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. 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