxyca rbon y I)biphen y l-4-y loxylocty loxy)et hy- lene) i.e. poly(l4-8) with degree of polymerization (DP) <40 and polydispersities G1.15 was synthesized and characterized by differential scanning calorimetry (DSC) and thermal optical polarized microscopy.All polymers exhibited enantiotropic S, and S,* mesophases. Poly(14-8) with DP > 17 exhibited also an enantiotropic un-identified S, mesophase. Copolymers of 14-8 with (S)-(-)-2-methylbutyl 4'-(1l-vinyloxyundecanyloxyjbiphenyl-4-carboxylate (14-11) were synthesized to cover the entire range of composition at DP= 15. The phase behaviour of these copolymers was investigated and was demonstrated to be similar to an ideal solution derived from the structural units of poly(14-8) and poly(l4-11). This copolymerization experiment allowed the synthesis of copolymers exhibiting, depending on composition, an Sc* mesophase from below 10 "C up to 50-80 "C.Keywords: Living cationic polymerization; Chirality; Smectic C phase; Vinyl ether; Liquid crystal Since the first examples of mesogenic vinyl ethers and liquid- crystalline poly(viny1 ether)s were reported from our labora- tory,' several research groups became actively engaged in the synthesis of mesomorphic poly(viny1 ether)s mainly because they can be polymerized by a living cationic In a previous paper we reported the influence of molecular weight on the phase behaviour of poly( 1 -[w-(4'-cyanobi- phenyl-4-yloxy)alkoxy]ethylenes with alkyl groups from ethyl to undecanyl,' and of other functional mesogenic vinyl ethers.6 The first series of liquid-crystalline copolymers with constant molecular weight, narrow molecular weight distribution and various compositions were also prepared from mesogenic vinyl ether^.'^,^^*^ These experiments have demonstrated that living cationic polymerization and copolymerization of meso- genic vinyl ethers provide a quantitative approach to the molecular design of side-chain liquid-crystalline polymers exhibiting uniaxial nematic, various smecti~,~.~'-~ chiral smec- tic C (SC*),6gand re-entrant nematic7e mesophases.Liquid-crystalline polymers exhibiting chiral mesophases, i.e. cholesteric and chiral smectic C (Sc*),839 are of both theoretical and technological interest. Liquid crystals exhibit- ing chiral smectic A (S,*) mesophases were discovered only recently" and to our knowledge, polymers exhibiting S,* mesophases have not yet been reported.Side-chain liquid- crystalline polymers exhibiting Sc* mesophases were reported from several different laboratories.6g-22 However, there is very little understanding of the molecular design of side-chain liquid-crystalline polymers displaying Sc* mesophases, and of the influence of various architectural parameters of these polymers on their dynamic^.^^,^-^^ In a previous paper we have described the synthesis and living cationic polymerization of (S)-(-)-2-methylbutyl 4'-( 1 1 -vinyloxyundecanyloxy)biphenyl-4-carboxylate(14-11) and (S)-(-)-2-methylbutyl-4'-(6-vinyloxyhexyloxy)biphenyl-4-carboxy-late (14-6)? The mesomorphic behaviour of poly(l4-11) and poly(14-6) was discussed as a function of molecular weight. t Part 15. V. Percec and M.Lee, J. Muter. Chem., 1991, 1, 1007 Only poly(l4-11) exhibited an Sc* mesophase over a narrow range of temperatures. The aim of this paper is to describe the synthesis and living cationic polymerization of (S)-(-)-2-methylbutyl 4'-(8-vinyl- oxyoctyloxy)biphenyl-4-carboxylate (14-8) and the living cat- ionic copolymerization of 14-8 with 14-1 1. These experiments will provide a convenient access to the design of side-chain liquid-crystalline polymers and copolymers exhibiting an Sc* phase over a broad range of temperatures. Experimental Materials 4-Hydroxybiphenyl (97%), dimethyl sulphate (99% +), HBr (48% in H20), 8-bromooctanoic acid (97%), borane-tetra- hydrofuran complex (I .O mol dm- solution in tetrahydrofu- ran), dimethyl sulphide (anhydrous, 99% +, packaged under nitrogen in sure/seal bottle), tetra-n-butylammonium hydro- gen sulphate (TBAH) (all from Aldrich), 1 ,lo-phenanthroline (anhydrous, 99%), palladium(I1) diacetate (both from Lancas- ter Synthesis), acetyl chloride (99'/0) and (S)-(-)-2-methyl- butan-1-01 (95%) (both from Fluka) were used as received.Methylene chloride (Fisher) was purified by washing it with concentrated sulphuric acid several times until the acid layer remained colourless, then by washing with water, and drying it over anhydrous MgSO,, refluxing over calcium hydride and freshly distilling under argon before each use. Trifluoro- methane sulphonic acid (triflic acid, 98%, Aldrich) was distilled under vacuum. Techniques 'H NMR (200 MHz) spectra were recorded on a Varian XL- 200 spectrometer.Infrared (IR) spectra were recorded on a Perkin-Elmer 1320 infrared spectrophotometer. The thermal transition temperatures were measured by a Perkin-Elmer DSC-4 differential scanning calorimeter equipped with a TADS data station. In all cases, the heating and cooling rates were 20 "C min-l. The transition temperatures were reported J. MATER. CHEM., 1991, VOL. 1 Table 1 Cationic polymerization of (14-8y and characterization of resulting polymersb DP phase transitions1"C and corresponding enthalpy changes/kJ mol -sample no. [M]O/[I]Oyield(%) M, x 10-3 M,/M, GPC GPC GPC NMR heating cooling 1 5 77 2.72 1.09 6 7 g-7.1 Sc* 80.3 (0.29) SA 97.2 (4.99) I I 90.4 (4.75) SA 75.1 2 7 85 3.29 1.10 8 10 g-8.0 Sc* 80.0 (0.27) SA 97.1 (4.99) I g 1.0 Sc* 83.4 (0.26) SA 101.9 (5.08) I (0.27) Sc* -12.1 g I 95.9 (4.84) SA 78.0 (0.33) Sc* -7.2 g 3 10 73 4.86 1.08 11 14 g-3.9 Sc* 82.8 (0.24) SA 102.1 (4.95) I g 5.1 Sc* 89.6 (0.24) SA 111.1 (4.47) I I 104.9 (4.42) SA 84.9 (0.33) Sc* 0.2 g 4 5 13 17 83 80 5.71 7.29 1.06 1.08 13 17 19 23 g 2.7 Sc* 89.3 (0.38) SA 11 1.5 (4.56) I g 10.2 Sx (21.2 (0.42) Sc* 92.9 (0.37) SA 115.6 (4.71) I 115.6 (4.62) I 119.1 (4.42) g 8.0 Sx 21.1 (0.48) Sc* 92.8 (0.34) SA g 25.7 Sx 37.0 (1.70) Sc* 96.1 (0.29)SA g 22.5 Sx 31.8 (0.59) Sc* 96.1 (0.38 ) SA I 108.9 (4.56) SA 88.3 (0.44) Sc* 13.5 (0.55) Sx 5.1 g I 112.8 (4.51) SA 91.9 (0.44) Sc* (1.08) Sx 19.0 g 6 25 88 10.2 1.10 23 38 119.2 (4.40) I 123.6 (4.40) g 34.5 Sx 47.2 (2.75) Sc* 99.8 (0.37) SA g 27.6 Sx 44.5 (1.36) Sc* 99.8 (0.49) SA I 116.4 (4.34 SA 94.7 (0.29) Sc* 32.9 (1.65) Sx 22.5 g 123.5 (4.34) I) Polymerization temperature, 0 "C; polymerization solvent, methylene chloride; [MIo =0.244; [(CH3)zS]o/[I]o =20; polymerization time, 1 h.Data on first line are from first heating and cooling scans. Data on second line are from second heating scan Table 2 Cationic copolymerization of 14-1 1 with 14-8" and characterization of resulting polymersb ~~~~~~~~~ phase transitions/"C and corresponding enthalpy changes/kcal mol -sample [14-11]/[14-8) no. (mol/mol) yield(%) MWIM" M, x lop3 GPC DP heating cooling 1 Oil0 85 5.7 1.06 13 g 10.2 Sx 21.2 (0.42) Sc* 92.9 (0.37) SA 115.6 (4.62) I g 8.0 Sx 21.1 (0.48) Sc* 92.8 (0.34) SA I 108.9 (4.56) SA 88.3 (0.44) Sc* 13.5 (4.55) Sx5.1 g 2 3 4 5 6 119 218 317 4/6 515 87 84 77 82 83 7.0 5.9 6.7 6.4 6.4 1.09 1.09 1.14 1.08 1.15 16 13 15 14 15 115.6 (4.62) 1 g 7.2 Sc* 83.1 (0.44) SA 116.5 (4.87) I g 5.2 Sc* 83.3 (0.39) SA 116.3 (4.72) 1 g 9.0 Sc* 76.6 (0.28) SA 118.2 (4.64) I g 6.1 Sc* 76.6 (0.34) SA 118.5 (4.64) I g 4.5 Sc* 63.6 (0.23) SA 113.4 (4.66) I g 4.2 Sc* 63.9 (0.17) SA 113.0 (4.72) I g 4.7 Sc* 52.8 (0.21) SA 115.3 (4.88) I g 3.3 Sc* 53.0 (0.17) SA 115.3 (4.94) 1 g 5.2 Sc* 43.4 (0.10) SA 115.2 (4.75) I I 109.9 (4.82) SA 77.9 (0.30) Sc* 1.7 g I 110.9 (4.49) SA 71.3 (0.34) Sc* 1.7 g I 108.2 (4.53) SA 60.2 (0.25) Sc* -0.5 g I 109.4 (4.86) SA 48.7 (0.17) Sc* -0.2 g I 111.6 (4.98) SA 41.8 (0.17) Sc* -0.2 g 7 8 9 10 614 713 812 911 85 79 81 80 6.3 7.0 6.8 7.1 1.07 1.13 1.15 1.12 14 15 15 15 g 2.5 Sc* 45.5 (0.10) SA 116.8 (5.00) I g 5.2 Sc* 40.1 (0.10) SA 115.2 (5.01) I g 3.2 Sc* 40.0 (0.10)SA 115.3 (5.22) I g 5.2 Sx 14.4 (0.25) Sc* 41.3 (0.04) SA 117.0 (5.29) I 117.2 (5.19) I 116.7 (5.22) I 117.1 (5.32) I g 3.7 Sx 14.1 (0.40) Sc* 41.3 (0.02) SA g 6.6 Sx 16.5 (0.63) Sc* 40.6 (0.02) SA g 3.3 Sx 16.2 (0.28) Sc* 41.2 (0.06) SA g 9.0 K 50.3 (9.71) SA 120.1 (5.60) I I 109.4 (5.16) SA 35.7 (0.08) Sc* 0.7 g I 110.9 (5.25) SA 36.9 (0.18) Sc* 8.8 (0.14) Sx 1.6 g I 111.4 (5.24) SA 37.1 (0.08) Sc* 10.1 (0.73) Sx 1.6 g I 113.0 (5.30) SA 39.6 (0.14) Sc* 12.9 (1.32) Sx 3.5 g 11 1010 93 8.2 1.12 17 g 6.6 Sx 21.1 (1.48) Sc* 44.3 (0.08) SA 119.8 (5.44) I g 10.1 K 57.1 (12.90) SA 118.1 (5.69) I g 8.2 Sx 24.9 (2.10) Sc* 52.2 (0.17) SA 118.1 (5.56) I I 112.3 (5.35) SA 48.4 (0.17) Sc* 15.6 (2.05) Sx 7.9 g a Polymerization temperature, 0 "C; polymerization solvent, methylene chloride; [MIo =[14-11]+ [14-8]=0.208-0.244 mol dm-3; [M]o/[I]o = 15; [(CH3)zS]o/[I]o= 10; polymerization time, 1 h.Data on first line are from first heating and cooling scans. Data on second line are from second heating scan J. MATER. CHEM., 1991, VOL. 1 as the maxima and minima of their endothermic and exother- mic peaks. Glass-transition temperatures (TB)were read at the middle of the change in the heat capacity. A Carl-Zeiss optical polarized microscope (magnification 100 x) equipped with a Mettler FP 82 hot stage and a Mettler FP 80 central processor was used to verify the thermal transitions and to characterize the anisotropic textures.Relative molecular weights of polymers were measured by gel permeation chrom- atography (GPC) with a Perkin-Elmer Series 10 LC instru-ment equipped with LC-100 column oven and a Nelson Analytical 900 series integrator data station. A set of two Perkin-Elmer PL gel columns of 5x102 and 104A with CHC13 as solvent (1 cm3 min-') were used. The measurements were made at 40"C using the UV detector. Polystyrene standards were used for the calibration plot. High-pressure liquid chromatography (HPLC) experiments were performed with the same instrument. 1 cycoc12 * AICb.CHzCIz 3 (1) NaOBr 3 >(2)HCI 48% HBr4 CH3COzH 5 KOH 5 CH30H 13 Synthesis of (S)-(-)-2-MethylbutyI 4-(8-vinyloxyoctyloxy) biphenyl-4-carboxylate and (S)-(-)-2-Methylbutyl 4'4 11-uinyl-oxyundecanyloxy)biphenyl-4-carboxylate Both monomers 14-8 and 14-11 were synthesized according to the synthetic route outlined in Scheme 1. Compounds 3, 4, 5, 6, 8, 13 and monomer 14-11 were synthesized as described previously.6g Synthesis of 8-Bromooctan-1-ol (10) A solution of borane-THF complex (180 cm3) was stirred in a 1000 cm3 three-neck round-bottom flask for 30 min in an ice bath under nitrogen. A solution of 21.4 g (0.096 mol) of 8-bromooctanoic acid in 220 cm3 of dry THF was then added dropwise over a period of 4-5 h.23 After stirring for a further 3 h in an ice bath, 10 cm3 H20 followed by 120 cm3 saturated C H3CH'C F3S03- I Q I C02R' (R9=-CH2CHCH2CH3)I CH3 !I14-8 CH3CHS'(CH3)2CF$SOLI0I (CH2)eI08\Q CO2R' CO2R' CH3C H (CH2C H) -2CH2CH 'C F3S03- I I 00 I08\ (n411) 14-n C02R' Scheme 1 Synthesis of (S)-(-)-2-methylbuty14( 11-vinyloxyundecanyl-oxy)biphenyl-4-carboxylate (14-11) and (S)-(-)-2-methylbutyl 4'-(8-Scheme 2 Cationic polymerization of (S)-(-)-2-methylbutyl 4'-(8-vinyloxyoctyloxy)biphenyl-4-carboxylate(14-8) vinyloxyoctyloxy)biphenyl-4-carboxylate(14-8) ioia J.MATER. CHEM., 1991, VOL. 1 qh rnh rnej CH3CH (CH CH), -2CH2CHOCHs I 7 I 0 0 0 CH2 CH2 CH2 i CH2 CH2 CH2 n (CH2)4 (CH2)4 (CH2)4 0 CH2 CH2 CH2 I 0,PCH2 CH2 CH2 (1.34) 876543 c=o c=o c=o I I I 1 I I I 1 I I 9 8 7 6 5 4 3 2 1 0 6 (PPm) Fig.1 200 MHz 'H NMR spectrum of poly(14-8) with theoretical DP =8 K2C03 solution were added slowly to the reaction mixture. stirring for 2 h at 60 "C, the mixture turned yellow. Then, The THF solution was separated and the water layer was 8-bromooctyl vinyl ether (3.31 g, 0.014 mol) and 5 cm3 of dry extracted with THF twice. The combined THF solution was DMSO were added and the reaction mixture was stirred for dried over MgSO,. After the THF was evaporated on a rotary 20 h at 60 "C.The reaction mixture was poured into 250 cm3 evaporator, the resulting pale-yellow oil was distilled under of water to give a white precipitate, which was extracted with vacuum.The portion distilling at 90-92 "Cl0.l 1 mmHg was chloroform. The chloroform solution was dried over MgS0, collected to yield 16.0 g of a colourless liquid (80%). dH and the solvent was removed in a rotary evaporator. The (200 MHz; solvent CDCl,; standard Me,Si) 3.65 (2 H, t, resulting solid was recrystallized from methanol and was -OCH2-), 3.41 (2 H, t, BrCH2-), 1.86 (2 H, m, -OCH,CH,-), 1,57 (2 H, m, BrCH,CH,-), 1.34 [8 H, m, BrCH,CH,(CH,),-1. *O'Synthesis of 8-Brornooctyl Vinyl Ether (12) A solution of 8-bromooctan-1-01 (10) (15.5 g, 0.0742 mol), H16 -1,lO-phenanthroline palladium(r~) diacetate,, (0.97 g, 2.39 mmol), butyl vinyl ether (190 cm3) and 20 cm3 dry chloro- form was refluxed overnight (12-14 h).'=ve The resulting pale- 7 12-7 yellow solution, obtained after gravity filtration, was placed 0 ron a rotary evaporator to remove the excess butyl vinyl ether H OX and chloroform.The remaining yellow oil was purified by column chromatography (silica gel, CHzC12 as element) to yield 16.36 g (94%) of a pale-yellow oil. dH (200 MHz; solvent CDC13; standard Me,%) 6.49-6.38 (1 H, m, CH,CHO-), 4.14 (1 H, d, Z-CH,CHO-), 3.93 (1 H, d, E-CH,CHO-), 3.64 (2 H, t, CH2CHOCH2-), 3.38 (2 H, t, BrCH2-), 1.82 (2 H, m, -OCH,CH,-), 1.61 (2 H, m, BrCH,CH,-), 1.27 AAAA A A [8 H, m, BrCH,CH,(CH,),-1. 1 I I I 1 0 5 10 15 20 25 Synthesis of (S)-(-)-2-Methylbutyl 4'-( 8-uinyloxyoctyloxy) [Ml,/[Il, biphenyl-4-carboxy late (14-8) Fig. 2 Dependence of the number-average molecular weight (M,)To a mixture of potassium carbonate (5.9 g, 0.0378 mol) and determined by GPC (0)and NMR (W) and of the polydispersity 90 cm3 of acetone were added 4.3 g (0.015 mol) of 13.After (M,/M,) (A)of poly (14-8) on the [M]o/[I]o ratio J. MATER. CHEM., 1991, VOL. 1 1019 further purified by column chromatography (silica gel, CH2C12 Cationic Polymerizations as eluent) to give 2.2 g (36%)of white crystals. Purity: 99.9% Polymerizations were carried out in glass flasks equipped (HPLC). Thermal transition temperatures ( "C) are: K 37.6 SA with Teflon stopcocks and rubber septa under argon atmos- 53.3 I on heating, and I 49.2 SA 30.2 Sc* -15.6K on cooling phere at 0 "C for 1 h. All glassware was dried overnight at (DSC); dH (200 MHz solvent CDCl,; standard Me,Si) 180 "C.The monomer was further dried under vacuum over- 1.00 [6 H, m, -CH(CH3)CH2CH3], 1.37 [lo H, night in the polymerization flask. After the flask was filled m,-OCH2CH2(CH2),-, and-CHCH2CH3], 1.64 (2 H, m, with argon, freshly distilled dry methylene chloride was added -CCH2CH20Ph-), 1.78 [3 H, m, =CHOCH2CH2-, through a syringe and the solution was cooled to 0°C. and-CH2CH(CH3)CH2-1, 3.69 (2 H, t,=CHOCH,-), Dimethyl sulphide and triflic acid were then added carefully 4.01 (3H, m, -CH20Ph and =CH2 trans), 4.18 (3H, m, via a syringe.25 The monomer concentration was ca. 10 wt.% C02CH2-and =CH2 cis), 6.43-6.50 (I H, m, =CHO-), of the solvent volume and the dimethyl sulphide concentration 6.98 [2 ArH, d, ortho to-O(CH,),-], 7.56 [2 ArH, d, meta was x10 larger than that of the initiator.The polymer to-O(CH,),-1, 7.62 (ArH, d, meta to -CO,-), 8.06 molecular weight was controlled by the monomer/initiator (2 ArH, d, ortho to -C02-). ([M]o/[I]o) ratio. After the polymerization had been quenched 6 11 SC* SA il t 13 z W -10 20 50 80 110 140 -10 20 50 80 110 140 -10 20 50 80 110 T/"C T/"C T/"C Fig. 3 DSC traces displayed during the first heating scan (a), the second heating scan (b) and the first cooling scan (c) by poly(14-8) with different DP determined by GPC. DP is printed on the top of each DSC scan H -(CH2CH) ACH2C H) ,OC H3 CH2=$H I I0 0 0I I I (CH2)E (CH2)11I 10 0 Q QQ CO,R' C02R' C02W CO*W 14-8 14-1 1 a (R'=-CH&HCH&H3)1 CH3 Scheme 3 Cationic copolymerization of 14-11 and 14-8 J.MATER. CHEM., 1991, VOL. 1 with ammoniacal methanol, the reaction mixture was precipi- 150 tated into methanol. The filtered polymers were dried, and precipitated from methylene chloride solution into methanol several times until GPC traces showed no unreacted monomer. The polymerization results are summarized in Tables 1 and 2. Results and Discussion In the area of low-molar-mass liquid crystals there are some empirical rules which can be used to design compounds displaying chiral smectic C (Sc*) mesophases.26 Such rules are not available for the design of side-chain liquid-crystalline polymers exhibiting Sc* pha~es.~g.'-~~We decided, therefore, to perform a series of systematic investigations aimed to derive empirical rules useful for the molecular engineering of side-chain liquid-crystalline polymers exhibiting Sc* meso-phases. Based on our previous experience on the molecular engineering of nematic and smectic phases, the first require- ment for such an investigation would be to have available two homopolymers displaying the same mesophase and also to know the influence of molecular weight on their phase- transition temperature^.^,^ Copolymerization experiments can then be used to enlarge the thermal stability of a certain me~ophase.~ The data presented in this manuscript will follow the same pattern.We have already information on the influence of molecular weight on the phase transitions of poly(l4-11) which exhibits an Sc* phase.6g The next step is to provide a second polymer for which we will have the same information, i.e.p01y( 14-8). Scheme 1 outlines the synthesis of 14-8. Experimental details for all intermediate steps have been published previously.6g The cationic polymerization of 14-8 was initiated with the system CF3S03H/S(CH3)2 and was performed at 0°C in CH2C12.25 It is essential that the monomers used in these polymerization experiments are completely free of protonic impurities. In order to achieve this degree of purity, after the purification by conventional techniques, the monomer is passed through a chromatographic column containing silica gel using methylene chloride as eluent.The polymerization mechanism is presented in Scheme 2 and the polymerization results of 14-8 are summarized in Table 1. Polymer yields are lower than expected, owing to the polymer loss during the purification process. Although the molecular weights deter- mined by GPC reported in Table 1 are relative to polystyrene standards, they demonstrate that the ratio of [M]o/[I]o pro- vides a very good control of the polymer molecular weight. In addition, all polydispersities are <1.15. Absolute number- average molecular weights and DPs were determined by 200 MHz 'H NMR spectroscopy. A representative 'H NMR spectrum together with its protonic assignments is presented in Fig. 1. The DP was determined by measuring the ratio of the doublet at 6=6.92 ppm uersus the broad triplet at 6 = 4.63 ppm.The DP determined by both GPC and NMR are summarized in Table 1. The number-average molecular weights of poly(14-8) determined by both GPC and NMR and the M,/M, data are plotted in Fig. 2 as a function of [M],/[I], ratio. All three dependences are linear, demonstrat- ing a living polymerization mechanism. The difference between the two slopes of the dependences of Mn us. [Ml0/[I], is expected since one set of data (from NMR) is absolute while the other (from GPC) is relative. Fig. 3 presents the DSC traces of the first and second heating and first cooling scans. It can be seen that first and second heating scans are almost identical. Regardless of DP all poly(14-8)s exhibit enantiotropic SA and Sc* mesophases.The assignment of these mesophases was confirmed by thermal optical polarized microscopy. Representative textures dis-no A:,i90 AA -30 ! II I I I 0 5 1b 15 20 25 30 a m aa SA Dm A A 90 Ah AA SC* 0 e SX0 00, 0-1''1 0 ' 00 I glassy -30 ! 10 15 20 251 I I 1 I 0 5 I l3OI110 'n. AL 10 -300 0 °4-11 glassy 0 5 10 15 20 25 30 DP Fig. 4 Dependence of phase transition temperatures on DP deter-mined by GPC of poly(14-8). (a) Data from first heating scan: (0) T,; (0) T(SA-I); (b)data from second T(Sx-Sc*);(A)T(S,*-S,); (0) heating scan: (0)T,; (0)T(Sx-Sc*);(A)T(Sc*-SA); (0)T(SA-I); (c) data from first cooling scan: (a)T(I-SA); (A)T(SA-Sc*);(+) T(Sc*-Sw); (0)T, played by the SAand Sc* mesophases are presented in Plate 1.Only poly(14-8)s with DP 13, 17 and 23 present an enanti- otropic unidentified Sx mesophase. The lower-molecular- weight polymers do not show' this Sx phase since this transition temperature overlaps the glass-transition temperature and is therefore strongly controlled by kinetics. Since even the Sx J. MATER. CHEM., 1991, VOL. 1 (a) Plate 1 Representative optical polarized micrographs (x 100) of (a) the S, mesophase displayed by poly(14-8), DP=23 at 102 "Con the cooling scans; (b)the S,* mesophase displayed by poly(14-8), DP=23, at 75 "Con the cooling scan V. Percec et al. (Facing p. 1020) J. MATER. CHEM., 1991, VOL. 1 I 011osx sc*4J 1I9 t B z w -10 20 50 80 110 1 -10 20 50 80 110 0 -70 20 50 80 110 140 T/"C T/"C TI"C traces displayed during (a) the first heating scan, (b) the first cooling scan and (c) the second heating scan by poly Fig.5 DSC (14-8-~0-14-ll)X/Y.X/Y is shown above each trace on the left phase of the high-molecular-weight poly(14-8) is close to Tg of the polymer, no representative texture could be obtained for this phase. The dependences between various phase- transition temperatures and DP of poly(14-8) are plotted in Fig. 4. Poly(l4-11)s exhibit in the first heating and cooling scans a crystalline phase, an enantiotropic SA and a mono- tropic Sc* phase. In the second heating scan, because of the close proximity of the crystallization temperature to the polymer phase transition, the crystallization process does not take place and hence the polymers exhibit enantiotropic Sx, Sc* and SA mesophases.6g In general, since crystallization is a kinetically controlled process while the formation of a mesophase is a thermodynamically controlled process, the crystallization process is different for various DSC scans while mesomorphic phase transitions are not.The copolymerization of 14-11 with 14-8 is outlined in Scheme 3 and the results are summarized in Table 2. Attempts were made to synthesize poly(14-8-co-14-ll) X/Y (where X/Y refers to the mole ratio of the two structural units) copolymers with DP x15. Fig. 5 presents the DSC traces of poly(14-8-co-14-ll) X/Y obtained during the first and second heating and first cooling scans.Poly(14-8-co-14-ll) X/Y with X/Y = 1/9-6/4 exhibit enantriotropic Sc* and SA mesophases. Therefore, the struc- tural units of poly(14-8) and poly(l4-11) are isomorphic in their SA and Sc* mesophases but are not isomorphic in their Sx phases. Subsequently the Sx phases of poly(14-8) and poly(l4-11) are different. Therefore, as expected from the results obtained with other copolymer system~,~ cationic copolymerization of 14-8 with 14-11 allowed the synthesis of copolymers with a low Tg and a very broad range for the Sc* mesophase. This can be observed from Fig. 6 which plots the phase behaviour of poly(14-8-co-14-11) as a function of copolymer composition. These copolymerization experiments demonstrate the ability to engineer Sc* mesophases by living cationic copoly- merization experiments.Such experiments will allow a quanti- tative investigation of the dynamics of Sc* parameters us. various structural variants of the polymer and hence will contribute to the molecular engineering of ferroelectric liquid- crystalline elastomersgb with well defined architecture. Financial support from the Office of Naval Research is gratefully acknowledged. References (a)J. M. Rodriguez-Parada and V. Percec, J. Polym. Sci., Polym. Chem. Ed., 1986, 29, 327; (b)V. Percec and D. Tomazos, Polym. Bull., 1987, 18, 239; (c) V. Percec, Makromol. Chem., Makromol. Symp., 1988, 13/14, 397. (a) T. Sagane and R. W. Lenz, Polym. J., 1988, 20, 923; (b) T.Sagane and R. W. Lenz, Polymer, 1989, 30, 2269; (c) T. Sagane and R. W. Lenz, Macromolecules, 1989, 22, 3763. S. G. Kostromin, N. D. Cuong, E. S. Garina and V. P. Shibaev, Mol. Cryst. Liq. Cryst., 1990, 193, 177. (a) V. Heroguez, A. Deffieux and M. Fontanille, Makromol. Chem., Makromol. Symp., 1990, 32, 199; (b) V. Herogeuz, M. Schappacher, E. Papon and A. Deffieux, Polym. Bull., 1991, 25, 307. (a) V. Percec, M. Lee and H. Jonsson, J. Polym. Sci., Polym. Chem. Ed., 1991, 29, 327; (b)V. Percec and M. Lee, Macromol-ecules, 1991, 24, 1017; (c) V. Percec and M. Lee, Macromolecules, 1991,24, 2780; (d) V. Percec, M. Lee and C. Ackerman, Polymer, in the press; (e)V. Percec and M. Lee, J. Macromol. Sci., Chem., 1991, A28, 651.(a) V. Percec, A. Gomes and M. Lee, J. Polym. Sci., Polym. Chem. Ed., in the press; (b)H. Jonsson, V. Percec and A. Hult, Polym. Bull., 1991, 25, 115; (c) R. Rodenhouse and V. Percec, Adu. Muter., 1991, 3, 101; (6) R. Rodenhouse and V. Percec, Polym. Bull., 1991, 25, 47; (e) R. Rodenhouse, V. Percec and A. I022 SA”“5‘-* ‘A glassy ‘A SA \A L-50 30 glassy-10 I I I 1 0.0 0.2 0.4 0.6 0.8 1 .o SA‘A ‘A ‘A 50 30 SC* SX<--.--* /- 0 -0- a-0- a-0 -0-0- -1 0 I I glassy 1 1 0.0 0.2 0.4 0.6 0.8 1.o DP Fig. 6 Dependence of phase-transition temperatures on DP of poly (14-8-~0-14-ll)X/Y.(a) Data from first heating: (0)T,; (0)T(S,-Sc*); (A) T(Sc*-SA);(0)T(SA-I); (b)data from second heating scan: (0)Tg;(0)T(Sx-Sc*); (4) T(Sc*-S,); (I)T(SA-I); (c) data from first cooling scan: (H) T(I-SA); (A)T(SA-Sc*);(+) T(Sc*-S,); (e)Tg E.Feiring, J. Polym. Sci., Polym. Lett., 1990, 28, 345; (f) V. Percec, C. S. Wang and M. Lee, Polym. Bull., 1991, 26, 15; (g) V. Percec, Q. Zheng and M. Lee, J. Mater. Chem., 1991, 1, 611. 7 (a) V. Percec and M. Lee, Polymer, in the press; (b) V. Percec and M. Lee, Polym. Bull., 1991, 25, 123; (c) V. Percec and M. Lee, Polym. Bull., 1991, 25, 131; (d) V. Percec and M. Lee, J. MATER. CHEM., 1991, VOL. 1 Macromolecules, 1991, 24, 4963; (e) V. Percec and M. Lee, J. Mater. Chem., 1991, 1, 1007. V. P. Shibaev and Ya. S. Freidzon, in Side Chain Liquid Crystal Polymers, ed. C. B. McArdle, Chapman and Hall, New York, 1989, p.260. (a) P. LeBarny and J. C. Dubois, in Side Chain Liquid Crystal Polymers, ed. C. B. McArdle, Chapman and Hall, New York, 1989, p. 130; (b)J. H. Wendorff, Angew. Chem., Znt. Ed. Engl., 199 1, 30, 405, and references therein. 10 J. W. Goodby, M. A. Waugh, S. M. Stein, E. Chin, R. Pindak and J. S. Patel, J. Am. Chem. SOC., 1989, 111, 8119. 11 (a)V. P. Shibaev, M. V. Kozlovsky, L. A. Beresnev, L. M. Blinov and N. A. Plate, Polym. Bull., 1984, 12, 299; (b) V. P. Shibaev, M. V. Kozlovsky, N. A. Plate, L. A. Beresnev and L. M. Blinov, Polym. Sci. USSR (Engl. Transl.), 1987, 29, 1616; (c) L. M. Blinov, V. A. Baikalov, M. J. Barnik, L. A. Beresnev, E. P. Pozhidayev and S. V. Yablonsky, Liq. Cryst., 1987, 2, 121.12 (a) G. Decobert, F. Soyer and J. C. Dubois, Polym. Bull., 1985, 14, 179; (b)J. M. Guglielminetti, G. Decobert and J. C. Dubois, Polym. Bull., 1986, 16, 411; (c) J. C. Dubois, G. Decobert, P. LeBarny, S. Esselin, C. Friedrich and C. Noel, ,4401. Cryst. Liq. Cryst., 1986, 137, 349; (d) G. Decobert, J. C. Dubois, S. Esselin and C. Noel, Liq. Cryst., 1986, 1, 307; (e) S. Esselin, L. Bosios, C. Noel, G. Decobert and J. C. Dubois, Liq. Cryst., 1987, 2, 505; (f) S. Esselin, C. Noel, G. Decobert and J. C. Dubois, Mol. Cryst. Liq. Cryst., 1988, 155, 371. 13 (a) R. Zentel, G. Reckert and B. Reck, Liq. Cryst., 1987, 2, 83; (b)S. Bualek and R. Zentel, Makromol. Chem., 1988, 189, 797; (c) H. Kapitza and R. Zentel, Makromol. Chem., 1988, 189, 1793; (d)S.Bualek, H. Kapitza, J. Meyer, G. F. Schmidt and R. Zentel, Mol. Cryst. Liq. Cryst., 1988, 155, 47; (e) S. U. Vallerien, R. Zentel, F. Kremer, H. Kapitza and E. W. Fischer, Makromol. Chem. Rapid Commun., 1989, 10, 333; (f) R. Zentel, H. Kapitza, F. Kremer and S. U. Vallerien, in Liquid Crystalline Polymers, ed. R. A. Weiss and C. K. Ober, ACS Symposium Series 435, Washington DC, 1990, p. 207. 14 (a) S. Uchida, K. Morita, K. Miyoshi, K. Hashimoto and K Kawasaki, Mol. Cryst. Liq. Cryst., 1988, 155, 93; (b)H. Endo, S. Hachiya, S. Uchida, K. Hashimoto and K. Kawasaki, Liq. Cryst., 1991, 9, 635. 15 N. Koide, K. Uehara and K. Iimura, Mol. Cryst. Liq. Cryst., 1988, 157, 151. 16 T. Suzuki, T. Okawa, K. Ohnuma and Y. Sakon, Makromol. Chem.Rapid Commun., 1988, 9, 755. 17 M. Dumon, H. T. Nguyen, M. Mauzac, C. Destrade, M. F. Achard and H. Gasparoux, Macromolecules, 1990, 23, 355. 18 D. M. Walba, P. Keller, D. S. Parmar, N. A. Clark and M. D. Wand, J. Am. Chem. SOC., 1989, 111, 8273. 19 H. Kapitza, R. Zentel, R. J. Twieg, C. Nguyen, S. U. Vallerien, F. Kremer and C. G. Wilson, Adv. Mater., 1990, 2, 539. 20 T. Kitazume, T. Ohnogi and K. Ito, J. Am. Chem. SOC., 1990, 112, 6608. 21 (a) H. J. Cole, H. F. Gleeson, G. Scherowsky and A. Schliwa, Mol. Cryst. Liq. Cryst., 1990, 7, 117, 125; (b)H. M. Colquhoun, C. C. Dudman, C. A. O’Makoney, G. C. Robinson and D. J. Williams, Adv. Mater., 1990, 2, 139. 22 (a) V. Percec and C. S. Wang, J. Macromol. Sci. Chem., 1991, A28,687; (b)V. Percec and C. S. Wang, J. Macromol. Sci.Chem., 1991, A28, 687; (c) V. Percec, C. S. Wang and M. Lee, Polym. Bull., 1991, 26, 15. 23 N. M. Yoon, C. S. Pak, H. C. Brown, S. Krishnamurthy and T. P. Stocky, J. Org. Chem., 1973, 38, 2786. 24 J. E. McKeon and P. Fitton, Tetrahedron, 1972, 28, 233. 25 (a) C. G. Cho, B. A. Feit and 0. W. Webster, Macromolecules, 1990, 23, 1918; (b) C. H. Lin and K. Matyjaszewsky, Polym. Prepr.. Am. Chem. SOC.Div. Polym. Chem., 1990, 31(1), 599. 26 (a)G. W. Gray and J. W. Goodby, Mol. Cryst. Liq. Cryst., 1976, 37, 157; (b)G. W. Gray and J. W. Goodby, Mol. Crystl. Liq. Cryst., 1978, 48, 127; (c) G. W. Gray, M. Hird, D. Lacey and K. J. Toyne, Mol. Cryst. Liq. Cryst., 1990, 191, 1; (d)D. Demus, H. Demus and H. Zaschke, Flussige Kristalle in Tabellen, VEB Deutscher Verlag fur Grundstoffindustrie, Leipzig, I974 and 1984, vol. I and 11; (e)D. M. Walba, C. S. Slater, W. N. Thurmes, N. A. Clark, M. A. Handsky and F. Supon, J. Am. Chem. SOC., 1986, 108, 5210. Paper 11024995;Received 28th May, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910101015

出版商:RSC    

年代:1991

数据来源: RSC

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J. MATER. CHEM., 1991, 1(6), 1023-1025 Structure and Conductivity of an Li,SiO,-Li,SO, Solid Solution Phase M. A. K. L. Dissanayake" and Anthony R. Westb "Department of Physics, University of Peradeniya, Peradeniya, Sri Lanka bDepartment of Chemistry, University of Aberdeen, Meston Walk, Aberdeen A59 2UE, UK In the system Li4Si04-Li,S04, phase-diagram studies show the existence of a narrow range of stable y solid solutions, Li4-2pw(Si, -xS,)04: 0.30<x< 0.045. These have high Li+ ion conductivity with maximum values for xz0.40 of 1.32 x S cm-' at 25 "C, rising to 8.5 x S cm-' at 300 "C and an activation energy of 0.80 eV. The y solid solutions are structurally related to orthorhombic y-Li,PO, and contain interstitial Li' ions; for x= 0.40, a=6.187(2) A, b=10.621(3) A, c=5.008(3) A.Keywords: Lithium ion conductor; Lithium silicate ; Lithiiim sulphate ; Solid electrolyte A number of solid solutions based on Li4Si04 are reported to have high lithium ion conductivity. These include: (i) stoichiometric solid solutions with Li,GeO, and Li4Ti04 whose conductivity is increased only moderately at intermedi- ate compositions;',2 (ii) interstitial Li+ solid solutions with Li,A104 and Li,Ga04 which have greatly increased conduc- tivity;,~~and (iii) vacancy solid solutions with Li3X04, X= P,As,V, and Liz ,5(A1,Ga)o .,SO4, which also have greatly increased c~nductivity.~-'~. ?-Tetrahedral structure phases such as Li3X04: X=P,As,V and Li2ZnGe04 also have high Li ion conductivity when they form solid solutions contain- + ing interstitial Li+ The literature on the system Li4Si04-Li2S04 is rather confusing.Shannon et a!., were the first to report high Li' ion conductivity and attributed it to the creation of Li' vacancies in the Li4Si04 structure; they obtained a conduc- tivity of 1 x S cm-' at 300 "C for composition Li, .4(Sio ,7So,3)04. Burmakin and Zhidovinova reported a change-over from the monoclinic Li,Si04 structure to an orthorhombic structure at 30-35% Li2S04, but without any sudden change in electrical properties. ' ' Neutron diffraction studies on composition Li, .4(Si0 .,So.3)04 showed it to be orthorhoinbic and based on the y-Li3P04 structure, but containing interstitial Li+ ions.16 Given these rather conflict- ing results and the fact that the structures of Li,Si04 and Li3P04 are significantly different, we have made a combined phase diagram, X-ray diffraction and conductivity study in order to resolve these differences, and the results are reported here.Experimental Lithium orthosilicate, Li,Si04 was prepared by solid-state reaction of Si02 (high-purity crushed quartz crystal) and Li2C03 (BDH, AnalaR). Completeness of reaction was checked by X-ray powder diffraction using a Shimadzu model XD-7A X-ray diffractometer with Cu-Ka, radiation of wave- length 1.54188,. Mixtures of Li,Si04 and Li2S04 (BDH, AnalaR) in various proportions were heated at 600-700 "C for 12 h in gold-foil boats. Pellets of the reacted mixtures were cold-pressed at 2 tons cm-2 and sintered at 900-1000 "C for 12-24 h.Electrodes made from Engelhard liquid-gold paste were attached to the pellets, whose temperature was gradually raised to 800 "C in order to decompose the organometallic paste and harden the electrodes. The pellets were subsequently placed inside a high-temperature sample holder" which was inserted into a Heraeus tube furnace controlled by a Euro- therm 810 temperature controller, and the conductivity was determined by a.c. impedance measurements over the range 10 Hz-10 MHz with a Hewlett-Packard 4192A LCR meter and HP86B microcomputer. Measurements were made at 25 "C intervals up to 600 "C on both heating and cooling. The signal applied to the sample was 20 mV, and the tempera- ture measured with a chromel-alumel thermocouple placed close to the pellet.For phase-diagram determination, approximate melting temperatures were determined by observing the appearance of pellets during stepwise heating in a muffle furnace. Since it is difficult to observe both the onset and completion of melting by this method, a single 'average' temperature was obtained for each composition which should lie somewhere between the solidus and liquidus temperatures. Phase-tran- sition and melting temperatures for some compositions were also determined using a Stanton Redcroft DTA 675, heating rate 5 "C min-'. Results and Discussion An approximate phase diagram for the system Li,SiO,- Li2S04, constructed using a combination of DTA results, pellet melting studies and room-temperature X-ray diffraction on samples reacted at high temperature, is shown in Fig.1. It contains a narrow range of solid solutions, labelled y, of formula Li, -2x(Sil-xS,)04: 0.30 <x<0.45, which are stable at all temperatures up to melting at 860-1060 "C. There was no evidence of any significant solid solution in either of the end-member phases, Li4Si04 and Li2S04. The y solid solutions appear to belong to the family of y phases, such as the Li3 +,(PI -,Si,)04 solid solutions, in accordance with the neutron diffraction results of composition x=0.3O.l6 Most y solid solutions are based on a parent end- member, such as Li3P04 or Li2ZnGe04, which have an overall cation:anion ratio of unity. In the present y solid solutions, there appears to be no such stoichiometric parent phase although the hypothetical composition x=0.5, outside the experimental solid solution range, would have a cat-ion:anion ratio of unity.Indexed powder diffraction data for one y composition have been tabulated.? The orthorhombic lattice parameters: a=6.187(2) A, b= 10.621(3)A, c= S.OOS(3)8, for x=0.40, are similar to those reported earlier, t Available from the authors on request; to be submitted to the JCPDS File. 1024 x in Li4_2x(Si,-,S,)04 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 liquid 1200p--.. i 1000 800 9.t-600 400 200 Li4sio4 10 20 30 40 50 60 70 80 90 Li2s04 mol Yo Fig. 1 Approximate phase diagram for the system Li,SiO,-Li,SO,.0, samples were single phase/two phase, respectively by X-ray powder diffraction; x ,DTA transition temperatures, heating at 8 "C min-I; 0,approximate melting temperature of pellets a=6.1701 A, b= 10.6550A, c=5.0175 A, for composition x =0.30.16 A.c. impedance data were used, in the form of complex- impedance plane plots, to extract net conductivity values. Generally, two semicircles were seen, one with a capacitance of ca. 2 pF attributable to the bulk resistance, and a second, with a capacitance of 10-20 pF, attributed to grain boundaries of constriction resistance type. l8 At lower frequencies, an inclined spike with an associated capacitance of ca. 5 pF was seen, supporting the idea that conduction is by Li' ions which are polarised at the blocking Au electrodes.Impedance data at three selected temperatures, showing this spike inclined at 65-70" to the horizontal, are given in Fig. 2. Conductivity Arrhenius plots are given in Fig. 3 for three y solid solution compositions; the three sets are fairly similar although x =0.40 has a slightly higher conductivity, 1.32 x 52-' cm-' at 25 "C, rising to 8.5 x lop3R-' cm-' at 300 "C, with an activation energy of 0.80 eV. Conductivity data for the two-phase mixtures, Li4Si04 +y and y +Li2S04, are much lower (Fig. 3) reflecting the fact that the end- members Li4Si04 and Li,S04 have only modest Li' ion 100 200 300 400 z '/Q Fig. 2 Complex impedance plots for three temperatures for Li3 .2(si0 .SSO .4)O4 J.MATER. CHEM., 1991, VOL. 1 2 1 70 I E 7 -1 c Y2 -2 b Y P,2 -3 -4 -5 -6 -0 1.5 2.0 2.5 3.0 3.5 4.0 103K/T Fig. 3 Conductivity Arrhenius plots for Li4-2x(Sil -.S,)O, compo-sitions conductivity. The conductivity data in Fig. 3 were fully revers- ible on cooling. The data at lowest x (0.10) show a change in slope at ca. 290 "C. These data are probably dominated by the majority phase in this sample, Li,SiO,, for which a change in slope at 290 "C has been reported and discussed.' These results give conductivity values similar to, but slightly lower than, those of Shannon et aL3 The difference is probably not significant and reflects the fact that our pellets were not fully densified. Thus, the conductivity data in Fig.3 are net pellet conductivities and the true bulk values are likely to be somewhat higher. The highest conductivities, around x=0.3-0.4, correspond to Li contents of Li3,4 to Li3.2. The value Li3,4 is close to the optimum observed in the systems, Li4Si04-Li3X04: X =P,As,V, i.e. Li3 ,4(Si0 ,4Xo &)4.8.9.12 Shannon et aL3 believed their highly conducting compo- sition, x=0.30, to be a vacancy solid solution based on Li4Si04, whereas our results, in agreement with Fitch et a1.,16 indicate the structure to be rather an Li' interstitial solid solution based on the y-Li3P04 structure. This misassignment is readily understandable since there is considerable similarity between the X-ray powder patterns of Li4Si04 and the y phase. Thus it appears that Burmakin and Zhidovinova,' while recognising the changeover from monoclinic to ortho- rhombic symmetry with increasing x, were unable to recognise the two-phase region of Li,Si04+y at low x values.We thank the British Council for financial support, the International Programmes in the Physical Sciences, Uppsala University, Sweden for providing equipment and training for the Solid Electrolytes research at Peradeniya, P. W. S. K. Bandaranayake and C. N. Wijayasekera for research assist- ance, R. P. Gunawardane for helpful discussions and SERC for research support (A. R. W.). References 1 A. R. West, J. Appl. Electrochem., 1973, 3, 327, 2 I. M. Hodge, M. D. Ingram and A. R. West, J. Am. Ceram. SOC., 1976, 59, 360. 3 R. D.Shannon, B. E. Taylor, A. D. English and T. Berzins, Electrochim. Acta, 1977, 22, 783. 4 K. Jackowska and A. R. West, J. Mater. Sci., 1983, 18, 2380. J. MATER. CHEM., 1991, VOL. 1 1025 5 P. Quintana, F. Velasco and A. R. West, Solid State Ionics, 1989, 12 A. R. Rodger, J. Kuwano and A. R. West, Solid State Ionics, 34, 149. 1985, 15, 185. 6 7 Y. Saito, T. Asai, K. Ado, H. Kageyama and 0. Nakamura, Solid State lonics, 1990, 4/41, 34. Y. W. Hu, I. D. Raistrick and R. A. Huggins, J. Electrochem. SOC., 1977, 124, 1240. 13 14 15 16 H. Y.-P. Hong, Muter. Res. Bull., 1978, 13, 117. W. H. Baur, Inorg. Nucl. Chem. Lett., 1980, 16, 525. P. G. Bruce and A. R. West, J. Solid State Chem., 1982, 44, 354. A. N. Fitch, B. E. F. Fender and J. Talbot, J. Solid State Chem., 8 9 A. Khorassani and A. R. West, Solid State Ionics, 1982, 7, 1. A. Khorassani and A. R. West, J. Solid State Chem., 1984, 53, 17 1984, 55, 14. M. A. K. L. Dissanayake and M. A. Careem, J. Phys. E., 1988, 369. 21, 1203. 10 A. Garcia, G. Torres-Treviiio and A. R. West, Solid State Zonics, 18 P. G. Bruce and A. R. West, J. Electrochem. SOC., 1983,130, 662. 1990, 40/41, 13. 11 E. I. Burmakin and S. V. Zhidovinova, Russ. J. Znorg. Chem., 1980, 25, 1108. Paper 11025538; Received 30th May, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910101023

出版商:RSC    

年代:1991

数据来源: RSC

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J. MATER. CHEM., 1991, 1(6), 1027-1029 New Antimonate-Vanadate with the Rutile Structure Josefa Isasi, Maria Luisa Veiga, Antonio Jerez, Maria Luisa Lopez and Carlos Pico* Departamento de Quimica Inorganica I, Universidad Complutense, Facultad de Ciencias Quimicas, 28040 Madrid, Spain VCrSbO, has been prepared and its magnetic and electronic properties investigated. The crystal structure was refined from X-ray powder diffraction by the Rietveld method. The unit cell is tetragonal (space group P4,/rnnm, Z=2),a=4.5708(4) A and c=3.0281(3) A. The compound is isostructural with the rutile phase FeNbO, and stoichiometric with respect to all three constituent metals atoms. The electron diffraction pattern is consistent with a tetragonal symmetry. Keywords: Rutile; Antirnonate ; Vanadate The ideal rutile structure may be described as an idealized hexagonal close-packed oxygen lattice with octahedrally co- ordinated metal ions forming edge-shared infinite chains along the [OOl] direction of the tetragonal unit cell (P4,lmnm).These chains are cross-linked by octahedra sharing corners to form an equal number of identical vacant channels. Cation- cation interactions often occur between metal ions in the c direction, with edge-sharing octahedra, resulting in anomal- ously short metal-metal distances, and/or some structural modifications of the rutile type' can occur. Previous work concerning vanadium and niobium mixed oxides with genera! formula M02 (CrVNbO,, FeVNb06, NiV2Nb2010, Cr2V2WOlo and Cr2Nb2WOlo)2-5 has been reported.It was shown that these compounds adopt the ideal rutile structure and form grossly non-stoichiometric phases with retention of this structure. The semiconducting, electronic and magnetic properties may be correlated with the number of unpaired d electrons introduced into the rutile network. In addition to these interesting properties, some of these oxides have been investigated for potential application in the photoelectrolysis of water6-and as possible cathode materials for high-energy- density secondary batteries." In the course of our research of the chemical and structural relationships between SbV oxocompounds and those of NbV and Tav congeners, this paper describes the synthesis, crystal structure, electronic and magnetic properties of the rutile phase VCrSbO6.Experimental VCrSb06 was prepared by heating a mixture (in evacuated silica glass tubes) of Cr203 (Merck), V,04 (Merck) and Sb205 synthesized in the stoichiometric ratio, at 1163 K for 24 h. The absence of impurity phases was established from electron diffraction patterns. Powder X-ray diffraction patterns were registered at rate of 0.1" (28) min-' by means of a Siemens D500 diffractometer powered by a Kristalloflex generator using Ni-filtered Cu-Ka radiation. A 28 step scan of 0.04" was used, and Rietveld's profile analysis method" was employed for refinement of X-ray diffraction results in the 20 range 10- 120" for observed reflections. Electron diffraction was performed with the electron micro- scope JEOL 2000 FX operating at 200 kV.The sample was crushed and dispersed in acetone. The magnetic susceptibility measurements were made in the temperature range 4.2-300K, using a DSM-5 pendule magnetometer. The maximum magnetic field was 14 kG with HdH/dz =29 kG2 cm -'. The set-up was calibrated with Hg[Co(SCN),] and Gd2(S04)3 and was independent of the magnetic field in the temperature range used in these experiments. For the electrical resistivity measurements, the pelletized sample was sintered at 1163 K for 24 h. The electrical resis- tivity was measured using the van der Pauw', method. Contacts were made via silver paint on the sample discs; their ohmic behaviour was established by measuring their current- voltage characteristics. Results and Discussion X-Ray diffraction results were analysed by means of the Rietveld method.The program used minimises the function x2 =(R,p/REXp)2 and the best reliability factors were calcu- lated for a rutile-like model: Rp=100 1[Yi-Yci]/C [Yi]=18.3 1 I Rw,=100 {C [Wi (Yi-YCi)2]/C[wiY2])1/2=22.5 1 I Rg=100 1[Zi-I,-i]/E [Zj]=8.08 I I -(1ci)''2]/1RF= 100 [(Ii)1/2 (Ii)l',=8.83 I I The reflection conditions: k+1=2n (for Okl) I=2n (001) and h=2n (hOO) are compatible with the space group P4,/ mum. The unit-cell parameters were refined to the values a= 4.5708(4) 8, and c=3.0281(3) A. The atomic coordinates and bond lengths for VCrSbO, are presented in Table 1. The good agreement between the observed and calculated diffraction profiles appears in Fig.1. Fig. 2 shows the rutile structure in which Cr, Sb, and V octahedra are statistically distributed, forming edge-shared infinite chains along the [00 1) direction of the tetragonal unit cell. These chains are cross-linked by other octahedra sharing corners. The metal-oxygen distances are in agreement with the sums of the ionic radii as given by Shannon.I3 Fig. 3 shows the electron diffraction pattern along zone axis [1 111, consistent with tetragonal symmetry. Mag- netic measurements were performed at 4.2-300 K and show that the magnetic behaviour us. temperature for VCrSbO, is dependent only on the crystal structure and the oxidation Table 1 Atomic coordinates and bond lengths for CrVSbO, atom site Cr, V, Sb 2a 0 4f M-0 = 1.892 A x 2 M-0=2.021 Ax4 X Y Z 0 0 0 0.2928(3) 0.2928(3) 0 Fig.1 The observed (dots), calculated (full line) and difference diffrac- tion profiles for VCrSbO, Fig. 2 The rutile structure: CrO,, VO, and SbO, octahedra statisti- cally distributed forming edge-shared infinite chains along the [OOI] direction J. MATER. CHEM., 1991, VOL. 1 states of the cations involved in the compound. The magnetic susceptibility follows a Curie-Weiss law above 180 K, and no maximum in the curve has been found in the temperature range 4.2-300K CFig.41. This effect showed that the metal ions do not have antiferromagnetic ordering (ie.the paramag- netic ions are randomly distributed and hence also are the antimony ones) and the sample showed paramagnetic behav- iour.The Curie constant was 2.1 1, which is consistent with that expected from the contributions of V4+ (s= l/2) and Cr3+ (s=3/2); the Weiss constant was 8= -24.01 K. The electrical conductivity us. l/T, was studied for CrVSbO, (Fig. 5). From the results, one can deduce that this oxide is a classical semiconductor according to the law CJ=CI~ exp(-AE/k,T). This compound has a conductivity at 01 1 1 I I 1 0 60 120 I80 240 300 TI Fig. 4 Temperature dependence of the molar susceptibility of VCrSbO, \ I I 2.0 3 .O 4.0 1O3KI7 Fig. 3 The electron diffraction pattern along the zone axis [1171 of VCrSbO, Fig. 5 In(Conductivity) us. 103/T J.MATER. CHEM., 1991, VOL. 1 1029 room temperature of a=2.16 x R-' cm-' with E,= 0.38 eV. The transport properties are a result of localization of the 3d3 electrons on the Cr3+ ions (and 4d" in Sb5+ ions) which are unlikely to participate in M-M bonding. Metallic interactions would therefore be limited and semiconducting 3 4 5 M. Greenblatt, K. R. Nair, W. H. McCarroll and J. V. Wszczak, Muter. Res. Bull., 1984, 19, 777. K. R. Nair, M. Greenblatt and W. H. McCarroll, Muter. Res. Bull., 1983, 18, 1257. K. R. Nair, M. Greenblatt and W. H. McCarroll, Muter. Res. Bull., 1981, 18, 305. behaviour would result in this compound. The disordered distribution of metal ions with different orbital energies is likely to be sufficient for semiconducting behaviour.6 7 B. Khazai, R. Kershaw, K. Dwight and A. Wold, J. Solid State Chem., 1981, 39, 395. B. Khazai, R. Kershaw, K. Dwight and A. Wold, J. Solid State Chem., 1981,39, 294. We thank F. Rojas for the magnetic measurements. This work 8 H. Leiva, K. Dwight and A. Wold, J. Solid State Chem., 1982, 41, 42. is supported by the CICYT (Spain). J.I. and M.L.L. are grateful to the UCM for the 'Beca complutense'. 9 10 P. H. M. de Korte and G. Blasse, J. Solid State Chem., 1982, 44, 150. D. W. Murphy, F. J. Disalvo, J. N. Carides and J. V. Waszcak, Muter. Res. Bull., 1978, 13, 1395. References 11 J. Rodriguez-Carvajal, Program Fullprof, ILL, Grenoble, France, 1990. 1 C. J. Chen, M. Greenblatt, K. Ravindran Nair and J. V. Waszczak, 12 L. J. Van der Pauw, Philips Res. Rep., 1958, 1, 13. 2 J. Solid State Chem., 1989, 81, 64. K. Ravindran Nair and M. Greenblatt, Muter. Res. Bull., 1982, 13 R. D. Shannon, Acta Crystallogr. Sect. A, 1976, 32, 751. 17, 1057. Paper 11026335; Received 3rd June, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910101027

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(6), 1031-1034 Low-temperature Synthesis of YBa,Cu,O,-, Films by the Solution Process using Y-Ba-Cu Heterometallic Alkoxide Shingo Katayama and Masahiro Sekine Colloid Research Institute, 350-1 Ogura, Yahata-higashi-ku, Kitakyushu 805, Japan Superconducting YBa,Cu,O,-, films have been synthesized successfully at a low temperature of 600 "C by the solution process using the Y-Ba-Cu heterometallic alkoxide. The heterometallic alkoxide was synthesized by chemical modification and partial hydrolysis of component alkoxides. In gel films prepared from a heterometallic alkoxide solution, YBa,Cu,O,_, was obtained as a single phase at 600 "C under an argon atmosphere, whereas YBa,Cu,O,-, together with other crystalline phases was obtained from mixed alkoxide solutions.The heterometal- lic alkoxide precursor and the firing process under argon both proved effective for the low-temperature synthesis of single-phase YBa,Cu,O,._, films. The film fired at 800 "C for 6 h under argon followed by annealing at 450 "C for 24 h under oxygen, showed zero resistance at 74 K. Keywords: Oxide superconductor ; Y-Ba-Cu-0 system ; Metal alkoxide precursor Since the discovery of the high-T, superconductivity of YBa,Cu,O, -x,l various preparation processes of YBa2Cu307-x films have been developed for the application to electronic devices and magnetic shields. The solution process is an ideal route for preparing YB~,CU,O,-~ films since shaped ceramics can be made at relatively low tempera- ture, giving pure and homogeneous products, and because of the simplicity of the preparation. Therefore, many efforts have been made to prepare YB~,CU,O,-~ films by the solution process using starting materials such as acetate^,^ organic and metal alk~xides.~-" In particular, metal alkoxides have potential as precursors in the solution process since hydrolysis and condensation of metal alkoxides provide a polymeric precursor processing metalloxiane bonds, by which it should be possible to obtained YBa2C~307-x at low firing temperature. Lowering the synthesis temperature in the fabrication of YBa2Cu,07 -x films helps to avoid reactions of the film with substrates.Most reported solution processes using metal alkoxides for the preparation of YBa2Cu307 -x powders'' and lead to the formation of BaC03, Y203, and CuO as intermedi- ate phases, which react with each other to yield YBa2Cu307 -x.This is similar to conventional solid-state reactions. Therefore the advantages of the solution process have not been evident because the firing temperature is reduced only to 800 "C, although crystalline particles of the intermediate phases pre- pared by the solution process are small and homogeneously mixed with each other. The stability of BaCO, prevents further lowering of the synthesis temperature. The complete reaction of BaCO, requires a heating temperature of 800 "C or more. Only a few reports are currently available on the solution process which avoids the formation of BaCO, and gives YBa2Cu307-x powders at low temperature.Murakami et a/.', reported the synthesis of YB~,CU~O,-~at 650°C by the solution process using Y-butoxide, Ba-ethoxide, and Cu(N03),. However, (NO,)-was introduced into the system, consequently leading to the formation of Ba(NO,), as an intermediate phase. This formation suppresses that of stable BaCO, to yield YB~,CU~O,-~ at low temperature. In the solution process using metal alkoxides as Y, Ba, and Cu metal sources, Hirano et a1." found ozone gas to suppress BaCO, formation effectively during firing and YBa2Cu307 -x films to be obtained at 650 "C. Horowitz et all3 reported that, when an inert atmosphere was used, a powdery precipitate from the hydrolysis of metal alkoxides led to YBa2Cu307-, formation at 650 "C, but with other phases.The authors prepared YBa,Cu,O, -x fibres using Y-Ba- Cu heterometallic alkoxide. l4 This heterometallic alkoxide appeared to be a precursor having component metals in molecules. The use of heterometallic alkoxide should therefore lead to the production of a homogeneous gel film and reduction in the formation temperature of YBa2Cu307 -x. In this study, the firing atmosphere and improvement of the metal alkoxide precursor were examined to find means for obtaining YBa,Cu30, -x films at low temperature. Experimental Y(O-iC3H7),, Ba(OC2H5),, and Cu(OCH,), were used as starting alkoxides (where 0-iC3H7 is the isopropoxy group). Y(O-iC3H7), was commercially obtained (High Purity Chemi- cals).Ba(OC,H,), was synthesized by the addition of 2.4~10~~mol of Ba metal to 50 cm3 of ethanol and the obtained solution was used. Cu(OCH3), was synthesized by reacting CuCl, in methanol with KOCH3.15 Insoluble Y(O-iC3H7), and CU(OCH,)~ were modified so that they would dissolve in a solvent. Y(O-iC3H7), (1.2x lo-, mol) was dissolved in 50 cm3 of 2-methoxyethanol molwith 1.2~10~~of ethyl acetoacetate (EAA) or 3.6 x lop2mol of 2-dimethylaminoethanol. Cu(OCH3), (3.6 x lov2mol) was dissolved in 50 cm3 of 2-methoxyethanol with 7.2 x lo-, mol of ethylenediamine or 2-dimethylamino- ethanol. In modification with 2-dimethylaminoethanol, a sub- stitution reaction of OR groups with the modifier formed M[OCH2CH2N(CH3),],." In a modification with EAA, a substitution reaction of isopropoxy groups in Y(O-iC3H7), gave a chelate compound.14 In a modification with ethylene- diamine, co-ordination to Cu(OCH3), occurred without an OR-substitution reaction to give a chelate compound having methoxy gro~ps.'~ The three alkoxide solutions shown in Table 1 were used to dip-coat films on substrates. The hetero- metallic alkoxide solution A was prepared as follows: Cu(OCH3), modified with ethylenediamine was partially hydrolysed with equimolar water and mixed with Y-alkoxide modified with EAA and Ba-alkoxide solutions. Mixed alkox- ide solutions B and C were prepared as follows: Y(0-iC,H,), modified with EAA, Ba(OC2H5),, and CU(OCH,)~ modified with ethylenediamine were mixed to give an alkoxide solution B.Y(O-iC3H7)3 modified with 2-dimethylaminoethanol, 1032 Table 1 Chemical modifiers used in the experiments solution Y -alkoxide Ba-alkoxide Cu-alkoxide -A" EAAb enc B EAA -en C DMAEd -DMAE a Heterometallic alkoxide solution; ethyl acetoacetate; ethylene-diamine; 2-dimethylaminoethanol. Ba(OC2H5)2, and CU(OCH,)~ modified with 2-dimethylamin- oethanol were mixed to give an alkoxide solution C. Films were formed on partially stabilized Y20,-Zr02 (PSZ) substrates by dip-coating at a draw-up speed of 3 mm s-' in an N2 atmosphere using the three solutions. The size of PSZ substrates used in this experiment was 30 mm x 15 mm x 1 mm. The coated substrates were sub-sequently heated at 200 "C for 5 min in air. This procedure was repeated 15 times so as to increase film thickness.Finally, the films were fired at 500-800 "C for 6 h under argon, after which they were annealed at 450 "C for 24 h under oxygen. The crystal structures of films were examined by X-ray diffraction (Rigaku) using Cu-Ka radiation with a mono-chromator. To determine film morphology, a scanning electron microscope (SEM) was used on JSM-840A (JEOL). Electrical resistance of the films was measured by the conventional four- probe method. Results and Discussion Influence of Firing Atmosphere on Formation of YBa2Cu,0, -x in Films prepared from Heterometallic Alkoxide Solution A Before the firing process, gel films were shown to be amorph- ous by X-ray diffraction. They were fired at various tempera- tures under air or argon to study the formation of YBa2Cu,07 -,.The X-ray diffraction patterns of films fired at 600, 700, and 800 "C for 6 h under air are shown in Fig. 1. Films fired at 600 and 700 "C had BaCO,, Y203, and CuO. In the film fired at 800 "C, YBa2Cu3O7_, was observed as a single phase, as was also noted by the solution process described previously." When fired under air, YBa2Cu,07 -x film is formed at 800 "C through intermediate phases of BaCO,, Y203, and CuO. Although YBa2C~307-x film is formed at a relatively low temperature owing to the fine mixture state of the intermediate phases, the formation of stable BaC0, prevents further lowering of the synthesis 800°Cla a1111 S 600"C S S 30 26i" 40 50 Fig.1 X-Ray diffraction patterns of films fired at 600,700, and 800 "C for 6 h under air. a, YBa,Cu,O,-x; b, BaCO,; c, CuO; s, substrate J. MATER. CHEM., 1991, VOL. 1 temperature. BaC0, may possibly be formed by reaction of Y-Ba-Cu-0 amorphous film with C02 evolved by combus- tion of residual organics presented in films owing to firing in the presence of oxygen. To suppress the evolution of C02and avoid the formation of BaCO,, firing under argon as reported by Horowitz et ~1.'~was conducted. X-Ray diffraction patterns of films fired at 550, 600, and 700 "C for 6 h under argon are shown in Fig. 2. Although X-ray diffraction peaks attributable to BaCO, and CuO were noted for the film fired at 550"C, YBa2Cu307-, precipitated at a temperature as low as 600 "C and crystallinity improved with increase in firing temperature up to 700°C.Firing under argon did not lead to BaC0, formation, as reported.', YBa2C~307-xis thus shown to be obtainable at low temperature. Despite firing under argon, BaCO, was formed at 550 "C. A possible explanation is as follows. In the formation of YBa2Cu,07 -x through the inter- mediate phase of BaCO,, the formation temperature is 800 "C Inor abo~e.~-~*" gel films prepared by this method, YBa2C~307-xwas formed at 800°C or above when firing under air. Consequently, BaCO, in the film fired at 550°C under argon was formed by reaction of the fired film with C02 following removal of the film from the furnace, owing to the high activity. YBa2Cu307-, at 600 "C may thus be formed directly from gel films prepared from heterometallic alkoxide when firing under argon.Influence of Precursors on Formation of YBa2Cu30, -x Firing under inert atmosphere was shown above to be essential to the low-temperature synthesis of YBa2Cu3O7-,from heterometallic alkoxide. To assess the influence of precursors, films were dip-coated on a PSZ substrate using alkoxide solutions A, B, and C, followed by firing at 600 "C for 6 h under argon. Solution A contained heterometallic alkoxide possibly formed as follow^:'^ CU(OCH,),(~~)~+H20+Cu(OCH3)(en)2(OH)+CH30H Cu(OCH,)(en),(OH)+ M(OR), +(CH,0)(en)2Cu-O-M(OR) + ROH here en =ethylenediamine and M = Y(EAA), Ba. The final alkoxide derivative should have the structure of heterometallic alkoxide.Solution B contains mixed alkoxides such as Y-al- koxide modified with EAA, Ba-alkoxide and Cu-alkoxide modified with ethylenediamine. The same chemical modifiers a 600°C In, S 550c -11 I I I I 20 30 40 50 261" Fig. 2 X-Ray diffraction patterns of films fired at 550,600 and 700 "C for 6 h under argon. a, YBa,Cu,O, -x; b, BaCO,; c, CuO; s, substrate J. MATER. CHEM., 1991, VOL. 1 as those of solution A were used. Solution C contains mixed alkoxides such as Y-alkoxide modified with 2-dimethylamino-ethanol, Ba-alkoxide and Cu-alkoxide modified with 2-dimethylaminoethanol. X-Ray diffraction patterns of films prepared from solutions A, B, and C are shown in Fig. 3. In all cases, YBa,Cu,O,-, was formed at 600 "C under argon, but in films prepared from solutions B and C, BaCO, was also observed with YBa2Cu307-x.By firing under inert atmosphere, YBa2Cu,07-x was readily obtained from amorphous films prepared from the metal alkoxide solutions. The homogenous dispersion of Y, Ba, and Cu atoms in the amorphous gel films thus appears possible before firing and homogeneity must be improved by heterometallic alkoxide solution A. Y, Ba, and Cu species are considered to be deposited simultaneously on substrates from heterometallic alkoxide to give homogeneous gel films. In mixed alkoxide solutions B and C, however, slight heterogeneity in gel films is considered to build up owing to differences of hydrolysis rates of metal alkoxides.Although the chemical modifiers of solution A were the same as those of solution B, only solution A having the structure of heterometallic alkoxide gave a single phase of YBa2Cu307-x, thus showing it is possible for heterometallic alkoxide precursors to provide homogeneous gel films. Characterization of YBa2Cu30, -x Films Oxygen deficiency (x) in YBa2Cu307-,influences structural and superconducting properties. In the compo-sition range x~0-0.3gives the so-called ortho-I phase with 90 K T,. In the more oxygen-deficient xzO.3-0.5, the ortho-I1 phase with 60 K T, appears. Above xzO.5, the compound has a tetragonal structure and shows no superconductivity. YBa2Cu3O7_,films fired under argon have high oxygen deficiency and no superconductivity.YBa,Cu,07 -,films prepared using solution A were thus fired under argon, followed by annealing under oxygen to increase the oxygen content. The temperature dependence of electrical resistance for films fired at 600, 700, and 800 "C for 6 h under argon, followed by annealing at 450 "C for 24 h under oxygen, is shown in Fig. 4. Electrical resistance was normalized to resist-ance at 300 K. T,(onset) for the films was ca. 90-95 K. Films fired at 600 and 700°C did not show zero resistance above 40K. That fired at 800 "C showed T,(zero) of 74K. The resistance uersus temperature curve of the film fired at 600 "C showed two drops around 60 and 90 K, possibly correspond-ing to a mixed state of ortho-11 and ortho-I phases.The a I B .I I S Y Rs ;I L I I I 5020 30 261" 40 Fig. 3 X-Ray diffraction patterns of films prepared from solutions A, B, and C, followed by firing at 600°C for 6 h under argon. a,I YBa,Cu,O,-x; b, BaCO,; c, &O; d, Y,O,; s, substrate 1033 I I I 1I 2 Y 0 c2 U--.. h blU 01 I I 0 50 100 150 200 TiK Fig. 4 Temperature dependence of electrical resistance for films fired at (a) 600, (b)700, and (c) 800 "C for 6 h under argon, followed by annealing at 450 "C for 24 h under oxygen. Electrical resistance is normalized to resistance at 300 K Fig. 5 SEM of the morphology of the film fired at (a) 600, (b)700, and (c) 800 "C for 6 h under argon, followed by annealing at 450 "C for 24 h under oxygen transition width decreased with increase in firing temperature.This may possibly have been due to the influence of the degree of crystallization caused by the firing temperature. Fig. 5 shows SEM photographs of the morphology of films fired at (a)600, (b) 700, and (c) 800 "C for 6 h under argon, followed by annealing at 450 "C for 24 h under oxygen. These films had no cracks, and film thickness was ca. 1 pm. In films fired at 600 and 700 "C, grains were too small to be observed. Grain size may have been less than 0.1 pm. In the film fired at 800 "C, they eventually attained submicrometre size. Grain size increased with firing temperature. Using homogeneous gel films prepared from heterometallic alkoxide and firing under argon atmosphere, YBazCu307 -x was possibly formed directly from amorphous gel films and showed high T,(zero) of 74 K in films prepared by the solution process.It is considered that the further improvement of superconducting properties such as T,(zero) and J, requires the investigation of the appropriate combination of firing and annealing conditions. Conclusions YBaZCu3O7-x films were successfully fabricated at low tem- perature by the chemical process using a homogeneous solu- tion of metal alkoxides. (1) When firing under argon, YBa,Cu,O,-, precipitated from gel films at a temperature as low as 600 "C. (2) The heterometallic alkoxide solution gave a more homogeneous gel film than that possible with mixed alkoxide solutions. The gel film was fired at 600 "C under argon to yield YBa2Cu307-x without other phases such as that of BaCO,.(3) The film fired at 800 "C for 6 h under argon, followed by annealing at 450 "C for 24 h under oxygen, exhibited zero resistance at 74 K. The authors thank the Japan Key Technology Center for financial support for 'Research and development ofproduction technology of high performance ceramics with a controlled colloidal solution as a precursor'. Our appreciation is expressed to Miss Akiko Kamimura for her assistance. J. MATER. CHEM., 1991, VOL. 1 References 1 M. K. Wu, J. L. Ashburn, C. J. Torng, P. H. Hor, R. L. Meng, L. Gao, Z. J. Huang, Y. Q. Wang and C. W. Chu Phys. Rev. Lett., 1987, 58, 908. 2 A. Gupta, G. Koren, E. A. Giess, N.R. Moore, E. J. M. O'Sullivan and E. I. Copper, Appl. Phys. Lett., 1988, 52, 163. 3 J. J. Chu, R. S. Liu, J. H. Kung, P. T. Wu and L. J. Chen, J. Appl. Phys., 1988, 64, 2523. 4 C. E. Rice, R. B. van Dover and G. J. Fisanick, Appl. Phys. Lett., 1987, 51, 1842. 5 T. Kumagai, H. Yokota, K. Kawaguchi, W. Kondo and S. Mizuta, Chem. Lett., 1987, 1645. 6 H. Nasu, S. Makida, T. Imura and Y. Osaka, J. Muter. Sci. Lett., 1988, 7, 858. 7 S. Shibata, T. Kitagawa, H. Okazaki, T. Kimura and T. Murak- ami, J. Appl. Phys., 1988, 27, L53. 8 T. Nonaka, K. Kaneko, T. Hasegawa, K. Kishio, Y. Takahashi, K. Kobayashi, K. Kitazawa and K. Fueki, J. Appl. Phys., 1988, 27, L867. 9 T. Monde, H. Kozuka and S. Sakka, Chem. Lett., 1988,287. 10 S. Hirano, T.Hayashi and M. Miura, J. Am. Ceram. Soc., 1990, 73, 885. 11 S. Katayama and M. Sekine, J. Muter. Res., 1990, 5, 683. 12 H. Murakami, S. Yaegashi, J. Nishino, Y. Shiohara and S. Tanaka, J. Appl. Phys., 1990, 29, 2715. 13 H. S. Horowitz, S. J. McLain, A. W. Sleight, J. D. Druliner, P. L. Gai, M. J. VanKavelaar, J. L. Wagner, B. D. Biggs and S. J. Poon, Science, 1989, 243, 66. 14 S. Katayama and M. Sekine, Better Ceramics Through Chemistry ZVMuter. Res. SOC.Proc. 180, ed. B. J. J. Zelinski, C. J. Brinker, D. E. Clark and D. R. Ulrich, Material Research Society, Pittsburgh, 1990, p. 897 15 J. V. Singh, B. P. Baranwal and R. C. Mehrotra, 2. Anorg. Allg. Chem., 1981, 477, 235. 16 A. M. Kini, U. Geiser, H-0. I. Kao, K. D. Carlson, H. H. Wong, M. R. Monaghan and J. M. Williams, Inorg. Chem., 1978, 26, 649. 17 G. Fuchs, A. Gladun, R. Muller, M. Ritschel, G. Krabbers, P. Verges and H. Vinzelberg, J. Less-Common Metals, 1989, 151, 103. 18 H. Mazaki, Y. Ueda, Y. Aihara, T. Kubozoe and K. Kosuge, Jpn. J. Appl. Phys., 1989, 28, L368. Paper 1/02714J; Received 6th June, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910101031

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991,1(6), 1035-1039 Atomistic Lattice Simulations of the Ternary Fluorides AMF, (A=Li, Na, K, Rb, Cs; M=Mg, Ca, Sr, Ba) Neil L. Allan,*' Mark J. Dayer,b Daniel T. Kulpband William C. Mackrodtb a School of Chemistry, University of Bristol, Cantocks Close, Bristol BS8 ITS, UK ICI Chemicals and Polymers Ltd., P.O. Box 8, The Heath, Runcorn, Cheshire WA7 400, UK Atomistic lattice calculations are reported of the structure and stability of the series of ternary inorganic fluorides AMF, (A=Li+, Na+, K+, Rb+, Cs+; M=Mg2+, Ca2+, Sr2+, Ba2+). The predicted low-temperature structures agree with the available experimental data, with good agreement between the experimental and theoretical lattice constants. When A+ and M2+ are comparable in size, low temperature phases with the ferroelectric lithium niobate structure are predicted.As yet no phases with this structure appear to have been observed. Keywords: Atomistic lattice simulation ; Ternary Fluoride Solid inorganic fluorides appear to be playing an increasingly important role in areas such as novel glasses for low-loss optical fibres, solid-state lubricants, thin-film solid electrolytes and lasers,' in addition to their established use as fluorination catalysts, principally in the synthesis of fluorocarbons. In common with other classes of ionic insulators, detailed infor- mation of the lattice and defect properties, many of which control the applications currently being exploited, is sparse, so that the design of new materials from fundamental consider- ations is limited.However, recent theoretical studies, mainly of oxides,2 have shown that many important solid-state properties related to phase stability, stoichiometry, matter and charge transport, impurity segregation and the like can be calculated to within experimental accuracy using atomistic lattice simulations. Furthermore, the structures of inorganic fluorides are commonly close packed and hence generally less complex than those of the corresponding oxides and chlorides, owing presumably to the greater ionicity and reduced size and polarisability of the fluoride ion, which makes their study even more suited to these techniques. However, apart from work, mainly by Catlow and c~-workers,~*~ on the binary alkali-metal and alkaline-earth-metal fluorides, there would seem to be relatively few reports on more complex fluorides, which is surprising in view of the range of complex oxides that have been ~tudied.~Accordingly, this paper reports atomistic lattice calculations of the structure and stability of a range of ternary fluorides of the type AMF,, where A =Li, Na, K, Rb, Cs; M =Mg, Ca, Sr, Ba.Theoretical Methods The theoretical methods used in this study are similar to those used previously for a wide range of ceramic oxides.2 The calculations are all formulated within the framework of an ionic model, which is generally more applicable to fluorides than it is to oxides, with integral charges assigned to the constituent ions, i.e.+I for Li-Cs, +2 for Mg-Ba and -1 for F. Two-body interatomic potentials have been used throughout and are based on a modified form of the Kim- Gordon electron-gas approach.6 As ionic polar- izability was included by means of the Dick-Overhauser shell model.7 Following the approach for complex oxides adopted in recent studies of high-T, ternary cuprates,8 the potentials for A+-F-and M2+-F- were exactly those derived for the binary systems, AF and MF2,9t all of which were based on a single F--F-potential, which has been retained in the present study. The shell parameters for A+, M2+ and F-are retained from the parent binary fluorides. The associated shell-model polarizability of F-is 0.99 A3. The lattice simulations reported are all static simulations of perfect lattices, which give the crystal structure and lattice energy of the low-temperature phase.At 0 K, the lattice structure is determined by the condition that it is in mechan- ical equilibrium i.e. aqaxi=0 in which E is the internal energy, and the (Xi}are the variables that define the structure, namely the three lattice vectors, the atomic positions in the unit cell, and, in the case of the shell model, the shell displacements. The last of these represent the electronic polarization of those ions which are not at a centre of inversion symmetry in the lattice and, for polarizable ions such as Cs+ or F-, can make an appreciable contribution to the internal energy. AMF3 Compounds We have based our study of AMF3 compounds on the most common structures adopted by AMO, oxides," since the oxide and fluoride ions have similar radii under normal conditions of temperature and pressure.These structures fall into two classes. (i) The first arises when A is large enough for the formation of close-packed layers AX3 which can be stacked in various ways. The simplest such structure is the cubic perovskite (Fig. 1) in which the AX3 layers are cubic close packed. Orthorhombic variants, in which the M-X-M bridges linking the MX6 octahedra are not linear, are also common (Fig. 2). Known fluorides with the cubic perovskite structure, which are relevant to the present work, include KMgF,, RbMgF,, RbCaF,, CsCaF, and BaLiF,. In all except the last of these structures it is the larger univalent ion which is 12-co-ordinate with a nearest-neighbour separation of 2-'I2a,, where a, is the lattice constant.The divalent ions are six-co-ordinate with a smaller nearest-neighbour separation of a,/2. In contrast BaLiF, has an 'inverse perovskite' structure in that the large barium ion is 12-co-ordinate and the smaller lithium ion six- co-ordinate. Known orthorhombic perovskites include t Full details of the shell-model parameters and two-body potentials are available from the author*. OF eM (-J*......:. ..I.. Fig. 1 'Ideal' cubic perovskite structure Fig. 2 Tilting of MX, octahedra in orthorhombically distorted AMF, perovskites (after ref. 30) NaMgF,, KCaF, and RbCaF,. Other stacking sequences of the AX, layers are known.In oxides" there is a large number Of possible structures, whereas there appear to be only three types of hexagonal fluoride struct~re.'~-~~ These are the RbNiF,, CsCoF,, and CsNiF, structures (Fig. 3) in which the CsCoF, 0 Co,Ni0Cs,Rb B A €3 J. MATER. CHEM., 1991, VOL. 1 AF3 layers are packed in the order ABCACBA..., ABABCBCACA... and ABA ..., respectively. Oxides with these structures are BaTiO,, BaRuO, and BaNiO,." Of the fluor- ides to be considered here RbMgF, has the RbNiF, struc-ture," while at high pressure CsMgF, exhibits both the RbNiF, and CsCoF, structures.I6 (ii) In oxides the second class of structures occurs when A and M are approximately the same size and the size is suitable for octahedral co-ordination.These adopt structures which are either a random or ordered arrangement of A and M ions both of which are six-co-ordinate. Examples considered in this work are the lithium niobate and ilmenite structures" (Fig. 4), both of which contain hexagonally packed anion layers and differ solely in the distribution of the cations between the octahedral holes. The cation stacking sequence along the c-axis in the LiNbO, structure is LiNbLiNb ... and in the ilmenite structure, LiNbNbLi ... We have been unable to find reports of any ternary fluoride with either type of structure. Indeed, Babel l2 has commented that fluoride struc- tures of the ilmenite type 'do not seem to exist'. Previous attempts to rationalise the structures adopted by 0 Nb 0 Fig.4 Lithium niobate crystal structure. The ilmenite structure is very similar; the stacking sequence of cations A and B along the c axis is ABBA ... in place of ABAB ... CsNiF, RbNiF, A B C A C B A B C A Fig. 3 RbNiF,, CsCoF, and CsNiF, crystal structures (after ref. 13) J. MATER. CHEM., 1991, VOL. 1 ternary systems such as these have been largely in terms of the radii of the constituent ions.12-14 By defining a tolerance factor, t, t =(rA+rX)/2'12(rM+rx) where rA, rM and rx are the ionic radii of ions A, M and X, then the following rules have been pr~posed'~,'~ linking the value of t with the structure of the compound AMX,: 0.76 <t <0.88* orthorhombic perovskite 0.88 <t <1.003 cubic perovskite 1.OO <t <1.1 3 hexagonal perovskite Babel" comments that this very simple idea is much more successful at rationalising the structures of fluoride perovskites than those of the oxide perovskites for which it was originally developed, presumably because of the greater ionicity of the fluorides.In this scheme when t= 1, both cations are in contact with the anion in the 'ideal' cubic structure. For t<0.88, the A cation is too small to touch the anions in the cubic structure and the M-F-M links bend, tilting the MF6 octahedra to bring some anions into contact with the A cations. If t >1, hexagonal structures form in which there is some degree of face sharing of MF6 octahedra (Fig.3). When t is very large, as in CsNiF, (Fig. 3), there is no corner sharing of these octahedra at all. Table 1 lists the values of the tolerance factor t for the systems studied in this work. The ionic radii have been taken from Shannon and Pre~itt,'~ with an effective ionic radius of 1.33 8, for the fluoride ion. For consistency with the work of Babel14 ionic radii for the 12-co-ordinate cations have been assumed to be 6% greater than the radii for the same ions when octahedrally co-ordinated. The values for the tolerance factor t' for the 'inverse perovskite' structure, in which the co- ordinations of the A and M ions are reversed, are given by These are also listed in Table 1. It is clear from Table 1 that there are several combinations of cations of similar size (e.g.Li+ and Mg2+, Na+ and Ca2+, K+ and Ba2+), for which both t and t' are less than 0.76 in which case the rules given above do not apply; it is for these combinations that the corresponding ternary fluorides might be expected to adopt the lithium niobate or ilmenite structures.For each AMF, compound we have calculated the lattice energy and lattice constants of the possible structures: cubic, orthorhombic, hexagonal perovskite, lithium niobate and ilmenite. Triclinic distortions of the orthorhombic structure were also investigated. For each system the predicted low- temperature phase, i.e. that with the lowest lattice energy, is listed in Table 2. For the cubic and orthorhombic perovskites N denotes 'normal' 12-co-ordination of the univalent cation; R ('reversed') denotes octahedral co-ordination of this ion (the inverse perovskite structure).The corresponding lattice con- stants and lattice energies are listed in Tables 3 and 4. It is Table 1 Values of the tolerance factors t and t' for the AMF, systems studied ion MgZ+(0.72) Ca2+(1.00) Sr2+(1.16) Ba"(1.36) Li'(0.74) Na +(1.02)K+(1.38) 0.73/0.7I 0.83/0.63 0.96/0.55 0.64/0.82 0.73/0.72 0.85/0.62 0.60/0.87 0.69/0.77 0.79/0.67 0.56/0.95 0.63/0.83 0.73/0.72 Rb +(1.49) Cs'( 1.70) 1.00j0.52 1.08/0.49 0.88/0.60 0.95/0.56 0.83/0.64 0.89/0.60 0.76/0.69 0.82/0.65 t and t' are defined in the text. The ionic radius in A for the six- co-ordinate cation17 is given in parentheses after each ion.1037 Table 2 Calculated low-temperature phases of AMF, compounds ion Mg2+ Ca2+ Sr2+ Ba2+ Li + LiNbO, OR OR CR" Na+ ON" LiNb0, OR OR K+ CN" ON" LiNbO, LiNbO, Rb+ RbNiF," (H) CN" ON LiNbO, cs + CSN~F,~(H) CN" CN ON ~~~~ C= Cubic perovskite, 0=Orthorhombic perovskite, H =hexagonal perovskite, N =normal (see text: univalent ion is 12-co-ordinate), R = reversed (see text: divalent ion is 12-co-ordinate)." Experimental data are available. In each case the predicted structure is that observed. References to experimental structures are as follows: LiBaF,,26 NaMgF,,I4 KMgF3,27 KCaF,,I4 RbMgF,," RbCaF,,'* CSC~F,.~~ Only high-pressure phases with RbNiF, and CsCoF, structures are known.16 See the text.clear from Table 2 that, where experimental data are available, the predicted structures are those observed at low temperature, while lattice constants are predicted typically to within 1% of the measured values. Attempted synthesis of CaMgF,, under normal pressure conditions, leads only to materials with the composition Cs4Mg,Flo.'* At high pressure16 phases with the RbNiF, and CsCoF, structures are obtained and this is consistent with the well known observation that high pressure stabilizes cubic (relative to hexagonal) stacking of the close-packed layers in these systems. Consequently our prediction of the CsNiF, structure (at zero pressure), with purely hexagonal packing of the CsF, layers, is reasonable, bearing in mind the similar ionic radii of Mg2+ and NiZ+. A comparison of Tables 1 and 2 indicates that predictions of structure simply on the basis of the values oft and tf are remarkably successful.These can be used straightforwardly to predict whether a given perovskite will adopt a normal or inverse structure as well as orthorhombic distortions from the cubic structure. For the orthorhombic perovskites Table 3 also lists the calculated M-F-M bond angles. As a general rule the smaller the value of t (or t),the smaller the M-F-M angle and the larger the orthorhombic distortion. Our conclusions concerning the existence of low-temperature orthorhombic phases for RbCaF, and KCaF,, but not for CsCaF,, agree well with previous static simulation and molecular-dynamics studies.19-22 It is particularly interesting that five of the compounds, in which the univalent and divalent cations are of comparable size (LiMgF,, NaCaF,, KSrF,, KBaF, and RbBaF,), are predicted to adopt the lithium niobate structure. The related ilmenite structure is higher in energy in each case. For these compounds the values of both t and t' are less than 0.77 except for KSrF, where Table 1 suggests an orthorhombic structure. This is the only case where the phase predicted by the calculations differs from that suggested by the tolerance fact or. Although, as already mentioned, no ternary fluoride with the lithium niobate structure seems to have been reported, Edwardson et al. have predicted a low-temperature phase with this structure for NaCaF, on the basis of a molecular- dynamics Lithium niobate is a well known ferroelectric materia1.24,25 Above the Curie temperature the lithium ions move from sites in which they are approximately octahedrally co-ordinated into the nearest anion plane where they are three-fold co- ordinate, while the niobiums move into the centre of the Nb06 octahedra (Fig.4), midway between adjacent anion oxygen planes. For NaCaF,, Edwardson et aLZ3have pre- dicted such displacements of 0.70 and 0.18 A for sodium and J. MATER. CHEM., 1991, VOL. I Table 3 Calculated lattice parameters (in A) for the low-temperature phases listed in Table 2 ion Mgz+ CaZ+ Srz+ BaZ+ ~ ~__________ Li + a =5.028 C= 13.51 a =5.190 b =5.703 a=5.421 b =5.627 a =3.98 l(3.988) c =7.345 c =7.700 e = 146.4 0= 160.5 Na + a= 5.349(5.350) b =5.462(5.474) a =5.764 c = 15.20 a =5.695 b =6.256 a =5.864 b =6.510 c =7.638(7.652)e = 149.7 0 = 134.3 c =8.080 e = 146.4 c =8.359 K+ a =3.989(3.989) a =6.12 l(6.164) a =6.406 a =6.645 b =6.221(6.209) C= 16.30 C= 17.15 c =8.706(8.757) 0 = 152.8 Rbf a =5.838(5.828) a =6.262(6.273) a =6.479 a=6.819 C= 14.21(14.20) b =6.26q6.274) b =6.622 C= 17.32 c =8.881(8.867) c =9.136 e= 167.8 0 = 149.9 cs + a =6.652 a =4.606(4.526) a =4.803 a=7.143 c =5.334 b=7.138 c= 10.12 e= 167.1 ~~ Experimentally known parameters are in parentheses.References to experimental work are as given in Table 2. For the orthorhombic perovskites 0 denotes the calculated MFM bond angle (see text). Table 4 Calculated lattice energies (per formula unit) in eV (kJ mol-') for the low-temperature phase listed in Table 2 ~~~ +ion Mg2+ CaZ Sr2+ BaZ+ +Li -42.00 -38.57 -37.14 -35.77 (-4052) (-3721) (-3584) (-345 1) +Na -40.9 1 -37.19 -35.63 -34.17 (-3947) (-3588) (-3438) (-3297)K+ -39.94 -36.19 -34.48 -32.77 (-3854) (-3492) (-3327) (-3162) Rb+ -39.5 1 -35.93 -34.22 -32.43 (-3812) (-3467) (-3301) (-3 129) cs+ -38.61 -35.05 -33.57 -31.76 (-3725) (-3382) (-3239) (-3064) calcium ions, respectively; the corresponding values reported here are slightly larger at 0.83 and 0.24 A.It is somewhat surprising that there are so few experimental reports of the ternary fluorides studied here.Consequently we have calculated their heat of formation, AH, from the corresponding binary fluorides. These are collected in Table 5. With the exception of KCaF,, for which a small positive heat of formation has been found, the calculated values of AH for the known fluorides LiBaF,, NaMgF,, KMgF,, RbMgF,, RbCaF, and CsCaF, are all negative. Of those that are apparently unknown, the heats of formation of LiMgF, and CsSrF, are calculated to be negative, while LiCaF, has been Table5 Values of AH at OK for the reaction AF(s)+ MF,(s) -,AMF,(s) ion Mg2+ Ca2 SrZ Ba2++ + +Li -0.15 0.10 0.05 -0.17 (-14.5) (9.2) (4.5) (-16.1) Na + -0.2 1 0.32 0.41 0.28 (-19.8) (31.3) (39.7) (26.8)K+ -0.47 0.09 0.33 0.45 (-45.7) (8.5) (3 1.6) (43.0) Rb+ -0.43 -0.04 0.20 0.40 (-4 1.3) (-3.7) (1 9.5) (38.8) +cs -0.47 -0.10 -0.09 0.13 (-45.7) (-9.2) (-8.5) (1 2.5) Units are eV (kJ mol-I).found to have a positive heat of formation comparable to that of KCaF,. The remaining systems, NaCaF,, KSrF, and KBaF,, which are predicted to have the lithium niobate structure, all have large positive heats of formation. As in the case of CsMgF,, which has been referred to previously, attempted synthesis could lead to phases with compositions different from those considered here. Conclusions In this paper we have shown that atomistic simulation tech- niques can be used to model a wide range of ternary fluorides and have examined the structure and stability of the series of compounds AMF, (A=Li, Na, K, Rb, Cs; B=Mg, Ca, Sr, Ba).Where data exist the agreement between experimental and calculated lattice constants is good. The calculations reported here, strictly speaking, refer to 0 K and no estimates of the entropic contribution to the free energy of formation at higher temperature have been made. The fluoride-fluoride potential seems to be widely transferable, probably as a result of the highly ionic character of these systems, and it is intended to use it further in future work. Our results indicate that some AMF, systems, notably those in which the A and M cations are comparable in size, should have a low-temperature phase with the lithium niobate structure. Despite the putative stab- ility of LiMgF, with respect to the binary fluorides, no such fluoride appears to have been reported and it is hoped that an experimental investigation of these compounds might be stimulated by the present work.References Znorganic Solid Fluorides-Chemistry and Physics, ed. P. Hagen-muller, Academic Press, London, 1985. W. C. Mackrodt, Solid State Zonics, 1984, 12, 175. C. R. A. Catlow, ref. 1, ch. 5, and references therein. A. N. Cormack, C. R. A. Catlow and S. Ling, Phys. Rev. B, 1989,40, 3278. S. M. Tomlinson, C. Freeman, C. R. A. Catlow, H. Donnerberg and M. Leslie, J. Chem. SOC., Faraday Trans 2, 1989,85, 367. W. C. Mackrodt and R. F. Stewart, J. Phys. C, 1979, 12, 431. B. G. Dick and A. W. Overhauser, Phys. Rev., 1958, 112, 90. N. L. Allan and W. C. Mackrodt, J.Am. Ceram. SOC., 1990, 73, 3175. J. MATER. CHEM., 1991, VOL. 1 9 N. L. Allan, D. T. Kulp and W. C. Mackrodt, unpublished results. 10 A. F. Wells, Structural Inorganic Chemistry, Oxford University Press, Oxford, 5th edn., 1984. 11 See, e.g. R. W. G. Wyckoff, Crystal Structures, Interscience, New York, 2nd edn., 1963, vol. 2. 12 D. Babel, Struct. Bonding (Berlin), 1967, 3, 1. 13 D. Babel, 2. Anorg. Allg. Chem., 1969, 369, 117. 14 D. Babel and A. Tressaud, Crystal Chemistry of Fluorides, ref I, ch. 3. 15 J. M. Dance, N. Kerkouri and A. Tressaud, Muter. Res. Bull., 1979, 14, 869. 16 J. M. Longo and J. A. Kaflas, J. Solid State Chem., 1969, 1, 103. 17 R. D. Shannon and C. T. Prewitt, Acta Crystallogr., Sect. B, 1969, 25, 925.18 D. Babel, Z. Naturforsch., Teil A, 1965, 20, 165. 19 L. L. Boyer, J. Phys. C, 1984, 17, 1825. 20 L. L. Boyer and J. R. Hardy, Phys. Rev., 1981, 24, 2577. 21 J. W. Flocken, R. A. Guenther, J. R. Hardy and L. L. Boyer, Phys. Rev. Lett., 1986, 56, 1738. 22 S. Nose and M. L. Klein, J. Chem. Phys., 1989, 90,5005. 23 P. J. Edwardson, L. L. Boyer, R. L. Newman, D. H. Fox, J. R. Hardy, J. W. Flocken, R.A. Guenther and W. Mei, Phys. Rev. B, 1989, 13, 9738. 24 M. E. Lines and A. M. Glass, Principles and Applications of Ferroelectrics and Related Materials, Oxford University Press, Oxford, 1977. 25 P. W. Haycock and P. W. Townsend, Appl. Phys. Lett., 1986, 48, 698. 26 W. L. W. Ludekens and A. J. E. Welch, Acta Crystallogr., 1952, 5, 841. 27 R. C. DeVries and R. Roy, J. Am. Chem. SOC., 1953,75, 2459. 28 A Bulou, C. Ridou, M. Rousseau, J. Novet and A. W. Hewat, J. Phys. (Paris), 1980, 41, 87. 29 M. Rousseau, J. Y. Gesland, B. Hennion, G. Heger and B. Renker, Solid State Commun., 1981, 38, 45. 30 J. Geller and E. A. Wood, Acta Crystallogr., 1956, 9, 563. Paper 1/02721B;Received 7th June, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910101035

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(6), 1041-1043 1041 Pressure-sensitive Absorption Spectra of Thin Films of Bis(diphenylglyoximato)platinum(ii), Pt(dpg),: Potential Application as an Indicator of Pressure lchimin Shirotani," Yukio Inagaki," Wataru Utsumib and Takehiko Yagib "Muroran Institute of Technology, 27-1, Mizumoto, Muroran-shi 050, Japan bThe Institute for Solid State Physics, The University of Tokyo, Roppongi, Minato-ku, Tokyo 106, Japan The optical properties of thin films of Pt(dpg), have been studied at high pressures. Two absorption bands of the complex in the visible region shifted sharply to longer wavelengths with increasing pressure. The rates of the red shift with pressure were ca. -1900 cm-' GPa-' for the metal-to-ligand charge-transfer(M-L) band and -3000 cm-' GPa-' for the 5d-6p band.These values are the largest in the known one-dimensional dB metal complexes. The colours of the thin films in the diamond-anvil pressure cell were observed visually at various pressures. The colours of Pt(dpg), turned from red-brown at atmospheric pressure to brown at 0.27 GPa, green at 0.69 GPa, to yellow-green at 1.24 GPa and yellow at 1.92 GPa. This material can be utilized as an indicator of pressure over a GPa range 0-2. Keywords: Optical activity ; High pressure ; Thin film The d8 metal complexes with various kinds of 1,2-dionediox- imes crystallize in a columnar structure. The molecules of these complexes stack one above the other with rotation of 90" which forms a linear chain. Bis( 1,2-dionedioximato)M1' (M =Ni, Pd, Pt) complexes are chemically stable, and have various fine colours at atmospheric pressure.Absorption bands of these complexes show a remarkable shift to longer wavelengths with increasing In addition, a new pressure-induced absorption band is observed for the Pt complexe~.~.~The colours of bis(1,2-dionedioximato)M1' change with the pressure shift of the absorption bands. For example, the colours of the nioxime ligand bis( 1,2-cyclohexane- dionedioximato)Pd", Pd(niox),, turn from yellow through orange, red, purple, blue, to green and pale yellow with increasing pressure.8 If the relationship between colour and pressure is studied in detail, a semiquantitative value of pressure could be obtained from the visual observation of the change in colour with pres~ure.~*~ This can be utilized as an indicator of pressure by a colorimetric method similar to pH testing paper. We have already found a pressure-sensitive platinum com- plex, bis(diphenylglyoximato)platinum(II), Pt(dp&.' A mol-ecular structure of the complex is shown in Fig.l. Evaporated films of bis( 1,2-dionedioximato)M1' complexes are easily pre- pared in UUCUO.~~The optical properties of thin films of Pt(dpg), have been studied at high pressures. This material can be used as an indicator of pressure in the low-pressure region. Fig. 1 Molecular structure of bis(dipheny1glyoximato)M" (M =Ni, Pd, Pt), M(dpgh Experimental The development of diamond-anvil pressure cells enables the effect of the pressure on various materials to be observed in situ.Using this cell, photographs of a thin film of Pt(dpg), were taken at various pressures. The absorption spectra of the complex were measured simultaneously at high pressures. An optical system consisted of a standard microscope and a monochromator with an associated photodetection system. This apparatus is shown in Fig. 2. Pressure was determined from pressure shift in the sharp R-line fluorescence spectrum 1 x-y recorder (6) 35mm camera (9) photon counter (8) photom -17 no 0 iI 0 I (7)spectrometer (3) objectives (5) He-Cd laser diamond cell (4) condenser (1) microscope Fig. 2 Optical system with high pressure apparatus J. MATER.CHEM., 1991, Vol. 1 film 3 -I single crystal .1 !I needle axis I I I I 25 20 15 10 v/103 crn-' Fig. 3 Polarized reflectance spectra of a single crystal of Pt(d~g)~ of ruby." Water was used as the pressure-transmitting medium. Pt(d~g)~was prepared by stirring a mixture of an aqueous solution of K2PtC1, and a hot alcoholic solution of diphenylglyoxime (dpg). The complex was purified by recrys- tallization. The thin films of the complex were prepared by evaporation onto substrates in a vacuum of ca. Torr.t" The thickness of the films was monitored by means of a quart z-crys t a1 oscillator. Results and Discussion The platinum ions in the square-planar d8 complex shown in Fig. 1 are surrounded by four nitrogen atoms of two diphenylglyoxime anions. The d orbitals of the platinum ion are split by a crystal field of symmetry. The eight electrons of the platinum ion core fill the dz2, d,,, d,, and d,, states.Crystalline spectra of bis(dimethylglyoximato)M", M(dmg),, have been studied at atmospheric pressure. l2 Two character- istic bands in the crystalline state are observed in the visible region. The band polarized parallel to a column is ascribed to the nd -(n + 1)p (n=3, 4, 5) transition. On the other hand, the band polarized perpendicular to a column is assigned to the metal-to-ligand charge-transfer (M-L) transition. Fig. 3 shows the polarized reflectance spectra of a single crystal of Pt(dpg),. The 394 nm (25 400 cm-') band was polarized per- pendicular to a needle axis.Thus, the band is ascribed to the M-L transition. The 550 nm (1 8 200 cm-') band was polar- ized parallel to the needle axis. This band is due to the 5d-6p transition. The 394 and 550 nm bands in the film correspond to both bands of the single crystal. Fig.4 shows absorption spectra of the thin film and the CHC13 solution of Pt(dpg)z. The 290 nm band in the film corresponds to 280 nm band in the solution. This band is ascribed to a n-n* transition in the ligand. The d-p band observed in the crystalline spectra was not observed in solution. Fig. 5 shows the absorption spectra of Pt(dpg), at high pressures. The sample was evaporated directly onto the surface of the diamond-anvil in high vacuum. The film thickness was ca.3000A. Absorption spectra of the film were measured t 1 Torr = 133.322 Pa I 2 00 600 800 400 i/nm (-)Fig.4 Absorption spectra of Pt(d~g)~, thin film; (---) CHCI, solution 400 500 600 700 800 A/nm Fig. 5 Absorption spectra of Pr(dpg), thin film at (-) 0, (---) 0.27, (.....) 0.69, (-.-) 1.24, (--) 1.92 GPa over the 0-2 GPa region. The absorption peaks of the M-L and d-p bands shifted sharply to longer wavelengths with increasing pressure. The rates of the red shifts with pressure were -1900cm-' GPa-' for the M-L band and -3000 cm-' GPa-' for the d-p band. These values are the largest in the known one-dimensional d8 metal complexes. High-pressure absorption spectra of the KBr disc of Pt(dpg), have been studied previou~ly.~ The pressure shifts for the thin film are much greater than those for the KBr disc.This tendency is also observed for Pd(ni~x)~. The colours of the film changed markedly with the red shift of the bands at high pressures. We have observed visually the sample in the dia- mond-anvil cell at high pressures. Plate l shows a series of photographs of Pt(dpg), at various pressures. The colours of the complex changed from red-brown at atmospheric pressure through brown at 0.27 GPa, green at 0.69 GPa, yellow-green at 1.24 GPa to yellow at 1.92 GPa. If the relationship between colour and pressure is studied in detail, a semiquantitative value of pressure can be obtained from the visual observation of the change in colour with pressure. This can be utilized as an indicator of pressure.It should be noted that the colour tone depends on a number of factors including light source, sample thickness, pressure-transmitting medium and pressure distribution. Pd(niox), turns from yellow to orange and then to success- ive colours with increasing pressure.8 This complex has an absorption band based on the d-p transition in the visible region. The d-p band shifts from 477 nm at atmospheric pressure to 700 nm at 6 GPa. The rate of the red shift is ca. -1100 cm- GPa-', much smaller than that of Pt(dpg)z. Pd(niox), becomes an excellent pressure indicator over the range 0-8GPa. On the other hand, Pt(d~g)~ has M-L and d-p bands in the visible region. These bands showed very J.MATER. CHEM., 1991, VOL. 1 Plate 1 Pt (dpg), at (a)atmospheric pressure; (b)0.27 GPa; (c) 0.69 GPa; (d) 1.24 GPa; (e) 1.92 GPa (Facing p. 1042)I. Shirotani et al. J. MATER. CHEM., 1991, Vol. 1 large red shifts with pressure. Thus, Pt(dpg), can be utilized as a pressure indicator in the low-pressure region. The crystal structure of Pt(dpg), has not been studied yet at high pressures. However, we have reported previously the results of the crystal structure of Pt(dmg), at high pressures.2 The lattice constants shrink ca. 9% for the c axis (needle axis) and ca. 4.5% for the a and b axes, up to 4GPa. Similar results are expected for Pt(dpg),. The direction of transition for the d-p band is parallel to the needle axis with Pt-Pt bonds. The dZ2 and p orbitals extend to the direction of the needle axis.Thus, the d-p band is very sensitive to pressure. On the other hand, the direction of the transition for the M- L band is perpendicular to the needle axis. The M-L band is the transition from d,, and d,, orbitals in the central metal to the 7c* orbital in the ligand. Since the needle axis of Pt(dpg), is more easily compressed than the other axes, the pressure shift of the d-p band is much greater than that of the M-L band. The pressure shifts of the d-p bands of M(niox),, M(dmg), and M(dpg), are given in Table 1. These are approximate mean values over the range 0-2 Gpa and are very large. The rate of red shift with pressure increases in the order, Ni complexes <Pd complexes, <Pt complexes and in the order (niox) complexes <(dmg) complexes <(dpg) complexes.Thus, the peak shift of Pt(dpg), is the largest in known (1,2-Table 1 Rates of red shift (cm-' GPa-') of the d-p bands of bis(l,2-dionedioximato)M(n) complexes at high pressure M(niox), Ni -820 -840 -1300 Pd -1 130 -1130 -1940 Pt -2400 -2600 -3000 dionedioximato)M" complexes. The crystal packing of M(dpg), is very loose because of the bulky phenyl group. The M-M distances of M(dpg), are greater than those of M(dmg), and M(niox),.13 Thus, the physical properties of M(dpg), are very sensitive to pre~sure.'~ The authors thank Professor M. Tanaka, Nagoya University, for the measurement of polarized reflectance spectra of the single crystal of Pt(dpg),.References 1 L. E. Godycki and R. E. Rundle, Acta Crystallogr., 1953, 6, 487. 2 M. Konno, T. Okamoto and I. Shirotani, Acta Crystallogr., Sect. B., 1988, 45, 142. 3 J. C. Zahner and H. G. Drickamer, J. Chem. Phys., 1960, 33, 1625. 4 M. Tkacz and H. G. Drickamer, J. Chem. Phys., 1986, 85, 1184. 5 Y. Hara, I. Shirotani and A. Onodera, Solid State Commun., 1976, 19, 181. 6 I. Shirotani and T. Suzuki, Solid State Commun., 1986, 59, 533; I. Shirotani, M. Konno and Y. Taniguchi, Synth. Met., 1989, 29, F123. 7 I. Shirotani, A. Kawamura, K. Suzuki, W. Utsumi and T. Yagi, Bull. Chem. SOC. Jpn., 1991, 64, 1607. 8 I. Shirotani, Platinum Met. Rev., 1987, 31, 20. 9 I. Shirotani, Gendai Kagaku, 1987, 191, No 2, 30. 10 I. Shirotani, N. Minobe, Y. Ohotsuki, H. Yamochi and G. Saito, Chem. Phys. Lett., 1988, 147, 231. 11 J. D. Barnett, S. Block and G.J. Piermarini, Rev. Sci. instrum., 1973,44, 1. 12 Y. Ohashi, I. Hanazaki and S. Nagakura, inorg. Chem., 1970, 9, 2551. 13 A. S. Foust and R. H. Soderberg, J. Am. Chem. SOC., 1967, 89, 5507. 14 I. Shirotani, K. Suzuki, T. Suzuki, T. Yagi and M. Tanaka, submitted. Paper 1/02752B; Received 10th June, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910101041

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(6), 1045-1050 Photogenerated Amines and their Use in the Design of a Positive- tone Resist Material based on Electrophilic Aromatic Substitution Stephen Matuszczak,a James F. Cameron,a Jean M. J. Frechet*” and C. Grant Wilsonb a Department of Chemistry, Baker Laboratory, Cornell University, Ithaca, NY 74853-7307, USA IBM Almaden Research Laboratory, San Jose, CA 95720-6099, USA The photogeneration of an active amine within a cationically curable polymer coating can be used to design a novel positive-tone resist material. The resist is based on a copolymer containing 4-hydroxystyrene as well as 4-acetoxymethylstyrene units; when heated in the presence of an acid, this copolymer crosslinks through an electrophilic aromatic substitution process.Therefore, a small amount of 2-nitrobenzyl toluene-p-sulphonate, that decomposes upon heating to produce toluene sulphonic acid, is added to the resist along with a thermally stable but photoactive carbamate that liberates an amine upon irradiation. Exposure of a film of the resist to 254 nm UV radiation results in the formation of a latent image consisting of amine molecules dispersed within the polymer film. The latent image is ‘fixed’ by heating; this liberates acid, which is neutralized where amine has been formed, but causes crosslinking of the polymer by a cationic process in those areas of the film where no amine has been produced. This resist, based on an image-reversal concept applicable to numerous cationically activated resists, can be developed in aqueous base and shows a good sensitivity of ca.19 mJ ern-'. Keywords: Microlithography; Resist; Image reversal ; Photogenerated base The development of highly sensitive resist materials suitable for modern microlithography has proceeded rapidly in recent years with the design of several families of chemically amplified resists.’-3 Perhaps the best known chemically amplified resist to date is based on poly(4-tert-butyloxycarbonyloxystyrene),4 a polymer which is susceptible to acid-catalysed thermolysis of its side-chain tert-butyloxycarbonyl protecting groups in a process that results in a significant change in polarity and solubility. Imaging is achieved through the radiation-induced generation of acid within the polymer film.’-’ This concept has been extended to numerous other functional polymers that are susceptible to acid-catalysed therm~lysis.~.’ More recently, another approach to chemically amplified resists has involved the use of photogenerated acid to crosslink coatings through electrophilic aromatic substitution processes.6-8 This type of reaction is very interesting as it involves a catalytic process that leads to extremely high resist sensitivities.Unfor- tunately, this concept has only been applied successfully to negative-tone resists, since imaging results from crosslinking of the polymer in the exposed areas of the film. In order to extend this mode of imaging to the formation of positive-tone images, we are exploring novel polymer structures that are susceptible to electrophilic aromatic rearrangements.8 The concept of image reversal’ has sometimes been used to change the image tone of a resist material.The best known examples of such processes are the ‘monazoline’, process which is used to produce negative-tone images from the classical novolac-diazonaphthoquinone resists,’ and the gas-phase modification processes that are frequently used in combination with plasma This report describes a simple image-reversal process involving the concept of in situ base photogeneration to effect the local neutralization of an acidic crosslinking catalyst. A preliminary report involving the photogeneration of base to devise a four-component acid- hardening photoresist has appeared.12 Experimental Instrumentations Infrared spectra were recorded using a Nicolet FTIR/44 spectrometer while UV spectra were obtained using a Nicolet UV spectrophotometer. An IBM-Brucker AF 300 spec-trometer operating at 75.4 MHz for 13Cwas used to obtain H and I3C spectra.Gel permeation chromatography was carried out using a Waters 150C gel permeation chromato- graph equipped with a differential refractometer and four PL gel columns of lo6, lo’, lo3 A porosity with tetrahydrofuran as the mobile phase. The molecular-weight data are relative to polystyrene standards. Microanalyses were performed by M.H.W. Laboratories, Phoenix, AZ. Materials Poly(4-acetoxymethylstyrene-co-4-hydroxystyrene), 1, con-taining the two repeating units in a molar ratio of 1 :4 was prepared as described previ~usly~*~ The polymer had M, = 25 000 and M, = 11 000 (GPC with polystyrene standards).The thermally activated acid precursor (TAAP), 2-nitroben- zyl toluene-p-sulphonate, 2, was prepared by the method of Houlihan et a2.13The photochemically activated base precur- sors (PABP) 3-7 were synthesized as reported previou~ly.’~ All materials gave satisfactory elemental analyses and spectra consistent with the proposed structures. 3 4 .No2 J. MATER. CHEM., 1991, VOL. 1 7 Sensitivity Measurements and Imaging Experiments Solutions of 20 wt.% of poly(4-acetoxymethylstyrene-co-4-hydroxystyrene) (1 :4 ratio of repeating units) in 2-methoxy- ethyl ether containing various amounts of 2-nitrobenzyl tolu- ene-p-sulphonate and of the base photoprecursor were prepared.The resulting solutions were filtered through a 0.45 pm Teflon filter and applied to standard silicon, sodium chloride and quartz discs with a Headway Research spin- coater. All films were pre-baked at 80 "C for 1 min. Film thicknesses were measured on a Tencor Sigmascan and were of the order of 0.7 pm. Resist films were irradiated using an Optical Associates exposure system comprising a mercury- xenon lamp with a shutter system, an intensity controller, and an exposure timer. Photon flux was measured using an Optical Associates OAI-3 54 exposure monitor equipped with a 254 nm probe. The lamp output was filtered via a 254 nm narrow bandwidth filter from Oriel Corporation.The light passed through a multidensity resolution filter (Ditrich Optics) in order to produce a range of doses impinging on the resist film. The films were given a post-exposure bake at 120 "C for 1 min to release the acid and effect reaction within the film of copolymer 1. The last step, image development, was achieved by immersion of the films into a stirred solution of aqueous trimethylammonium hydroxide MIF3 12 (Hoechst- Celanese) diluted with water (1 :I) for 130 s, followed by washing with distilled water and air drying. The thickness of the film remaining was measured as a function of the exposure dose received. Film thicknesses were normalized relative to the initial film thickness and plotted against the log of the exposure dose.From these curves, the sensitivity value, Do, and the contrast (slope of the linear portion of the sensitivity curve), y, of each system were determined. Quantitative Infrared Monitoring of the Thermal Generation of Acid A solution of polystyrene in diglyme containing 2-nitrobenzyl toluene-p-sulphonate (5 mol%) was used to cast films of ca. 0.7 pm thickness onto sodium chloride discs. The films were dried at 80°C for 1 min and then subjected to increasing heating periods at 120°C to mimic the post-exposure bake step. By using a Nicolet FTIR/44 spectrometer equipped with software for quantitative analysis, the percentage conversion resulting from each heating cycle was deterrninedI5 by measur- ing the decrease in the asymmetric nitro absorption band at 1530 cm-I relative to the constant intensity C-H defor-mation band at 700 cm-of the polystyrene. Earlier studies have confirmed that the rate of decomposition of 2 upon heating in a variety of polymeric substrates can be measured accurately and in reproducible fashion.' Results and Discussion The overall process to obtain a positive tone image from copolymer 1 that was initially designed to give negative tone images via acid-catalysed crosslinking is shown in Scheme 1.In the first step, the film is irradiated to liberate the base within the polymer matrix. This is followed by application of heat which causes the release of the toluene-p-sulphonic acid from its thermally labile precursor. In the irradiated areas of irradiation photogenerated amine f ifih maskli!JJ1Jlrrrrrlll::I...__.. /\resist -heat c r-7- crosslinked aqueous acid + base positive-tone Scheme 1 the film, the acid is neutralized by the photogenerated base to produce a neutral salt that does not react with copolymer 1.In contrast, acid released in the unirradiated areas of the film catalyses the electrophilic aromatic substitution reaction within 1, which results in crosslinking of the polymer matrix (Scheme 2). Finally, the image is developed using an aqueous base which dissolves the non-crosslinked polymer from exposed areas and affords a non-swollen positive-tone image. Copolymer 1, chosen as the crosslinkable matrix for this study, contains the two repeating units 4-acetoxymethylstyr- ene and 4-hydroxystyrene, in a ratio of 1 :4.This composition was chosen because of its desirable reactivity and solubility properties. It shows a high reactivity, due to the large number of latent electrophilic groups, and it contains enough phenolic units to allow aqueous base development. In addition, this polymer has been studied exten~ively'.~ as a chemically ampli- fied negative resist that is capable of producing high-resolution images well below 0.5 pm in size. The choice of thermally activated acid precursor (TAAP) was governed by the avail- ability of 2. Although a family of interesting thermally labile sulphonium salts has been described recently by Sundell and co-workersl6 the more readily available 2-nitrobenzyl toluene- p-sulphonate was selected.This compound is suitable as a TAAP since it decomposes rapidly'3.'5 at temperatures above its melting point. Scheme 3 outlines the processes involved in the thermal release of acid from 2, as well as in the photochemical release of base from 3 within the resist film. Five different photoactive base precursors were tested, the first three, 3-5, being used to generate cyclohexylamine, and the last two, 6 and 7 being capable of producing 1,6-hexanediamine by exposure to UV light. All five base precursors release carbon dioxide as well as a carbonylated nitrosoarene in addition to the free amine or diamine upon UV irradiation. In order to simplify termin- ology in the case of the diamine precursors, the terms molar OAc crosslinked polymer Scheme 2 J.MATER. CHEM., 1991, VOL. 1 NO2 NO/ \I 2 ,No2 NO 3 Scheme 3 amount or molar ratio will refer to amounts involved in the release of a single equivalent of amino functionality. At first glance, the selection of 2-nitrobenzyl toluene-p- sulphonate as TAAP may appear unusual since this compound is also light sensitive =0.1 1) and its chromophore is similar to that used for one of the base14 photoprecursors (@254=0.13). Exposure to light will therefore result in the release of both acid and base within the exposed areas of the resist, leading to a small reduction in the sensitivity of the overall system if some photons are also consumed in the generation of acid.In practice, this is not a significant problem as the molar ratio of PABP :TAAP (2) is kept relatively high and, therefore, most of the light is in fact absorbed by the base precursor. In order to determine the minimum amount of acid required to crosslink the polymer, different blends containing increasing amounts of 2 as well as thermally stable base precursor such as 3 were tested. Films prepared from these formulations were baked at 80 "C for 1 min, cooled and then baked again at 120 "C for 1 min, thus duplicating the conditions used for the thermal crosslinking reaction. These experiments confirm that films of 1 containing 2 wt.% of 2 become fully crosslinked as a result of this treatment, which mimics that used in the imaging process.Monitoring of the extent of crosslinking was accomplished through film-thickness measurements, no loss of film thickness being observed with the 2% acid precursor formulation upon immersion of the film in aqueous base (undiluted MIF 312) for periods longer than 3 min. Following this study, all resist formulations tested subsequently incorpor- ated 2 wt.% of 2 with respect to copolymer 1. In terms of lithography, an important factor to consider is the UV absorption of the resist films. Values for the absorb- ency per pm of film thickness of the various resist blends used are given in Table 1. The absorbency of the copolymer itself is in the range 0.3-0.4 pm-' (film thickness), a value which is well suited for lithographic applications.However, the relatively high concentrations of PABP required to obtain reasonable sensitivity values lead to a significant increase in the absorption of the films. In addition there is no photo- bleaching of the photoactive compounds upon exposure to 1047 light. Indeed, the products resulting from the 2-nitrobenzyl photorearrangement tend to have a slightly greater absorb- ency than their precursors. To offset this problem of light attenuation, films of lower thicknesses (0.7 pm) were employed. The absorbencies of the various formulations incorporating varying molar ratios PABP :2, with a constant 2 wt.% loading of 2 with respect to the copolymer, are reported in Table 1. Since both the photochemical release of the amine and the thermal liberation of the acid rely on the same type of 2-nitrobenzyl chemistry, it was of interest to attempt to monitor and quantify the overall process by infrared spec- troscopy.The resist films, coated on sodium chloride sub- strates, were treated under the standard imaging conditions of UV exposure at 254 nm, followed by a post-exposure bake at 120 "C, while monitoring the decrease in the nitro absorp- tion band at 1530 cm-'. On increasing UV exposure (254 nm), the asymmetric N-0 stretch of the 2-nitrobenzyl chromo- phore is seen to decrease gradually. As the photoactive base precursor is present in a much higher concentration than the acid precursor 2, this change is primarily the result of the photochemical release of cyclohexylamine.On the other hand, the thermal liberation of acid is not visible by infrared spectroscopy in these imaging formulations since only 2 wt.% of the thermally sensitive 2-nitrobenzyl toluene-p-sulphonate, 2, is present, and the changes that occur during the brief post- exposure bake are too small to be measured. In fact, the thermal decomposition of 2 into toluene-p-sulphonic acid during the baking step can be measured in model studies using 0.7 pm thick films of polystyrene more highly loaded with 2. Monitoring the conversion by quantitative infrared spectroscopy shows that in the typical post-bake period of 1 min at 120 "C only 5% of the available acid precursor 2 is converted into the free acid. As can be seen in Fig.1, this conversion increases with increasing time of post-bake. There- fore, it is not surprising that in the actual resist with only 2% of compound 2, the change in the nitro absorption due to the thermal generation of acid within the resist films cannot be observed. However, if the resist blend is highly loaded with 1.0128 z.I-1.000.-c -7 0.980 2 v 0.960 0 2 0.940.-E 0.920 E 4-11~1111~1111~1111~1111~1111~111 1600 1550 1500 1450 1400 1350 wavenurnber/crn -' Fig. 1 Change in nitro band absorptions upon heating a 0.7 pm thick film of polystyrene doped with 2 at 120°C. (a) Before heating; (b) after 1 min; (c) after 5 min; (d)after 10 min Table 1 UV absorbance per pm of film thickness for resists containing 1, with 2 wt.% of 2 and varying amounts of PABP UV absorbance per pm of film thickness ~ ~~~~~~~ ~~~~ PABP base precursor %4 PABP:2=6: 1 8: 1 12: 1 16: 1 3 0.13 0.74 0.74 0.82 4 0.62 0.76 0.90 1.13 5 0.11 - 0.72 0.82 6' - 0.80 0.95 1.18 7b - - 0.72 0.80 ~~~~~~~~~~~~~ ~ ~~~~~~ From ref.14; for these diamines this molar ratio represents the ratio of latent amino groups to acid groups. 1048 12 wt.% of 2 and 8 molar equivalents of 3, the expected changes in nitro absorption due to both the thermal gener- ation of acid and the photochemical release of amine are readily observable (Fig. 2). Representative positive-tone sensitivity curves obtained for resist formulations containing a cyclohexylamine photoprec- ursor as well as 2 in a ratio of 16: 1 are shown in Fig.3. These curves illustrate that the sensitivity, Do, is strongly dependent upon the nature of the light-sensitive base precur- sor. Table 2 summarizes the resist sensitivity and resist con- trast values that were measured in a series of experiments involving different photoprecursors of amines as well as different molar ratios PABP :2. The resist contrast values are very high, varying from 2.4 to 4.0; although best contrast values are obtained for the simple 2-nitrobenzyl carbamate 3, the differences in contrast between the various amine precur- sors are not significant. Fig.4 illustrates the changes in sensitivity values as a function of the concentration of the photoactive cyclohexylamine precursor.The overall trend is an increase in sensitivity with increasing concentration of the PABP. This effect appears to be most pronounced in the case of 3. The sensitivity of these positive imaging systems is greatly affected by the exact structure of the chromophore used for the cyclohexylamine precursor with compound 5 the most sensitive. The overall order of sensitivity, at each respective concentration, is as follows: 5 >4 >3. The differences in sensitivity between the 2-nitrobenzyloxy carbamate 3 and the related 2,6-dinitrobenzyl carbamate 4 is probably a reflection of their relative photo-efficiencies, 0.13 and 0.62 re~pectively,'~for the photochemical release of c.-t E-0.750 0.7242' I I I I 1 I I I 1 YI I 1 I I I I 1560 1540 1520 1500 1480 wavenumbericm-' Fig.2 Change in the nitro band at 1527 cm-' upon imaging of the photoresist containing 12 wt.% 2 and 8 molar equiv. of 5. (a) Before irradiation; (b) after 20 mJ cm-2; (c) after 40 mJ cmP2; (d) after 60 mJ dm-2; (e) after irradiation as in (d) and heating 1 min at 120 "C 1 J. MATER. CHEM., 1991, VOL. 1 10 100 exposure dose/mJ cm-' Fig. 3 Sensitivity curves for base precursors: a,3; .,4 A,5 cyclohexylamine. In the case of the 2-nitro-a-methylbenzyl- oxycarbonyl-masked cyclohexylamine 5 the quantum efficiency is only 0.1 1, yet the resist sensitivity is highest and this appears to be the most effective PABP for this resist design. This finding suggests that factors other than the quantum efficiency of the PABP are responsible for the ultimate sensitivity (19 mJ cm-2) of the system.This sensitivity value corresponds to an exposure dose (19 mJ cm-2) that is one order of magnitude higher than that required for imaging of the negative-tone resist7 based on the same copolymer 1 and an onium salt. Among other factors, this reflects the lower quantum yield of the overall imaging scheme that requires the photogeneration of an amine in a non-chemically amplified process. An important factor that must be considered is the actual availability of free amine. The 2-nitro-a-methylbenzyl carba- mate 5 is the most effective because the photo by-product that is released upon photolysis is a ketone, 2-nitrosobenzo- phenone (Scheme 4), rather than a nitrosoaldehyde6 as is the case with the other active carbamates 3 and 4.This difference is important since recombination of the photogenerated amine Table 2 Sensitivity and contrast values for different resist compositions base precursor ratioa polymer :2 ratiob PAPB :2 sensitivity D,/mJ cm-2 ~~ contrast, y 3 14.2 8.1 99 4.0 3 12.9 12.0 70 3.2 3 14.3 16.1 54 3.7 4 14.1 8.0 51 3.5 4 14.2 12.0 40 3.2 4 13.9 16.0 35 2.4 5 14.8 5.9 50 2.7 5 13.6 12.0 27 3.1 5 13.6 16.0 19 2.8 6 14.1 8.0 67 3.2 6 14.3 12.2 45 2.7 6 13.5 16.0 36 3.4 7 14.3 12.0 31 2.4 7 14.4 15.8 21 2.8 a Molar ratio of acetoxymethyl groups in polymer 1 to acid precursor 2; molar ratio of amino group precursor to acid precursor 2.Note that for diamines the molecular weight of the precursor is divided by 2 to account for its formation of two amino groups per molecule. J. MATER. CHEM., 1991, VOL. 1 10 15 20 PABP :2 Fig. 4 Changes in sensitivity as a function of loading of base precur-sor. The amount of 2 is constant at 2 wt.% with respect to polymer 1: 0,3; m,4; A,5 NO2 NO '0 5 NO NO / Scheme 4 with this carbonylated by-product to form an imine (Scheme 4) is less likely to occur with the ketonic than with the aldehydic nitroso compound. It must be emphasized that this problem of partial photoproduct recombination is not signifi- cant in most applications of these photoactive carbamates, as our earlier studies have confirmed that, under non-acidic conditions, free amines are indeed produced and little, if any, imine by-products are A problem arises in the specific case of this resist system as acid is also generated in the vicinity of the nitrosocarbonyl and amine photoproducts. Since imine formation is an acid-catalysed process, compe- tition between amine and imine production becomes more significant in the case of compounds 3 or 4 that liberate an aldehydic by-product than is the case with 5.This observation is also supported by earlier work in which low yields of free amino acids were reported for the photochemical deprotection of 2-nitrobenzylcarbamoyl-protected amino acids.I7 There- fore, the 2-nitro-a-methylbenzyl carbamate, despite its rela- tively low quantum efficiency, is the PABP of choice in this application as it affords a significantly greater concentration of free amine with which to neutralize the thermally generated toluene-p-sulphonic acid.Another factor that may play a role in the overall process is the possible photo-dimerization of the nitrosobenzaldehydes by-products of 3 and 4 to azodicarboxylic acids which can then act as efficient internal filters.'* Again, this process, which does not appear to be taking place to a significant extent under the conditions used in this and similar studies,14 is eliminated with 5 since the photo by-product is not an aldehyde. Finally, another potential source of concern is the volatility of the photogenerated cyclohexylamine (b.p.130 "C). Conse- quently, photoprecursors 6 and 7 which liberate the less volatile hexane- 1,6-diamine were also tested. Table 2 also contains the results obtained in resist sensitivity and contrast measurements with these compounds using varying molar ratios of protected amine functionalities and 2. The changes in sensitivity and contrast as a function of the photolabile group and its concentration are similar to those observed for the corresponding cyclohexylamine PABP. Therefore, the volatility of the photogenerated cyclohexylamine is not a significant factor under the conditions used in our imaging experiments. An interesting phenomenon was observed in the amine photoprecursor 7.At higher exposure dose, imaging became increasingly difficult as the film thickness was maintained also in the exposed areas upon development.This problem became acute as the exposure dose was increased further, and full development of the exposed areas to afford a positive image became impossible. The sensitivity curve for this process is shown in Fig. 5. As can be seen in this figure, only a small window exists between 20 and 40 mJ cmP2 for the positive- tone imaging. Doses exceeding 40 mJ cm-2 lead to the forma- tion of an insoluble residue in the exposed areas of the film, as is also the case for exposure doses below 20 mJ cmP2. The exact nature of the reaction leading to this observation is unknown but a possible explanation may lie in the crosslinking of the polymer by the diamine through a yet unconfirmed pathway.No such insolubilization is seen in the case of photogenerated cyclohexylamine. In addition the fact that no crosslinking is observed, even at very high doses, in the case of the 2,6-dinitrobenzyloxycarbonyl-protecteddiamine 6, which is more prone to acid-catalysed imine formation, sug-gests that a high concentration of the free diamine might be required for this crosslinking process to occur. 1 10 100 exposure dose/mJ cm-' Fig. 5 Sensitivity curve with difunctional base precursor 7 1050 J. MATER. CHEM., 1991, VOL. 1 Financial support of this research by the Office of Naval Research and under a gift from IBM Corporation (Materials and Processing Sciences Program) is acknowledged with thanks.8 J. M. J. Frechet, N. Kallman, B. Kryczka, E. Eichler, F. M. Houlihan and C. G. Willson, Polym. Bull., 1988,20,427; H. D. H. Stover, S. Matuszczak, R. Chin, K. Shimizu, C. G. Willson and J. M. J. Frechet, Polym. Muter. Sci. Eng., 1989, 61, 412; J. M. J. Frechet, S. Matuszczak, H. D. H. Stover, B. Reck and C.G. Willson, Polymers in Microlithography, ACS Symp. Ser. 41 2, References 9 C. G. Willson, in Introduction to Microlithography, ed. L. F. 1989, pp. 74-86. C. G. Willson, H. Ito, J. M. J. Frechet, T. G. Tessier and F. M. Houlihan, J. Electrochem. SOC., 1986, 133, 18 1. J. M. J. Frechet, H. Ito and C. G. Willson, Proc. Microcircuit Eng., 1982, 260; C. G. Willson, H. Ito and J.M. J. Frechet, Proc. Microcircuit Eng., 1982, 261. E. Reichmanis, F. M. Houlihan, 0.Nalamasu and T. X. Neenan, Chem. Muter., 1991, 3, 394. J. M. J. Frkchet, E. Eichler, C. G. Willson and H. Ito, Polymer, 1983,24,995; H. Ito, C.G. Willson, J. M. J. Frtchet, M. J. Farrall and E. Eichler, Macromolecules, 1983, 16, 510. J. M. J. Frechet, C. G. Willson, T. Iizawa, T. Nishikubo, K. Igarashi and J. Fahey, Polymers in Microlithography, ACS Symp. Ser. 412, 1989, pp. 100-113; J. M. J. Frechet, E. Eichler, M. Stanciulescu, T. Iizawa, F. Bouchard, F. M. Houlihan and C. G. Willson, in Polymers for High Technology in Electronics and Photonics, ACS Symp. Ser. 346, 1987, pp. 138-148. W. Feely, Proc. SPIE, 1986, 631, 48; R. Dammel, K. F. Dossel, G. Lingnau, J. Theis, H. Huber, H.Oertel and J. Trube, Microelec-tronic Eng., 1989,9,575; A. Bruns, M. Luethje, F. A. Vollenbroek and E. J. Spiertz, Microelectronic Eng., 1987, 6, 467. H. D. H. Stover, S. Matuszczak, C. G. Willson and J. M. J. Fre- 10 11 12 13 14 15 16 17 18 Thompson, C. G. Willson and M. J. Bowden, ACS Advances in Chemistry 2 19, American Chemical Society, Washington D.C., 1983, p. 87 and references therein. J. M. J. Frechet, S. A. MacDonald and C. G. Willson, US. Pat., 4 657 845, 1987. S. A. MacDonald, H. Schlosser, H. Ito, N. J. Clecak and C. G. Willson, Chem. Muter., 1991, 3, 435. W. R. Winkle and K. A. Graziano, J. Photopolym. Sci. Technol., 1990, 3, 4 19. F.M. Houlihan, A. Shugard, R. Gooden and E. Reichmanis, Macromolecules, 1988, 21, 2001. J. F. Cameron and J. M. J. Frkchet, J. Am. Chem. SOC., 1991, 113,4303. J. F. Cameron and J. M. J. Frkchet, Polym. Bull., 1991, 26, 297. P. E. Sundell, PhD. Thesis, Royal Institute of Technology, Stock- holm, Sweden, 1990; H. Jonsson, P. E. Sundell, V. Percec, U. W. Gedde and A. Hult, Polym. Bull., 1991, 25, 649. A. Patchornik, B. Amit and R. B. Woodward, J. Am. Chem. SOC., 1970,92, 6333. V. N. R. Pillai, Synthesis, 1980, 1; W. Reid and M. Wilk, Justus Liebigs Ann. Chem., 1954, 590. chet, Macromolecules, 1991,24, 1741; J. M. J. Frechet, S. Matusz- czak, B. Reck, H.D. H. Stover and C.G. Willson, Macromolecules, 1991, 24, 1746. Paper 1/03059K; Received 20th June, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910101045

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(6), 1051-1056 Synthesis of Aromatic Polyethers by the Scholl Reaction Part 9.t-Cation-Radical Polymerization of 4,4'-Bis(2=naphthoxy)diphenylSulphone Virgil Percec* and James H. Wang Department of Macromolecular Science, Case Western Reserve University, Cleveland, OH 44106-2699, USA The synthesis and cation-radical polymerization of 4,4'-bis(2-naphthyloxy)diphenyl sulphone (3)are presented. For long reaction times, the soluble fractions of the polymers resulting from 3 exhibit a multi-modal molecular- weight distribution consisting of three peaks of very different molecular weights. The highest molecular-weight fraction usually has a number-average molecular weight (Mn)of ca. 106g rn0l-l relative to a polystyrene calibration, while the anof the lowest molecular-weight fraction is usually <10 000 g m0l-l.The multimodal molecular-weight distribution of the polymers synthesized from 3 was suggested to be due to the participation in reactions of several reactive positions on the 2-naphthyloxy rings. The reaction between the most reactive C, positions takes place during the early stage of the polymerization. However, once the concentration of C, positions decreases at a number-average molecular weight of ca. 10 000 g mol-l, intermolecular reactions between the less reactive positions such as C5, C, and C, of the low-molecular-weight polymer chains causes the formation of a branched polymer fraction of very high molecular weight and also a small amount of an insoluble fraction. A polymer fraction of intermediary molecular weight is also obtained.Keywords: Cation-radical polymerization; 4,4'-Bis(2-naphthyloxy)diphenyl sulphone; Aromatic polyether sul-phone ; Scholl reaction Polyether sulphones and pol yether ketones are conventionally synthesized by variants of aromatic nucleophilic substitution or aromatic electrophilic substitution reaction^.'^^ Two novel approaches to the synthesis of these functional aromatic pol yethers have been demonstrated by cation-radical poly-merization of bis(ary1oxy) derivatives by the Scholl reac-tion 10-18 and by the homocoupling of aryl halides by Nio- catalysed reaction^.'^.^^ The cation-radical polymerization of bis(4-phenoxyphenyl) sulphone, 4,4'-bis(pheny1thio)diphenyl sulphone, and bis(4-phenoxyphenyl) sulphone substituted with various electron-donating groups leads to pol yether sulphones of low molecular weight only." This is caused by the low poly- merizability of these monomers.The polymerization of 13-bis(phen0xy)pentanes substituted with methyl groups is also accompanied by proton-transfer reactions from the benzylic groups." The cation-radical polymerization of bis( 1 -naph- thyloxy) monomers leads to high-molecular-weight polymers when the monomers are bisC4-( l-naphthyl- ox y)phen y1] sulphone,' 4,4- bis( 1-naphth ylox y)benzophenone,' a,o-bis[4-( 1-naphthyloxyphenylsulphonyl]perfluoroalkane~,~~ bis[4-( l-naphthyl~xy)phenyl]methane,'~ 1,3-and 1,4-bis[4-( 1 -naphthyl~xy)phenylmethyl]benzene,'~ 2,2'-and 3,3'-bis(1-naphthylo~y)biphenyl,~~ 1,3-bis( 1 -naphthyloxy) benzene,15 and cc,o-bis(l-naphthyloxy)alkanes.12,21The bis( 1 -naphthyloxy) monomers investigated so far are summarized in Scheme 1.This article describes the synthesis and the cation-radical polymerization of the first member from the series of bis(2- naphthyloxy) monomers, i.e. bis[4-(2-naphthyloxy)phenyl] sulphone. Experimental Materials 2-Naphthol (1) (99%, Aldrich), FeCl, (anhydrous, Aldrich), and K2Co3 (Fisher) were used as received. Bis(4-chlorophenyl) p Part 8. V. Percec, J. H. Wang and Y. Oishi, J. Polym. Sci., Polym. Chem. Ed., in the press. sulphone (2, 98%, Aldrich) was recrystallized from toluene. Dimethyl sulphoxide (DMSO, Fisher) was distilled from CaO.Nitrobenzene (PhN02, Fisher) was distilled from CaH, under nitrogen. Other solvents were used as received. Techniques 200MHz 'H NMR spectra were recorded on a Varian XL- 200 spectrometer. All spectra were recorded in CDC1, with TMS as internal standard. Gel permeation chromatography (GPC) measurements were performed on a Perkin-Elmer series 10 LC instrument equipped with an LC-100 column oven, an LC 600 autosampler, and a Nelson Analytical 900 series data station. The measurements were made using a UV detector set at 254 nm, chloroform as solvent (1 ml min-', 40"C), a set of PL-gel columns (500 and 1048,), and a calibration plot constructed with polystyrene standards (Sup- elco). Purity was similarly determined by high-performance liquid chromatography (HPLC)/GPC using a 100 8, PL-gel column.A Perkin-Elmer DSC-4 differential scanning calor- imeter equipped with a TADS 3600 data station was used to determine the glass-transition temperatures of the polymers at a heating rate of 20 "C min-'. The glass-transition tempera- tures were read at the middle of the change in the heat capacity of the second heating scan. Synthesis of 3 2-Naphthol (20.00 g, 138.7 mmol) was dissolved in a mixture of 200 cm3 dry dimethyl sulphoxide and 67 cm3 dry toluene. K2C03 (23.00 g, 166.4 mmol) was added subsequently. The reaction flask was equipped with a nitrogen inlet, a ther-mometer, and a Dean-Stark trap equipped with a condenser. The reaction mixture was heated at 155 "C until no more water was collected in the Dean-Stark trap.Then the mixture was allowed to cool to 70 "C, and bis(4-chlorophenyl) sul- phone (18.33 g, 63.8 mmol) was added. The reaction mixture was stirred at 155 "C for 6 h. The cooled reaction mixture was poured into 2 dm3 cold water, and extracted with chloro- form three times (200 cm3 each). Chloroform was evaporated Ar= +SO2+ Scheme 1 Structure of bis( 1 -naphthyloxy) monomers polymerized by cation-radical reactions on a rotary evaporator. The resulting solid was dissolved in 100 cm3 toluene, washed five times with 2 mol dm-, aqueous NaOH, and then with water until neutral, and subsequently dried over anhydrous MgS04. The evaporation of toluene led to a light-red solid. The solid was purified twice by column chromatography (basic alumina, methylene chloride).Methyl- J. MATER. CHEM., 1991, VOL. 1 ene chloride was evaporated on a rotary evaporator and the resulting residue crystallized when left to stand, yielding 19.97g (62%) of 3. Purity (HPLC), 99.6%; m.p. 134-135 "C; 'H NMR (CDCI,, TMS): dH, 7.07 (d, 4 H, Ph-H meta to the SOz group), 7.21 (dd, 2 H, 1-H of the naphthalene unit), 7.44- 7.52 (m, 6 H, 3-, 6-, 8-H of the naphthalene unit), 7.75 (m, 2 H, 4-H of the naphthalene unit), 7.86-7.96 (m, 8 H, Ph-H ortho to SOz group and 5-and 7-H of the naphthalene unit). Polymerization Experiments All polymerizations were performed under nitrogen in dry nitrobenzene, using FeC1, as oxidant. The detailed polymeriz- ation conditions are summarized in Table 1.A typical poly- merization example is provided below. Compound 3 (0.45 g, 1.0 mmol) was dissolved in 1.0 cm3 dry nitrobenzene placed in a 25 cm3 three-necked flask equipped with a nitrogen inlet-outlet, and an addition funnel. A solution of 0.65 g FeC1, dissolved in 2.5 cm3 dry nitroben- zene was added dropwise under a stream of nitrogen over a 20 min period. The reaction mixture was stirred at 60 "C for 24 h. The content was precipitated into 200 cm3 methanol acidified with 2% HC1. The precipitate was filtered and washed with boiling methanol and dried in uacuo yielding 0.49 g (98%) of polymer. The polymer contains some insoluble fraction. The GPC chromatogram of the soluble fraction of the polymer displayed two peaks.The first peak represents 7% of total area: &fn=0.9 x lo6 g mol-', Mw&fn=3.4. The second peak represents 93% of total area; fin=4200 g mol-', &fw/&fn=2.9.In several cases the progress of the polymeriz- ation reaction was monitored by GPC as described below for experiment 7 from Table 1. After 5, 30, 60, 300 and 1020min, using a syringe fitted with a loin? needle and previously flushed with nitrogen, a sample of 0.1 cm3 of the polymerization mixture was with- drawn and subsequently precipitated into 2.0 cm3 methanol. The separated precipitate was washed twice with methanol. Methanol was evaporated and the resulting precipitate was dried in uacuo. The dried precipitate was analysed by GPC. Results and Discussion The synthesis of 3 is shown in Scheme2.It consists of the aromatic nucleophilic substitution of bis(4-chlorophenyl) sul- phone (2) by 2-naphthol (1). The cation-radical polymerization of 3 is presented in eqn. (2) from Scheme 3. The polymerization reactions were performed in nitrobenzene and were initiated by FeCl, oxi- dant. The expected structure of the repeating structural unit is shown as 4. The results of the polymerization experiments are summarized in Table 1. The most prominent character of the soluble fractions of t 1 in=2.54 cm. w 1 Scheme 2 Synthesis of 3 J. MATER. CHEM., 1991, VOL. 1 Table 1 Polymerization of 3; polymerization time =24 h ~~~ ~ monomer solution FeCl, solution polymer reaction experiment monomer/ temperature/ yield" M,bl no.mmol PhN02/cm3 FeCl,/mmol PhN02/cm3 "C (YO) g mol-' Mw/Mnb T,/ "C ~ ~ ~~ 1 1.o 1 .o 4.0 2.5 25 86 27 x lo6 1.1 (6%) - 7 100 -' (94%) 2 1.o I .o 4.0 2.5 60 98 0.9 x lo6 3.4 (7%) 233 4200 2.9 (93%) 3 1 .o 1.o 4.0 1.5 25 93 19 x lo6 1.2 (4%) 259 7700 -' (96%) 4 I .o 2.0 4.0 2.5 25 70 21 x lo6 1.2 (10%) - 7500 -' (go0/,) 5 1.o 2.0 4.0 4.0 25 71 18 x lo6 1.2 (6%) 274 9000 -' (94%) 6 1 .o 4.0 4.0 2.5 25 58 16 x lo6 1.3 (12%) 274 8700 -' (88%) 7 1.o 0.8 4.0 2.5 60 95 3.8 x lo6 2.3 (42%) - 3700 1.8 (58%) 8 1.o 2.0 4.0 2.5 60 93 20 x lo6 1.2 (7%) 0.9x lo6 1.8 (3%) - 5000 1.7 (goo/,) 9 1.o 1.o 4.0 2.5 100 99 64 x lo6 1.9 (8%) 2.3 x lo6 2.0 (2%) - 4300 1.7 (goo/,) " The polymer yield includes both the soluble and the insoluble fractions.The a,,and M,/M, were determiend from the soluble fraction. Multi-peak molecular weight distributions were observed on the gel permeation chromatograms. The a,and Mw/M, values were calculated and listed for the individual peaks. 'The peak overlapped with a minor peak. 3 L -In 4 Scheme 3 Cation-radical polymerization of 3 the polymers is their multi-modal molecular weight distri- bution. The polymer produced with long reaction times usually has one peak of very high molecular weight (Mn>l x lo6 g mol- '), a peak of intermediary molecular weight, and a low-molecular-weight peak (I@, <10 000 g mol-'). The a,, MW/M,and the area of the individual peaks are listed in Table 1.The GPC traces of several representative polymers derived from 3 are presented in Fig. 1. These polymers were synthe- sized under different experimental conditions. Curve (a) rep-resents the polymer (experiment 1, Table 1) synthesized at room temperature. The main peak has an M,value of 7100 g mol-'. It represents 94% of the total area. The minor peak (6% of total area) has an M, value of 27 x lo6 g mol-' and Mw/Kf,of 1.1 relative to polystyrene standards. Curve (b) displays the GPC trace of a polymer synthesized at the identical monomer and FeCl, concentrations but at an elev- ated temperature (60 "C, experiment 2, Table 1). The polydis- persity of the main peak is broadened.Curves (c) and (d) are I I I I5 10 15 20 elution volurne/cm3 Fig. 1 GPC traces of polymers synthesized from 3 under different reaction conditions: (a)experiment 1; (b)experiment 2; (c) experiment 4; (d)experiment 6; (e)experiment 7 (all from Table 1) the GPC traces of polymers synthesized at lower monomer concentrations. The highest percentage of the high-molecular- weight fraction was observed in curve (e), which has 42% of the high-molecular-weight fraction with M, of 3.8 x lo6 g ' mol-'. Besides the easily distinguishable peaks, the GPC traces shown in Fig. 1 also exhibit a shoulder located between the two major peaks. An example of a polymer with three distinguishable peaks on their GPC traces is shown in Fig. 2 (experiment 8, Table 1).The three peaks have calculated values of relative M, of 20 x lo6, 0.9 x lo6 and 5000 g mol- ',respectively. The ratio of the areas of these three peaks is 7 :3 :90. In order to observe the time sequence of the formation of the individual peaks of different molecular weights, the pro- gress of the polymerization was followed by taking samples I I I I5 10 15 20 elution volurne/cm3 Fig. 2 GPC trace of polymer derived from 3 (experiment 8, Table 1) at different reaction times. The GPC analysis of these collected samples provides the molecular-weight distribution of the polymers. An example is presented in Fig. 3 for the samples taken from experiment 7 (Table 1). Curve (a) displays the molecular-weight distribution of the sample taken at 5 min of polymerization. The polymer consists mostly of oligomers.There is no trace of high-molecular-weight fraction detectable by GPC. As the polymerization continues, the sample taken at 30 min (b)has a multi-modal molecular-weight distribution containing three main peaks. The polymer contains a fraction of broad low molecular weight, a fraction of very high molecular weight and a shoulder of intermediate molecular weight. The subsequent GPC traces are shown in (c)and (d) for t =300 and 1020 min. The molecular weight distributions of the peaks obtained at longer reaction times [(c) and (d)] are very similar to those obtained at 30 min (b)except for the decrease in the amount of oligomers. This indicates that the ~~I I I 10 15 20 elution volume/crn3 Fig.3 GPC traces of polymer samples taken at different reaction times, t/min: (a)5; (b)30; (c) 300, (d) 1020 (experiment 7, Table 1) J.MATER. CHEM., 1991, VOL. 1 resulting polymers change their molecular-weight distri-butions negligibly with the reaction time. The glass-transition temperatures of the polymers synthe- sized from 3, range from 233 to 274°C. The transition temperatures are influenced by the molecular weight and the molecular-weight distribution of the polymer samples. The 200 MHz 'H NMR spectrum of a representative poly- mer derived from 3 is presented in Fig. 4. The assignment of the resonances was based on the expected structural unit 4 (Scheme 3). In spite of the presence of polymers of totally different molecular weights, i.e.the high- and low-molecular- weight fractions, no differentiation can be made based on the 'H NMR spectra for the clear assignment due to each fraction. This is expected since the resonances of high-molecular-weight fraction should be low owing to their low concentration in the polymers (typically <lo%, Table 1). Consequently, the resonances resulting from the high-molecular-weight fraction probably overlap with those from the major resonances resulting from the low-molecular-weight fraction. The multi-modal molecular-weight distribution of the poly- mers synthesized from 3 is most probably due to the presence of several reactive positions in the 2-naphthyloxy ring of the monomer. These reactive positions have different reactivities and concentrations, and consequently may react to a different extent at different stages of the polymerization generating three independent polymeric species. The relative reactivity of the different ring positions of 2-methylnaphthalene cation radical was studied in nucleo- philic substitution reactions using cyanide anions.22 The iso- lated substitution product ratios are summarized in structure 5 in Scheme 4.This suggests the following order of reactivity: C1& C8zC5>C4.These positional reactivities were rational- ized by the molecular-orbital calculations.The electron density IQ ICHCI3 7.26 (c1 7.21-7.39\ I 6 Fig. 4 'HNMR spectrum (CDCl,, TMS, 200 MHz) of a representative polymer derived from 3 7% 60% 0.151 0.197mCH3 6% 4% 0.143 0.159 5 6 Scheme 4 Substitution products distribution and LUMO electron density of 2-methylnaphthalene J.MATER. CHEM., 1991, VOL. 1 1055 of the lowest occupied molecular orbital (LUMO)of 2-methyl- naphthalene cation radical is summarized as structure 6 in (3) Scheme 4.It was proposed that the nucleophilic attack took place preferably at the ring positions with high LUMO electron density. However, the positive charge distribution of 3 7 the 2-methylnaphthalene cation radical did not explain the observed relative reactivity.22 The C1 position is also the most Ar = reactive position on the 2-substituted naphthalene ring in the aromatic electrophilic substitution reactions.', Based on these results, we assume that the C1 position represents the most reactive position of 3 in the cation-radical polymerization.This assumption is supported by the fact that 1,l '-binaphthyL2,2'-diol is the predominant product from the oxidative dimerization of 2-naphth01.~~~~~ 7+3 The mechanism of the cation-radical polymerization of 3 is presented in Scheme 5. The single-electron transfer oxi- dation of monomer 3 by FeC1, oxidant leads to the monomeric cation radical 7, eqn. (3). The radical-substrate ~o~pling~~~~~ between the cation radical 7 and monomer 3 generates the 8 dimeric cation radical 8 eqn. (4). There are three possible pathways for the formation of neutral dimer The first pathway is shown in eqn.(S) and (6), and consists of the single-electron transfer between the dimeric and the mono- meric cation radicals, eqn.(9,leading to the dimeric dication 9, eqn.(S), followed by the subsequent elimination of two 8+7 +3 protons, eqn. (6). The second pathway refers to the oxidation of the dimeric cation-radical 8 by FeC13 oxidant to form the dication 9, eqn. (7). The first step of the third pathway is the elimination of one proton from the dimeric cation radical 8, 9 yielding a dimeric radical 11, eqn. (8). The dimeric radical 11 is subsequently oxidized to its cation 12 by FeCl,, eqn. (9). The single-proton elimination from 12 leads to the neutral dimer 10, eqn. 10. Owing to the high reactivity of the C1 position, the reaction 9 sequence shown in Scheme S occurs at the early stage of the polymerization. However, once the concentration of the C1 position of the 2-naphthyloxy rings is decreased corresponding to a number-average molecular weight of ca.10 000 g mol- (Fig. 3), competitive reactions can occur. 10 The low-molecular-weight polymer chains can undergo intermolecular reactions at the less reactive positions such as C5,C, and C4 which are now available in much higher 8 Fe3 9 concentrations than the position C1. An example for such a reaction is presented in Scheme 6 for the intermolecular dimerization between two C, positions. These intermolecular reactions can lead to soluble branched polymer fractions of very high molecular weight. The narrow polydispersity of the 8 -H+ highest molecular-weight fraction (Table 1) indicates the branched nature of this polymer fraction. The reactions between extensively branched soluble polymer fractions gener- ate the insoluble three-dimensional polymer network.A very low amount of insoluble polymer fraction was present in all 11 polymers that resulted from 3. At low concentrations of C1 groups cyclization reactions are also possible. Conclusions The C1 position of 3 is the most reactive position of 3. 11 (9) Therefore, the cation-radical polymerization of 3 takes place by dehydrogenative C1-Cl coupling of 3. However, once the concentration of C1 functional groups decreases at a number-average molecular weight of ca. 10 000 g mol-' the intermolecular reactions of the less reactive positions such as the C5, C, and C4 carbons of the naphthalene rings of the 12 4' - 12 10 low-molecular-weight polymer chains lead to a soluble frac- Scheme 5 Mechanism of the cation-radical polymerization of 3 tion of branched polymers of molecular weight of ca.lo6 g mol-These branched reactions generate a small concen- tration of insoluble polymer fraction. 1056 J. MATER. CHEM., 1991, VOL. I 3 J. B. Rose, in Recent Advances in Mechanistic and Synthetic Aspects of Polymerization, ed. M. Fontanille and A. Guyot, 2 -Ar 4 Reidel, Dordrecht, 1987, p. 207. R. May, in Encyclopedia of Polymer Science and Engineering, ed. H. F. Mark, N. M. Bikales, C. G. Overberger and G.Menges, 5 Wiley, New York, 2nd edn., 1988, vol. 12, p. 313. J. E. Harris and R. N. Johnson, in Encyclopedia of Polymer Science and Engineering, ed. H. F. Mark, N. M. Bikales, C. G. Overberger and G.Menges, Wiley, New York, 2nd edn., 1988, 13 6 vol. 13, p. 196. P. A. Staniland, in Comprehensive Polymer Science, ed. G. Allen 2 FeCS -2 FeC12, -2 CI-, -2 H+ 1 7 8 9 and J. C. Bevington, Pergamon, Oxford, 1989, vol. 5, p. 483. F. Parodi, in Comprehensive Polymer Science, ed. G. Allen and J. C. Bevington, Pergamon, Oxford, 1989, vol. 5, p. 561. Y. Imai and Y. Oishi, Prog. Polym. Sci., 1989, 14, 173. V. Percec, J. H. Wang and R. S. Clough, Makromol. Chem., Macromol. Symp., in the press. 10 V. Percec and H. Nava, J. Polym. Sci., Polym.Chem. Ed., 1988, 26, 783. I1 V. Percec, J. H. Wang and Y. Oishi, J. Polym. Sci., Polym. Chem. Ed., 1991, 29, 949. 12 V. Percec and J. H. Wang, Polym. Bull., 1991, 25, 9. 13 V. Percec and J. H. Wang, Y. Oishi and A. E. Feiring, J. Polym. Sci., Polym. Chem. Ed., 1991, 29, 965. (11) 14 V. Percec, J. H. Wang and S. Okita, J. Polym. Sci., Polym. Chem. Ed., 1991, 29, 000. 15 16 V. Percec, S. Okita and J. H. Wang, Macromolecules, submitted. V. Percec, J. H. Wang and S. Okita, J. Polym. Sci., Polym. Chem. Ed., submitted. 17 18 V. Percec and J. H. Wang, Makromol. Chem., Macromol. Symp., in the press. V. Percec, J. H. Wang and Y. Oishi, J. Polym. Sci., Polym. Chem. Ed., submitted. 19 I. Colon and G. T. Kwiatkowski, J. Polym. Sci., Polym. Chem. 14 20 Ed., 1990, 28, 367. M. Ueda and F. Ichikawa, Macromolecules, 1990, 23, 926. Scheme 6 The formation of branched polymers during the cation- radical polymerization of 3 Acknowledgment is made to Amoco Performance Products 21 22 23 R. G. Feasy, A. Turner-Jones, P. C. Daffurn and J. L. Freeman, Polymer, 1973, 14, 241. K. Yoshida and S. Nagase, J. Am. Chem. SOC., 1979, 101,4268. P. H. Gore, A. S. Siddiquei and S.Thorburn, J. Chem. SOC., Perkin Trans., 1972, 1, 1781. for financial support of this research. References 24 9.zLJ 26 27 H. Musso, Angew. Chem., 1963,75, 965. M. Tisler, Org. Prep. Proc. Znt., 1986, 18, 19. V. D. Parker, Ado. Phys. Org. Chem., 1983, 19, 131. 0. Hammerich and V. D. Parker, Adv. Phys. Org. Chem., 1983, 1 2 S. Maiti and B. K. Mandal, Prog. Polym. Sci., 1986, 12, 111. M. J. Mullins and E. P. Woo, J. Macromol. Sci.-Rev. Macromol. 20, 55. Chem. Phys., 1987, C27, 313. Paper 11032475; Received 1st July, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910101051

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(6), 1057-1059 Studies of Non-linear Optical Organic Materials: Crystal and Molecular Structure of 2-Dicyanomethylene-l,3-dioxolane Parthasarathi Dastidar, Tayur N. Guru ROW*and Kailasam Venkatesan Department of Organic Chemistry, Indian Institute of Science, Bangalore-560 012, India The structure of 2-dicyanomethylene-1 ,Sdioxolane has been determined from X-ray diffraction data. The compound crystallizes in the chiral space group Cc and has two molecules in the asymmetric unit. The correlation between the molecular packing and the second-harmonic generation (SHG) is discussed. Keywords: X-Ray Diffraction; Non-linear optical material; Second-harmonic generation The search for new organic materials with non-linear efficiency surpassing those existing has been pursued extensively in recent years.' As part of a research programme on developing good non-linear optical materials and to gain insight into the relation between the macroscopic non-linear susceptibility x(2) and the molecular packing in the unit ell,^-^ the crystal structure of the title compound has been determined.The necessary conditions to be satisfied for showing SHG are: (i) the space group must be non-centrosymmetric, (ii) the differ- ence between the ground-state dipole moment and the excited dipole moment should be large and (iii) the molecule should have loosely bound electrons that can be displaced by an optical field. Experimental The title compound was prepared by the reaction of tetra- cyanoethene and ethylene glycol in the presence of urea.5 A pale-yellow, needle-shaped crystal formed by slow evapor- ation of an alcohol-water solution, with dimensions 1.0 mm x 0.5 mm x 0.5 mm was used for X-ray diffraction measurements. Preliminary Weissenberg photographs showed it to be a C-centred monoclinic system.The lattice parameters were refined by using 25 reflections with 20<8/"<40 from graphite-monochromated Cu-Ka radiation (A= 1.5418 A) on a Nonius CAD-4 diffractometer. Intensity data of the 1252 reflections were collected at 293 K in the 01/28 scan mode with 8 between 0 and 60". Three standard reflections (1 T 4, T 3 2, 2 0 6) were monitored after every 100 reflections and showed no significant decomposition or movement of the crystal. Corrections were made for Lorentz effects and polariz- ation but not for absorption effects.The structure was solved by direct methods (SHELX86).6 The best E-map gave all non- hydrogen atoms of both the molecules in the asymmetric unit. Full matrix least-squares refinements (SHELX76)7 were per- formed for positional parameters and anisotropic thermal parameters. All the hydrogen atoms were located by a differ- ence Fourier map. However, they were not refined but their contributions to the structure-factor calculation were con- sidered. The final R and R, were 0.037 and 0.045, respectively, for 1105 significant reflections [IF,[ 2 34 lFol)];the weighting scheme was w = 1.0/[a2(lFoI)+0.0017 lF,12]. The atomic scat- tering factors were taken from ref.8. Calculations were performed on a DEC1090 computer. Results and Discussions The C(2)=C(3) and C(2')=C(3') distances [1.369(4) and 1.356(4) A, respectively] are longer than that of the C=C bond in ethene [1.336(2) A].9 There is a corresponding reduction in the length of donor C,,2-0 and acceptor Csp2-CSp bonds: O(1)-C(3), 0(2)-C(3), O(l')-C(3'), 0(2')-C(3') distances are 1.299(3), 1.309(4), 1.309(4) and 1.313(4) A,respectively, and are shorter than the distance [1.354(16) A] reported for the C,,Z-O bond." On the acceptor side, the distances C( 1)-C(2), C(6)-C(2), C(1')-C(2') and C(6')-C(2') are 1.406(5), 1.409(6), 1.420(4) and 1.404(5) A, shorter than the distance of 1.431(14) A reported for Csp2-CSp bond." These values show that delocalization of IT electrons occurs in the title molecule.The contribution of the microscopic hyperpolarizability to macro- scopic non-linear susceptibility f2) depends on the packing of the molecules in the crystalline state. From the nature of the approximate molecular symmetry, namely mm2 with the two-fold axis coinciding with the ethenic C(2)=C(3) bond, it is reasonable to assume that the charge-transfer axis coincides with this ethenic bond. The angle between the crystallographic b axis and the charge-transfer axis for both the molecules in the asymmetric unit is 28.4" and differs significantly from the theoretically expected value of 54.7" for optimal molecular orientation and phase-matching configuration for the point group m." Furthermore, the charge-transfer axes for both the molecules in the asymmetric unit make an angle of 6 1.7"with the crystallographic mirror plane.As this value is relatively close to 90" it is not beneficial for constructive addition of the molecular hyperpolarizability (p) to the macroscopic second-order electronic susceptibility f2) because reflection about the mirror plane would cancel the molecular hyperpola- rizability. We observe that the molecular packing is unfavour- able for SHG efficiency. The second-harmonic generation for one sample of a powdered specimen of the title compound is only twice that of urea,I2 although with a different powdered sample the value was as low as half that of urea.13 This highlights the limitation of the powder SHG method.The low SHG efficiency could be partly due to the strength of the donor and acceptor groups at the vicinal carbons of the ethenic bond being not so good as discussed earlier. It is obvious that although in both the molecules the observed C=C bond length is significantly larger than that of ethene, these distances are not as large as in other push-pull ethenes with -NMe2 and -C02Me as donor and acceptor groups substituted at the vicinal carbon atom^.'^.'^ However, we have no knowledge of the value of the difference between the ground-state dipole moment and excited-state dipole moment of the title molecule upon which the magnitude of the second- order molecular hyperpolarizability depends.'' It seems clear from the above discussions that the low SHG efficiency arises from the unfavourable molecular packing and perhaps to a lesser degree on the poor donor and acceptor strength. Note that the occurrence of two molecules in the asymmetric unit in this crystal is by no means conducive for achieving good SHG. An interesting question is whether the SHG efficiency would be larger if there were only one molecule in the asymmetric unit. It is reasonable to expect the SHG to be larger with one molecule in the asymmetric unit, but the practical realization of achieving it presents the problem of crystal engineering, central to the design of good non-linear optical materials. Crystal Data C6H4N202, M = 136.0, monoclinic, a =5.288( 1) A, b = 15.044( 1) A, c = 16.356( 1) A, fl= 99.23( 1)’.I/= 1284.4(2) A3 space group Cc, 2=8, pc= 1.406 g cm -3, p(Cu-Ka, A = 1.54 18 A)=8.33 cm-’. The final atomic coordinates with their estimated standard deviations are given in Table 1. The numbering scheme is shown in Fig. 1 and the packing of the molecules viewed Fig. 1 ORTEP plot of a single molecule of title compound with numbering scheme. The other molecule in the asymmetric unit is numbered in the same way Table 1 The fractional atomic coordinates (x lo4) of non-hydrogen atoms of the title compound with their e.s.d.s in parentheses atom X Y z 2248 5788(1) 3527 -229(5) 6443(1) 4302(1) 11 l(7) 41 32(2) 3716(2) -595( 7) 4896(2) 4121(2) 477(6) 5701(2) 3988(2) 2935(8) 6723(2) 3508(3) 1234(8) 7 I 7 l(2) 4007(2) -2476(8) 4827(2) 4638(2)631(9) 3523(2) 3356(2) -4020(9) 4761(3) 5053(2) 1399l(5) 6712(1) 701 l(1) I0734(5) 6056(1) 6231(1) 11670(8) 8 362( 2) 6826( 2) 1053 7( 7) 7596(2) 641 l(2) 11741(6) 6802(2) 6549(2) 14707(7) 5778( 2) 7024( 3) 12476(8) 5322(2) 6528(2) 8 159( 8) 7672(2) 5893(2) 12555(9) 8976(2) 7 172(2) 6 194(8) 7742(3) 5486(2) J.MATER. CHEM., 1991, VOL. 1 7 Fig. 2 Packing of the molecule of the title compound in the unit cell viewed down the a axis Table 2 Bond distances and angles involving non-hydrogen atoms of the title compound with their e.s.d.s in parentheses atoms distance/A atoms distance/A molecule I molecule I1 O(1)-C(3) 1.299(3) O(1’)-C( 3’) 1.309(4) 0(1)-C(4) 1.455(3) O(I ’)-C(4‘) 1.456(3) 0(2)-C(3) 1.308(4) O(2’)- C( 3’) 1.313(4)w-C(5) 1.466(4) O(2’)-C(5’) I .469(4) C(1)-C(2) 1.406(4) C( l‘)-C(2’) 1.420(5) C(11-N 1) 1.146(5) C( 1’)-N(1‘) 1.144(5) CW-C(3) I .369(4) C( 2’) -C( 3’) 1.356(4) C(2)-C(6) I .409(5) C(2’)-C(6‘) 1.404(5) C(4)- (35) 1.471(6) C(4)-C(5’) 1.488(5) C(6)--N(2) 1.147(6) C(6)- N( 2’) 1.146(6) atoms angle/” atoms angle/” molecule I molecule I1 C(3)-O( I)-C(4) 108.4(2) C(3’)-O( l’)-C(4) 108.5(2) C( 3)-O( 2) -C(5) 108.1(2) C( 3’)- O(2’)-C(5’) 108.6(2) C(2)-C(l)-N(l) 177.2(4) C(2’)-C(l’)-N(l’) 178.6(4) C(I)-C(2)-C(3) 120.0(3) C( lF)-C(2‘)-C(3’) 119.0(3) C(l)-C(2)--C(6) 119.3(3) C( l’)-C(2’)-C(6) 119.4(3) C( 3)-C(2) -C(6) 120.7( 3) C(3’)-C(2’)- C(6’) 12 1.6( 3) O(I)-C(3)-0(2) 114.7(3) O(l’)-C(3’)-0(2’) 114.4(3) O(1)-C(3)-C(2) 122.5(3) O(I’)-C(3‘)-C(2’) 123.1(3)O(2)- C( 3)- C( 2) 122.8(3) O(2’)-C( 3’)-C(2’) 122.5( 3) O(1)-C(4)-C( 5) 104.7( 3) O(1’)-C(4)-C(5’) 104.8( 3) 0(2)-C( 5)-C(4) 104.0(3) O(2’)- C( 5’)-C(4) 10333) C( 2)- C( 6)-N( 2) 179.1 (4) C( 2’) -C( 6’) -N( 2) 178.4(4) down the a axis is shown in Fig.2. Bond distances and angles appear in Table 2.7- There are two independent molecules in the asymmetric unit. Both the molecules have similar conformations. The five- membered ring in both the molecules is in an envelope form. The deviation of C(5) in molecule I from the plane containing C(3), 0(1), O(2) and C(4) is 0.035(3) A and that of C(5’) in molecule I1 from the corresponding plane is 0.053(3) A.The deviation of C(2) [0.016(3) A] from a plane defined by C(1), C(3), C(6) and that of C(2’) [0.016(3) A] from a plane defined by C( 1’), C(3’), C(6’) indicates slight pyramidality. Deviations of atoms N(l) and N(2) from the least-squares plane defined by C(1), C(2), C(3) and C(6) are 0.071(3) and 0.025(3) A, respectively, and those of N(1’) and N(2’) from the plane defined by C(l’), C(2’), C(3’) and C(6’) are equal [0.045(3)A]. We also observe non-linearity in C-CN groups (Table 2).169” There are intermolecular short contacts between N and C involving both the independent molecules: C(4) N(l)= 3.089 8, and C(4) -.* N( 1’) =3.090 A, but C-H .-.N hydrogen bonds ?Supplementary data available from the Cambridge Crystallo- graphic Data Centre: see Information for Authors, J.Muter. Chem., 1991, Issue 1 or 4. J. MATER. CHEM., 1991, VOL. 1 1059 are not observed. If we accept 3.4 A as the van der Waals distances for C N with no acid-base character,I8 then the observed C N contacts indicate a fairly strong acid-base interaction. It is found that angles 0(1)-C(4) ... N(1) and O(1’)-C(4’) -.. N(1’) are ca. 166” whereas C(5)-C(4) N(l)and C(5’)-C(4’) ... N(1’) are ca. 89”. Furthermore, the devi- 4 5 6 7 D. Kanagapushpam, K. Venkatesan and T. S. Cameron, Acta Crystallogr., Sect C, 1988, 44,337. W. J. Middleton and V. A. Englehardt, J. Am. Chem. SOC., 1958, 80, 2788. G. M. Sheldrick, SHELX86, program for crystal structure solu- tion, Gottingen University, Germany. G. M. Sheldrick, SHELX76, program for crystal structure deter- ations of N(l) and N(1’)from the planes C(5), C(4), O(1) and C(5’), C(4’), O(1’) are 0.27 and 0.24 A.The calculated values indicate that the observed short C N contacts could be due to intermolecular interaction between the nitrogen lone pair and the C-0 (o*)antibonding orbital. 8 9 10 mination, University of Cambridge. International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. IV, pp. 202-207. L. S. Bartell, E. A. Roth, C. D. Hollowell, K. Kuchitsu and J. E. Young Jr., J. Chem. Phys., 1965,4, 2683. F. H. Allen, 0. Kennard, D. G. Watson, L. Brammer, A. G. Orpen and R. Taylor, J. Chem. SOC., Perkin Trans. 2, 1987, 1. We thank Drs. D. F. Eaton and Y. Wang, Du Pont, Willming- ton, for SHG measurements and the University Grant com- 11 12 J.Zyss and J. L. Oudar, Phys. Rev. A, 1982,4, 2028. J. F. Nicoud and R. J. Twieg, in Nonlinear Optical Properties of Organic Molecules and Crystals, ed. D. S. Chemla and J. Zyss, mission and Council of Scientific and Industrial Research, India for financial support. 13 14 Academic Press, New York, 1987, vol. 2. D. F. Eaton and Y. Wang, personal communication. D. Kanagapushpam and K. Venkatesan, Acta Crystallogr., Sect. C, 1988, 44,337. References 15 D. Adhikesavalu, Nirupa U. Kamath and K. Venkatesan., Proc. Indian Acad. Sci. (Chem. Sci.), 1983, 92, 449. 16 N. Ramasubbu, J. Rajaram and K. Venkatesan, Acta Crystallogr., 1 Non-linear Optical Properties of Organic and Polymeric Materials, Sect. B, 1982, 38, 196. ed. D. J. Williams, ACS Symp. Ser., American Chemical Society, 17 D. A. Mathews, J. Swanson, M. H. Mueller and G. D. Stucky, Washington D.C., 1983. J. Am. Chem. SOC., 1971,93, 5945. 2 D. Kanagapushpam and K. Venkatesan, Acta Crystallogr., Sect. 18 J. R. Witt, D. Britton and C. Mahon, Acta Crystallogr., Sect. B, C, 1987,43, 1597. 1972, 28, 950. 3 D. Kanagapushpam, K. Padmanabhan and K. Venkatesan, Acta Crystallogr., Sect. C, 1987, 43, 1717. Paper 1/03268B; Received 1st July, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910101057

出版商:RSC    

年代:1991

数据来源: RSC