Synthesis and Characterisation of Side-Chain Liquid Crystalline Poly[1-({[(4-cyano-40- biphenyl)oxy]alkyl}oxy)-2,3-epoxypropane] Xiangen Han, Robert A. Shanks,* Dumitru Pavela School of Applied Science, RMIT University, GPO Box 2476V, Melbourne, Victoria 3001, Australia Fax: 613 9639 1321; E-mail:
[email protected] Received: October 17, 2003; Revised: February 10, 2004; Accepted: February 12, 2004; DOI: 10.1002/macp.200300144 Keywords: liquid-crystalline polymers (LCP); nematic phase; thermal properties Introduction Since the first introduction of side-chain liquid-crystal polymers (SCLCP) by Finkelmann and coworkers in 1978,[1] SCLCPs continue to be the focus of much research interest. This arises not only as a result of their properties as materials in a range of advanced electro-optical technolo- gies,[2–10] but also because they present a demanding challenge to our understanding of self-assembly in molecular systems.[11–13] The main reason is that SCLCPs can combine the unique properties of low-molarmass liquid crystals and polymers, which made it easier to form films duringmaterial processing. The side chain liquid crystalline polymer comprises three structural units: a polymer back- bone, a flexible spacer, and a mesogenic unit. Ringsdorf et al.[14] have discovered that a flexible spacer should be Summary: A new series of side-chain liquid-crystal poly- mers, the poly[1-({[(4-cyano-40-biphenyl)oxy]alkyl}oxy)- 2,3-epoxypropane], has been synthesized in which the spacer length is varied from 2 to 8 methylene units. The synthesis used for the chemical modification of polyepichlorohydrin (PECH) involved the phase transfer catalyzed etherification of the chloromethyl groups with sodium 4-cyano-40-biphen- oxide and lithium n-(4-cyano-40-oxybiphenyl)-alkanoates. All the resulting polymers (except polymers 7 and 8), including that without spacer, characterized by 1HNMR, and IR, exhibit thermotropic liquid crystalline mesomophism. The thermal behavior of the polymers has been characterized using differential scanning calorimetry (DSC) and polarized light microscopy (POM) equipped with hot-stage. A more pronounced odd-even effect in the clearing temperatures is observed on increasing the spacer length in which the odd members display slightly higher values, which were also de- pendent on the substitution degree of PECH. The flexible PECH chain assists nematic LC formation compared with othermore rigid backbone polymers where a smectic phase is often encountered with the same mesogen. A comparison of the thermal properties of the cyanobiphenyl based series reported here. Polyacrylate (PA) and poly(methacrylate)- based (PMA) SCLCPs containing 4-cyanobiphenyl as the mesogenic unit are consistent with the general rule that incre- asing backbone flexibility for a given mesogenic unit and spacer length enhance the clearing temperature. This was not found from the PECH-based series, which show the lower clearing temperature than the PMA and PA series, even though they have more flexible backbone than PA and PMA series. So the clearing temperature is not solely determined by the flexibility of the backbone. Schlieren textures of PECHOC2-B taken at 110 8C (cooling from isotropic phase after annealing 1 h). Macromol. Chem. Phys. 2004, 205, 743–751 DOI: 10.1002/macp.200300144 � 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Full Paper 743 a Current address: National Research Council of Canada, Ottawa, Canada. inserted between the polymer backbone and the mesogenic side group to separate the motion of the polymer backbone. This plays a critical role in determining the properties of the polymer, and to some extent, the relative tendencies of the mesogenic groups to self-assemble from those of the polymer (especially with a rigid) backbone to adopt a random coil configuration. This finding made it possible to synthesize SCLCPs systematically. After this discovery, there have been many systematic studies on the effects of the spacer length on the thermal and physical properties of these SCLCPs.[15–32] It has been shown that increasing the spacer length while keeping the backbone and mesogenic groups constant has two effects: (i) the clearing temperature of the polymer increases and (ii) the entropy change associated with the clearing transition decreases. Most of the research work refers to polyacrylate,[33,34] polymethy- lacrylate,[35,36] polyurethane,[37] and polystyrene[38–41] backbones. There has been only a limited number of research on the polyepichlorohydrin-based SCLCPs polymers.[42,43] In our previous paper[44] we have studied the effect of the mesogenic group on the thermal and physical properties of copolymers. This article reports on the synthesis and characterization of a series of side chain liquid crystal polyepichlorohydrin (PECHOCn-B) prepared by phase transfer chemical modification of polymers. In this paper, we report how the thermotropic properties of copolymers containing cyanophenyl group were affected by alkylene spacers of different lengths, we have now synthesized the poly[1-({[(4-cyano-40-biphenyl)oxy]alkyl}oxy)-2,3-epox- ypropane] (see Figure 1) by chemical modification. The acronym PECHOCn-B is used to refer to these polymers in which n denotes the number of methylene units in the spacer. The length of the spacer has been varied from 2 to 6 methylene units, and we believe that this is the first series of polyepichlorohydrin-based side-group liquid crystal poly- mers to be reported. 4-cyanobiphenyl was chosen as the mesogenic unit because it is the most widely used meso- genic unit and has been attached to a wide range of backbone types. Polyepichlorohydrin (PECH), chosen as the polymer backbone has labile chlorines that facilitate nucleophilic substitution for side-chain modification, and the more important is that it has a flexible backbone. The cyanobiphenyl group can be substituted to PECH via a spacer group to form a SCLCPs. Liquid crystal polymer characteristics are dependent on the spacer group length and structure in addition to the specific mesogenic unit. Both of the above factors allow to compare the effect of backbone flexibility on the thermal and liquid crystal properties. Experimental Part Techniques Nuclear magnetic resonance (NMR) spectra were recorded at room temperature on a Varian Gemini-200 spectrometer using CDCl3 as the solvent. Calculation of the degree of substitution of PECH has been described previously.[45] Thermal char- acterization was made by differential scanning calorimetric (DSC) on a Perkin Elmer Pyris1 instrument. The samples were heated and subsequently cooled in the range between 25 and 150 8C heating and cooling rates were 10 8C �min�1. After the first heating cycle, the samples were held at 150 8C for 5min to obtain identical thermal histories for all polymers before the second cooling/heating cycle. Melting temperature (Tm) was Figure 1. Structures of the polyacrylate (PA), polymethacrylate (PMA) and polyepi- chlorohydrin-based side-chain liquid crystal copolymers (n¼ 2–6). 744 X. Han, R. A. Shanks, D. Pavel Macromol. Chem. Phys. 2004, 205, 743–751 www.mcp-journal.de � 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim measured at the middle of the change in the heat capacity. Polarizing optical microscopy (POM) was used to observe the thermal behaviour properties or the texture of the mesophases. A Nikon Labophot 2 optical microscopy equipped with a Mettler FP-82 hot stage and CCD-IRIS colour video camera was used to observe the thermal transitions and to analyse the anisotropic textures, and Nikon digital camerawas also used to capture images. Materials Polyepichlorohydrin (Aldrich, Mn¼ 700 000 g �mol�1) was purified by precipitation with methanol from chloroform solution. 1H NMR (CDCl3, d, ppm): 3.7 (s, –CH2O, –CH–, –CH2Cl). 4-Hydroxy-4 0-cyanobiphenyl, tetrabutylammonium hydrogen sulfate (TBAH) and butyl lithium (10 mol �L�1 solution in hexane), n-bromo(chloro)-1-alkanol (98%), other reagents were used without further purification,N,N-dimethyl- formamide (DMF) (all from Aldrich) was treated with pota- ssium hydroxide, then dried by azeotropic distillation with benzene and distilled under reduced pressure. Synthesis of Mesogenic Compounds, n-[40-Cyano-4-biphenyly)oxy]alkan-1-ol (n¼ 2–8) The synthesis of n-(4-cyano-40-oxybiphenyl)-alkanoates is outlined in Figure 2. The first step consisted of nucleophilic displacement of the halide of n-haloalkan-1-ol with 4-cyano- 40-hydroxybiphenyl. All the mesogenic compounds were syn- thesized according the literature procedure.[1] Results are reported in Table 1 and Table 2. Synthesis of 4-Cyano-40-[2-hydroxyethyl)oxy]biphenyl (HOC2-B) 4-Cyano-40-hydroxybiphenyl (1.09 g, 0.0056 mol) and potas- sium carbonate (2.65 g, 0.017 mol) were added to acetone (40 ml). 2-Bromoethanol (1.39 g, 0.01 mol) was added to the resulting solution, which was heated to reflux for 24 h. The reaction mixture was poured into diluted HCl solution, and the precipitated product was extracted with chloroform. The combined chloroform extracts were washed with water and dried over anhydrous MgSO4, MgSO4 was removed by filtra- tion and the resultant solution was concentrated in vacuum to give crude crystals that were recrystallized from methanol, yielding 1.70 g (71%), Tm 91.3 8C; Tn-I 102.0 8C (DSC) 1H NMR (CDCl3): d¼ 4.1 (m, PhOCH2, 2H), 4.0 (m, 2H, CH2OH), 6.8–7.5 (m, 8H, aromatic). IR (KBr): 2 223 (CN), 3 296 cm�1 (OH). Synthesis of Poly[1-({[(4-cyano-40-biphenyl)oxy]alkyl}oxy)- 2,3-epoxypropane] The salt of the mesogenic compounds (HOCn-B) were prepa- red by exchange reaction in dry hexane containing butyl lithium at �20 8C. Solvent was removed from the reaction system under reduced pressure and the salt was used directly without further purification. 0.7 g of PECH was dissolved in DMF (50 mL) and lithium 4-cyano-40-[2-hydroxyethanyl)oxy]-biphenyl (1.15 g) and TBAH (0.4 g) were added. The reaction mixture was stirred at 60 8C under a dry nitrogen stream for 192 h. The latter was centrifuged in order to remove lithium chloride and then poured into methanol. The polymers obtained were purified by precipitation from CHCl3 into methanol and finally dried in vacuum at 40 8C for 48 h. The results of the modification of PECHOCn-B are summarized in Table 3, which demonstrates the 15 to 91% sub- stitution of the chloromethyl groups was to be obtained. As determined previously[44] it is necessary to use elevated tem- perature (60 8C) to achieve halide displacement of these weakly electrophilic primary chlorides. The substitution of the chloromethyl groups decreased with increase in spacer length, which had a large effect on their thermal properties. Figure 2. Reaction scheme for the synthesis of monomers and copolymers. Synthesis and Characterisation of Side-Chain Liquid Crystalline Poly[1-({[(4-cyano-40-biphenyl)oxy]alkyl}oxy)-2,3-epoxypropane] 745 Macromol. Chem. Phys. 2004, 205, 743–751 www.mcp-journal.de � 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim IR spectra gave a first indication for the esterification reac- tion between PECHand themesogenic compound according to the reaction shown on Figure 2. Figure 3 presents the IR spectra of reactants, and copolymer PECHOC3-B. Absorption bands due to the 4-Cyano-40-hydroxybiphenyl moieties appeared at the range 2 231 cm�1 (C N stretching vibration) and at 1 714 cm�1 (phenylene ring stretching vibration), respectively, in the IR spectra of PECH. NMR analysis of the starting PECH and HOCn-B com- pounds, andof thePECHOCn-Bproducts confirmed the attach- ment of the synthesizedmesogenic compounds onto the PECH backbone through ester linkage in agreement with reaction shown in Figure 2. In the 1HNMRspectrum of PECHOCn-B in Figure 4, the 1H NMR resonance of saturated hydrocarbon groups exhibited at d¼ 1.0–2.0 and �3.7 ppm (m, H, – O(CH2)nO–, spacer group) and d¼ 3.9–4.3 ppm (5H, polymer backbone), and phenylene rings at d¼ 6.95 ppm (2H) and 7.4– 7.8 ppm (6H,m). These results for IR andNMRspectroscopy in PECHOCn-B demonstrate that monomers n-[40-cyano-4- biphenylyloxy]alkan-1-ol quantitatively reacts with the chlor- omethyl group in polyepichlorohydrin. Figure 4 is given as an example for monomer (HOC3-B), polymer (PECH) and copolymer’s (PECH-OC3-B) NMR graph. The new peaks appearing in Figure 4 at d¼ 1–2, �3.7 ppm, which belong to the spacer group, clearly show that the mesogenic group successfully attached to the polymer backbone. Results and Discussion The thermal behaviours of all synthesized monomers are shown in Table 2. All monomers reveal an enantiotropic nematic phase. When the spacer effect was considered, it was that themelting temperature decreased gradually as the spacer length increased (n value). Figure 5 and 6 display a representative DSC curves of monomer HOC4-B and its polarized microscopy image respectively. In the DSC heating scan, it shows a melting transition at 85.5 8C and a nematic to isotropic phase transition at 107.5 8C. The Table 1. Yield and NMR and IR data of synthesized monomers. Comp. Yield 1H NMR data (d, CDCl3) of monomers IR data (n) % cm�1 HOC2-B 71.1 4.1 (m, PhOCH2, 2H), 4.0 (m, 2H, CH2OH), 6.8–7.5 (m, 8H, aromatic) 2 223 (CN) 3 296 (OH) HOC3-B 71.1 3.65 (t, 2H, CH2OH) 1.94 (m, 2H–CH2–), 6.75–7.60 (m, 8H, aromatic), 3.9 (t, 2H, OCH2) 2 224 (CN) 3 284 (OH) HOC4-B 70.1 1.01–1.95 (m, 4H, –(CH2)2–), 3.65 (t, 2H, –CH2OH) 3.95 (m, PhOCH2, 2H), 6.9–7.66 (m, 8H, aromatic) 2 224 (CN) 3 284 (OH) HOC5-B 70.2 1.05–1.95 (m, 6 H, –(CH2)3–), 3.51 (t, 2H, –CH2OH), 4.0 (m, PhOCH2, 2H), 6.9–7.8 (m, 8H, aromatic) 2 221 (CN) 3 291 (OH) HOC6-B 70.1 1.05–1.95 (m, 8H, –(CH2)4–), 3.65 (t, 2H, –OCH2OH) 4.1 (m, PhOCH2, 2H), 6.9–7.66 (m, 8H, aromatic) 2 223 (CN) 3 296 (OH) HOC7-B 60.4 1.01–1.95 (m, 10H, –(CH2)5–), 3.65 (t, 2H, –OCH2OH), 4.1 (m, PhOCH2, 2H), 6.9–7.66 (m, 8H, aromatic) 2 220 (CN) 3 287 (OH) HOC8-B 60.3 1.01–1.95 (m, 12H, –(CH2)6–), 3.45 (t, 2H, –OCH2OH), 3.96 (m, PhOCH2, 2H), 6.9–7.66 (m, 8H, aromatic) 2 228 (CN) 3 294 (OH) Table 2. Thermal transitions and thermodynamic parameters of monomers HOC2 to HOC6-B. Monomers Phase Transition Temperatures (corresponding enthalpy change) 8C (J � g�1) Heatinga) Cooling HOC2-B K91.3 N102.0(1.25)I K58 N97.6(4.37)I HOC3-B K89 N101.6(4.50)I K72.3 N100.1(4.52)I HOC4-B K85.5 N107.5(3.45)I K71.5 N106.6(3.58)I HOC5-B K84.5 N93.9(3.08)I K65.1 N92.8(4.42)I HOC6-B K81.7 N109.3(0.73)I K42.5 N(1.42)I a) K¼Crystalline, N¼ nematic, I¼ isotropic. Figure 3. IR spectra of PECH (a), PECHOC3-B (b) and mesogenic compound HOC3-B (c). 746 X. Han, R. A. Shanks, D. Pavel Macromol. Chem. Phys. 2004, 205, 743–751 www.mcp-journal.de � 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim cooling scan shows very similar phase behaviour, except that the crystallization temperature was supercooled 15 8C. Table 3 summarizes the phase transitions of polymers PECHOC2-B to PECHOC6-B. All polymers except poly- mer 7 and 8 reveal nematic phases due to their flexible back- bone. Mesophase identification has been accomplished by DSC measurement and polarized optical microscopic observation. Figure 7 shows a representative DSC trace of copolymer PECHOC2-B. It exhibited two endothermic peaks at 76.5 8C and 145 8C in the first heating scan. Pola- rized optical microscopy (shown in Figure 8) shows a nematic phase transition at 110 8C. Interestingly, unusual high-strength disclination (s) of 3/2 (six dark brushes, Figure 8(a)) was observed, which have been observed in a few systems of main-chain liquid crystalline polymers with rigid backbones but has never been reported for any side- chain liquid crystalline polymers with flexible back- bones.[45–47] All thermal properties of the PECHOCn-B series copolymers are listed in Table 3. These data have been extracted from the second heating cycles of the DSC curves from Figure 7 and 9. The DSC curve for PECHOC3- B shows two endothermic peaks (see Figure 9). When PECHOC3-B is cooled from the isotropic phase, a well- defined Schlieren texture (shown in Figure 10) appears, which indicate a nematic phase. The DSC curves for PECHOCn-B (n¼ 4–6) are similar to PECHOC3-B, when PECHOCn-B (n¼ 4–6) is cooled from the isotropic phase, a well-defined nematic Schlieren texture develops, which is assigned as a nematic phase shown in Figure 11 to 13. Figure 14 shows the dependence of the transition tem- peratures on the length of the flexible alkyl spacer for the Figure 4. 1HNMR spectra of monomer: (a) HOC3-B, (b) PECH and copolymer (c) PECHOC3-B. Figure 5. DSC thermogram of monomer HOC4-B at rate of 10 8C �min�1, (a) heating, (b) cooling. Figure 6. Polarized optical micrograph of HOC4-B Schlieren texture taken at 110 8C. Table 3. Properties of synthesized PECHOCn-B copolymers. Compounds Substitution degreea) Tm b) Tn-i c) % 8C 8C PECHOC0-B 91 87 110 PECHOC2-B 89 76 145 PECHOC3-B 85 71 124 PECHOC4-B 78 86 114 PECHOC5-B 70 62 116 PECHOC6-B 65 66 106 PECHOC7-B 25 54 – PECHOC8-B 15 56 – a) Phase transfer catalyst TBAH¼ 11.8 mmol; reaction tempera- ture: 60 8C. b) Melting temperature. c) Transition from nematic phase to isotropisation temperature. Synthesis and Characterisation of Side-Chain Liquid Crystalline Poly[1-({[(4-cyano-40-biphenyl)oxy]alkyl}oxy)-2,3-epoxypropane] 747 Macromol. Chem. Phys. 2004, 205, 743–751 www.mcp-journal.de � 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim copolymers. The melting temperature and the clearing temperature both exhibit a small alternation that attenuates slowly on increasing the spacer length. The alternation in the Tm and Tn-i is unusual and can be explained in the terms of the different substitution degree of PECH. The seventh and eighth members do not exhibit liquid crystalline beha- vior because of their lower substitution degree. A small odd-even effect in the clearing temperature can be seenwith the odd members exhibiting the higher values. This may be rationalized by considering the average shape of the side chains as the spacer length and parity is varied and its effect on the relative orientation of the mesogenic groups (shown in Figure 15). The spacer length also affects the conformational entropy change, for an even-membered spacer, themesogenic unit is orthogonalwith respect to the backbonewhereas for an odd- membered spacer the mesogenic group forms angle to the backbone. Clearly this assumes that the backbone lies in a plane orthogonal to the director. Figure 15 shows the effect of introducing a single gauche defect into a flexible spacer. It is clear that for the even spacer (Figure 15(a)) there exist more conformations for which the mesogenic units are co- parallel, and thus the interactions between them are maxi- mized. Also, these more elongated conformers are more favoured in a liquid crystalline environment, and hence at the clearing temperature there is a greater conformational entropy change for the even-member spacer than there is for the odd-member spacer. Figure 7. DSC thermograms of PECHOC2-B: second heating (upper curve) and cooling (lower curve) scan. Figure 8. Schlieren textures with disclination strengths of 3/2 and 2 of PECHOC2-B taken at 110 8C (cooling from isotropic phase after annealing 1 h). Figure 9. NormalizedDSC thermograms of PECHOCn-B series second heating scan. Figure 10. Polarized optical micrograph of PECHOC3-B Schlieren texture of nematic phase taken at 100 8C (cooling from isotropic phase). 748 X. Han, R. A. Shanks, D. Pavel Macromol. Chem. Phys. 2004, 205, 743–751 www.mcp-journal.de � 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim To establish the effects of backbone flexibility on the transitional properties of SCLCPs, Figure 14 and 16 com- pare the glass transition temperatures and clearing tem- peratures, respectively, of the polyacrylate-based PAOCn-B series, and the polymethacrylate-based PMAOCn-B series.[17,48–54] Figure 14 and 16 also show the transition temperatures for the analogous polymers containing 4-cyanobiphenyl as the mesogenic unit, i.e., the poly[n- (4-cyanobiphenyl-40-yloxy)alkyl acrylate]s (PAOCn-A) and the poly[n-(4-cyanobiphenyl-40-yloxy)alkyl methacry- late]s (PMAOCn-B) (see Figure 1(a) and (b)). For all three series of polymers, the glass transition temperature tends to decrease as the length of the flexible alkyl spacer increases (see Figure 14). This decreasing trend implies a plasticisation of the polymer backbone by the side groups.On the basis of backbone flexibility alone, it would be expected that the series based on themore flexible PECH backbone would yield side-group liquid crystal polymers having lower glass transition temperatures than the analogous polyacrylates and polymethacrylate-based materials. This expectation is realized. But the glass tran- sition temperatures of the corresponding polyacrylate and polymethacrylate-based materials are remarkably similar, even polymethacrylate–based materials is more rigid than polyacrylate’s. Figure 15 shows the dependence of the clearing tempe- rature on the length of the alkyl spacer, n, for each series. The PAOCn-B series exhibits higher clearing temperatures than the PMAOCn-B series. This behavior is consistent with the view that increasing backbone flexibility enhances the clearing temperature. In comparison, the clearing tem- peratures for the PECHOCn-B series do not exhibit the ex- pected trend. Specifically, the even members of the PECHOCn-B series show lower clearing temperatures than the corresponding member of the PMAOCn-B and PAOCn- B series. In an attempt to understand this behavior as well as the trends observed in the glass transition temperatures, the smectic phase structures of two of the odd members of the PAOCn-B series, see Figure 14, it is clear that the higher glass transition temperatures are observed for polymers which exhibit smectic phases. Specifically, the two PAOCn- B and PMAOCn-B series, which exhibit SA phases, show Figure 11. Polarized optical micrograph of PECHOC4-B Schlieren texture taken at 90 8C (cooling from isotropic phase). Figure 12. Polarized optical micrograph of PECHOC5-B Schlieren texture taken at 90 8C (cooling from isotropic phase). Figure 13. Polarized optical micrograph of PECHOC6-B Schlieren texture taken at 90 8C (cooling from isotropic phase). Figure 14. Dependence of the glass transition for the PAACn-A (&), PMAACn-B (^) andmelting temperature for PECHOCn-B (~), on the number of methylene groups, n, in the spacer. Synthesis and Characterisation of Side-Chain Liquid Crystalline Poly[1-({[(4-cyano-40-biphenyl)oxy]alkyl}oxy)-2,3-epoxypropane] 749 Macromol. Chem. Phys. 2004, 205, 743–751 www.mcp-journal.de � 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim higher glass transition temperatures than the analogous PECHOCn-B series, which form nematic phases. A simi- lar relationship between phase structure and the glass transi- tion temperature has been noted for polystyrene-based materials.[38–41] Now turn the attention to the relationship between polymer structure and the clearing temperature. Given that the PMAOCn-B and PECHOCn-B series exhibit different modification of the smectic A and nematic phases, respec- tively, and that the spacer and mesogenic groups in each are identical, the differences in phase behavior and in the transition temperatures must be related to the flexibility of the backbone. The PECHOCn-B series has a tendency to exhibit less ordered nematic phases than the PMAOCn-B series. Thus, flexible backbones tend to exhibit lower mel- ting temperatures than more rigid backbones. It is reason- able to assume, therefore, that the clearing temperatures of the PECHOCn-B seriesmay also be entropically driven and this would explain why these are lower than expected. In comparison, for SA phases, the driving force is the elec- trostatic interaction between the polar and polarizable 4-cyanobiphenyl groups and is determined largely by the ability of the mesogenic groups to interact. Thus, for 4-cyanobiphenyl containing polymers, PAOCn-B and PMAOCn-B series, the clearing temperature increases with backbone flexibility, which facilitates the mesogen-meso- gen interactions. Therefore, the relationship between the clearing temperature and backbone flexibility depends, at least in part, on the nature of the liquid-crystalline phase. Conclusion Polyepichlorohydrin-based SCLCPs have been synthesized by nucleophilic substitution. The structure of the synthe- sized copolymers was confirmed by IR and 1H NMR spectroscopy. All of the copolymers were obtained by nucleophilic displacement of the halogen of polyepichlor- ohydrin according to a previously developed synthetic approach. All the purified chemical modification products gave satisfactory spectroscopic data corresponding to their expected molecular structures. Thermal properties of eight members of a polyepichlor- ohydine-based side-chain liquid crystal copolymer series incorporating cyanobiphenyl as the mesogenic group have been reported, which provide nematic texture (except seventh and eighth member) is proved. LC formation are shown to be dependent on spacer length. A more pronounced odd-even effect in the clearing temperatures is observed on increasing the spacer length in which the odd members display higher values, which were also dependent on the substitution degree of PECH. Flexi- ble PECH chain assists nematic LC formation compared with other more rigid backbone polymers where smectic phase is often encountered with the same mesogen. A comparison of the thermal properties of the cyanobi- phenyl based series reported here. Polyacrylate (PA) and poly(methacrylate)-based (PMA) SCLCPs containing 4-cyanobiphenyl as the mesogenic group are consistent with the general rule that increasing backbone flexibility for a given mesogenic group and spacer length enhance the clearing temperature. This was not found from the PECH- based series, which show the lower clearing temperature than the PMA and PA series, even though they have more flexible backbone than PA and PMA series. So the clearing temperature is not solely determined by the flexibility of the backbone. An unusual high-strength disclination (s) of 3/2 (six dark brushes) were observed, which have been observed in a few systems of main-chain liquid crystalline polymers with rigid backbones but have never been reported for any side- chain liquid crystalline polymers with flexible backbones. Acknowledgement: We are pleased to acknowledge support from Australian Government (IPRS scholarship), RMIT University and Lanzhou Jiaotong University. Figure 15. Schematic representation in two dimensions of the effect of introducing a single gauche effect into the flexible spacer of a SCLCP. Figure 16. Dependence of the clearing transition temperatures for the PECHCn-B (&), PAACn-B (~) and PMAACn-B (&), on the number of methylene groups, n, in the spacer. 750 X. Han, R. A. Shanks, D. Pavel Macromol. Chem. Phys. 2004, 205, 743–751 www.mcp-journal.de � 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim [1] H. Finkelmann, M. Happ, M. Portugall, H. Ringsdorf, Makromol. Chem. 1978, 179, 2541. [2] T. Ikeda, Kino Zairyo 1993, 13, 19; Chem. Abstr. 1993, 112650. [3] T. Ikeda, T. Sasaki, S. Osamu, Synth. Met. 1996, 81, 289. [4] S. Hvilsted, F. Andruzzi, C. Kulinna, H. W. Siesler, P. S. Ramanujam, Macromolecules 1995, 28, 2172. [5] X. Meng, A. Natansohn, C. Barrett, P. Rochon, Macro- molecules 1996, 29, 946. [6] M. Trollsas, F. Sahlen, U. W. Gedde, A. Hult, D. Hermann, P. Rudquist, L. Komitov, S. T. Lagerwall, B. Stebler, J. Lindstrom, O. Rydlund, Macromolecules 1996, 29, 2590. [7] P. Wang, M. Hai, Z. Liang, J. Zhang, Opt. Commun. 2002, 203, 159. [8] Y. L. Wu, A. Kanazawa, T. Shiono, T. Ikeda, Q. J. Zhang, Polymer 1999, 40, 4787. [9] H. K. Lee, K. Doi, A. Kanazawa, T. Shiono, T. Ikeda, T. Fujisawa, M. Aizawa, B. Lee, Polymer 2000, 41, 1757. [10] L.Andreozzi,M. Faetti,M.Giordano,M.Hyala, G.Galli,M. Laus,Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A 2002, 372, 229. [11] V. Percec, C. Pugh, ‘‘Side chain liquid crystal polymers’’, Blackie and Sons, Glasgow 1989, Chap. 3. [12] V. Percec, D. Tomazos, in: ‘‘Comprehensive Polymer Science’’, 1st Supplement, Pergamon Press, Oxford 1992, Chap. 14. [13] C. T. Imrie, D. Ionescu, G. R. Luckhurst, Macromolecules 1997, 30, 4597. [14] H. Ringsdorf, H. W. Schmidt, G. Strobl, R. Zentel, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 1983, 24, 306. [15] C. T. Imrie, F. E.Karasz, G. S.Attard,Macromolecules 1993, 26, 3803. [16] A. A. Craig, I. Wincheste, P. C. Madden, P. Larcey, I. W. Hamley, C. T. Imrie, Polymer 1998, 39, 1197. [17] S. G. Kostromin, V. V. Sinitsyn, R. V. Tal’rose, V. P. Shibaev, Vysokomol. Soedin., Ser. A 1984, 26, 335;Chem. Abstr. 1984, 157235. [18] C. T. Imrie, L. Taylor, Liq. Cryst. 1989, 6, 1. [19] S. G. Kostromin, V. P. Shibaev,Makromol. Chem. 1990, 191, 2521. [20] T. Ikeda, S. Kurihara, D. B. Karanjit, S. Tazuke, Macro- molecules 1990, 23, 3938. [21] V. Percec, M. Lee, Macromolecules 1991, 24, 2780. [22] V. Percec, M. Lee, Macromolecules 1991, 24, 1017. [23] A. A. Craig, C. T. Immrie,Macromolecules 1991, 28, 3616. [24] S. Kurihara, T. Ikeda, S. Tazuke,Macromolecules 1991, 24, 627. [25] Z. Komiya, C. Pugh, R. R. Schrock, Macromolecules 1992, 25, 3609. [26] S. Kurihara, T. Ikeda, S. Tazuke,Macromolecules 1993, 26, 1590. [27] H. Fischer, S. Poser, M. Rnold, W. Frank, Macromolecules 1994, 27, 7133. [28] P. Iannelli, S. Pragliola, A. Roviello, A. Sirigu, Macro- molecules 1997, 30, 4247. [29] A. M. Kasko, S. R. Grunwald, C. Pugh, Polym. Prepr. (Am Chem. Soc., Div. Polym. Chem.) 2001, 42, 160. [30] X. H. He, H. L. Zhang, D.Y. Yan, X. Y. Wang, J. Polym. Sci., Part A: Polym. Chem. 2003, 41, 2854. [31] X. J. Hao, J. Heuts, C. Barner-Kowollik, T. Davis, J. Polym. Sci., Part A: Polym. Chem. 2003, 41, 2949. [32] J.W.Y. Lam,B. Z. Tang, J. Polym. Sci., Part A:Polym.Chem. 2003, 41, 2607. [33] N. Lacoudre, A. L. Borgne, N. Spassky, J. P. Vairon, Mol. Cryst. Liq. Cryst. 1988, 155, 113. [34] Y. Kosaka, T. Uryu,Macromolecules 1995, 28, 870. [35] A. A. Craig, I. Winchester, C. P. Madden, P. Larcey, W. I. Hamley, T. C. Imrie, Polymer 1998, 39, 1197. [36] V. Percec, D. Tomazos, Polymer 1990, 31, 1658. [37] A. Mirceva, M. Zigon, Polym. Bull. 1998, 41, 447. [38] T. C. Imrie, E. F. Karasz, Macromolecules 1992, 25, 1728. [39] T. C. Imrie, E. F. Karasz, Macromolecules 1993, 26, 3803. [40] T. C. Imrie, E. F. Karasz, Macromolecules 1993, 26, 545. [41] T. C. Imrie,Macromolecules 1996, 29, 1031. [42] C. Pugh, V. Percec, Polym. Bull. 1986, 16, 521. [43] S. Ujiie, K. Iimura, Polym. J. 1992, 24, 427. [44] X. E. Han, R. A. Shanks, D. Pavel, Polymer Processing Society, 19th Annual Meeting Melbourne, Australia, 2003, 12, 320. [45] W. Song, S. Chen, R. Y. Qian, Makromol. Chem. Rapid Commun. 1993, 14, 605. [46] Q. F. Zhou, X. H. Wan, F. Zhang, D. Zhang, Z. Wu, X. D. Feng, Liq. Cryst. 1993, 13, 851. [47] H. Witteler, G. Lieser, G. Wegner, M. Schulze, Makromol. Chem. Rapid Commun. 1993, 14, 471. [48] V. P. Shibaev, S. G. Kostromin, N. A. Plate, Eur. Polym. J. 1982, 18, 651. [49] S. G. Kostromin, R. V. Talroze, V. P. Shibaev, N. A. Plate, Makromol. Chem. Rapid Commun. 1982, 3, 803. [50] S. Kurihara, T. Ikeda, S. Tazuke,Macromolecules 1991, 24, 627. [51] F. J. Bormuth, A.M. Biradar, U. Quotschalla, W. Haase, Liq. Cryst. 1989, 5, 1549. [52] S. Kurihara, T. Ikeda, S. Tazuke,Macromolecules 1993, 26, 1590. [53] T. I. Gubina, S. Kise, S. G. Kostromin, R. V. Talroze, V. P. Shibaev, N. A. Plate, Liq. Cryst. 1989, 4, 197. [54] S. G. Kostromin, V. P. Shibaev,Makromol. Chem. 1990, 191, 2521. Synthesis and Characterisation of Side-Chain Liquid Crystalline Poly[1-({[(4-cyano-40-biphenyl)oxy]alkyl}oxy)-2,3-epoxypropane] 751 Macromol. Chem. Phys. 2004, 205, 743–751 www.mcp-journal.de � 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim