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. 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