Phase transition behaviors of dimer and trimer mainchain compounds such as α, ω-bis (4-cyanobipheny1-4′-yloxy) -alkanes (CBA-n, n=9, 10) and 4, 4′-bis [ω- (4-cyanobiphenyl-4′-yloxy) alkoxy] biphenyls (CBA-Tn, n=9, 10) have been extensively studied by using spectroscopic (²H NMR) as well as thermodynamic (PVT) techniques. These compounds exhibit an enantiotropic nematic liquid crystalline (LC) state over wide temperature range above the crystalline solid phase. Since both mesogenic units and the intervening spacer segment tend to align more or less in one direction in the LC state, mesogenic core axes remain inevitably inclined with respect to the nematic domain axis; such a requirement does not exist in low-molar-mass (monomer) LCs. While the orientational order of the molecular axis varies as a function of temperature, the nematic conformation of the spacer remains quite stable over the entire range of LC state. The analysis of the PVT data indicates that about 50-60% of the transition entropy observed under atmospheric pressure arises from the variation in the conformational distribution. It has been pointed out that the stereochemical role and thermodynamic significance of the spacer elucidated in this study should be applicable to polymeric mainchain LC systems as well.

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Morphology of the two types of main-chain smectic liquid crystal polyesters, BB-n and PB-n, was studied by small angle X-ray scattering (SAXS). The SAXS for the crystalline BB-6 specimens prepared by cooling the smectic A melt shows well-defined reflection maxima which are attributable to the stacked lamellar structure. The lamellar spacings are distributed around 250Å so that an appreciable number of chain foldings are included in a chain. The lamellar spacing is increased by annealing the crystal. In contrast, it is not essentially altered by annealing the smectic A phase. The increment of the lamellar spacing was caused by a decrease in the crystallization temperature. This trend is contrary to that observed in conventional polymers which crystallize from the isotropic melt. The results show that the chain foldings are at a thermodynamic equilibrium by an entropy effect in the smectic A phase. The well-defined reflection maxima were observed for the smectic H phase of PB-14 polyester. The lamellar size increased from 300250Å to 500250Å with an increase in the liquid crystallization temperature of 190°C to 220°C. The relationship between the lamellar thickness and isotropization temperature is well described by the Thomson-Gibbs equation. When the sample was annealed at a smectic H temperature of 215°C, the isotropization temperature and enthalpy of the smectic H phase increased. The overall results thus indicate that the smectic H liquid crystallization at a certain temperature takes place imperfectly in a finite period due to the chain folding and that the succeeding annealing causes the alternation of the chain conformation from a folded form to an extended one as observed in the crystallization of conventional polymers.

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A liquid crystalline copolyester consisting of 60 mol% p-hydroxybenzoic acid/40 mol% ethylene terephthalate units was aligned in a magnetic field (6T), and the structure and the tensile/thermal properties of these oriented films were studied in comparison to these properties of mechanically stretched films. The elastic modulus of the magnetically oriented films was as high as that of the mechanically stretched films, but the ultimate tensile strength was slightly lower. It was found that the structure of the aligned films viewed in a molecular level as well as a micron level depended on the orientation method used, which might be responsible for the difference in physical properties. Magnetic orientation of crystalline polymers including poly (ethylene-2, 6-naphthalate) (PEN) and isotactic polystyrene was reported. The orientation was observed during the induction period of isothermal crystallization from melts, prior to the formation of crystals. The PEN sample crystallized inside the magnet (6T) exhibited the orientation with the a-axis normal to and the c-axis parallel to the magnetic field in consistent with the diamagnetic anisotropy of the naphthalene ring. In situ FT-IR study demonstrated that the trans conformers in the amorphous phase increase during the induction period, prior to the crystallization.

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The phase transition behavior and the dielectric relaxation behavior of side-chain liquid-crystalline polyacrylates having an alkylene-spacer (AS), a siloxane-spacer (SS), an oligo (ethylene oxide) -spacer (EOS), and a segmented spacer (SegS) were investigated in order to reveal the effects of a spacer part on such behaviors. The increase of the flexibility of a spacer-chain by the introduction of SS or EOS enhanced the mobility of a mesogenic group. But, in these cases, the introduction o a relatively large mesogenic group was necessary to exhibit a liquid-crystalline phase. In addition, the introduction of as small a mesogenic group as possible was very important for the increase of the mobility of a mesogenic group. Consequently, I proposed the segmented spacer, which consisted of the binary components of a flexible oligo- (ethylene oxide) -segment and an alkylene-segment. The SegS series showed a very low glass transition temperature and had the high mobility of a mesogenic group. For SegS, the oligo (ethylene oxide) -segment plays the role of decoupling the motions of a polymer-backbone and a mesogenic group, and also contributes to the decrease of the interactions between polymer-backbones and/or a polymer-backbone and an anisotropically ordered layer of mesogenic groups. The alkylene-segment plays the role of the control of the interaction between mesogenic groups. Furthermore, the fully aligned sample of SegS-3 on the macroscopic level was obtained by applying an external electric field.

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We have synthesized novel side-chain liquid crystalline (LC) conducting polymers by introducing LC groups into acetylene monomers and polymerizing them with Ziegler-Natta [Fe (acac) ₃-AlEt₃], metathesis [MoCl₅-Ph₄Sn], and rhodium-based { [Rh (NBD) Cl] ₂-NEt₃} catalysts. All polymers prepared exhibited solubility in organic solvents and smectic liquid crystallinity characterized by fan-shaped texture in polarizing optical microscopy. Phase transitions and the corresponding enthalpy changes were evaluated by means of differential scanning calorimetry (DSC). High order structures of the LC polyacetylene derivatives were investigated by means of X-ray diffraction (XRD) analysis. XRD measurements elucidated that all of the polymers showed layered structures in the LC states to give smectic A phases, which is in agreement with the results from the polarizing optical microscopy. It is found that the LC side chains are alternatively located on both sides of the polyene chain, giving rise to a stereoregular sequence such as a head-head and tail-tail linkage. Macroscopic alignments of the polymers were performed in the LC phase by shear-stress or magnetic force field of 0.7-1.0 Tesla, which resulted in an enhancement by two orders in electrical conductivity of iodine-doped cast films. Magnetically forced alignments and orientational behavior of the polymers as well as the monomers were investigated through fused-state ¹³C NMR measurements with proton dipolar decoupling. Analysis of chemical shift tensors was carried out to evaluate the order parameter and shielding anisotropy in the LC phase. As a result, it is demonstrated that the LC conjugated polymers are uniaxially aligned as a result of the magnetically forced alignment of the LC side chain, forming a mono domain structure.

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We describe here the synthesis and photoreaction of photo-crosslinkable polymer liquid crystals comprising 4- (methoxycinnamoyloxyalkyloxy) biphenyl side group. After the linearly polarized UV irradiation, the negative or positive dichroism in absorption spectrum was observed, depending on the reaction temperature. The nematic liquid crystals could be aligned on the photoreacted polymer films. The alignment direction was controlled by changing the exposure doses.

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We synthesized various kinds of side chain-type polyethers. The side chain-type polyether exhibited smectic phase when the alkoxy side chain length was below 12. A smectic phase was also induced for the mixture of non-mesomorphic side chain-type polyethers with alkali metal salts. The mesomorphic temperature range for the mixed system became wider with increasing amounts of alkali metal salts. These mixtures had ionic conductivity. The complex impedance measurements were carried out in order to clarify the relationship between ionic conductivity and liquid crystalline properties for the polyether-LiClO₄ mixtures. The conductivity values of mesomorphic and non-mesomorphic polyether with lithium perchlorate were 5.38×10^-6 Scm^-1 and 4.57×10^-7 Scm^-1 (0.67=LiClO₄/polymer repeat unit, 100°C), respectively.

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Anisotropic polymer/liquid crystal composite films containing azobenzene molecules were prepared by thermal polymerization of liquid crystalline mixtures at a nematic phase in a homogeneous glass cell. The polymer network was transparent because of its macroscopic uniaxial alignment. Upon photoirradiation to cause trans-cis photoisomerization of azobenzene molecules, the polymer network became translucent even at room temperature. The system does not require the use of polarizers and electrodes to fabricate optical devices. The light scattering is ascribed to a biphase morphology in the system produced transiently by means of the photochemical phase transition. Flexible polymer chains are responsible for the photochemically light scattering of the composite films.

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The liquid crystallinity of concentrated solutions of polymacromonomer (SS-33) samples consisting only of polystyrene with a fixed side chain length of 33 styrene residues was examined using various solvents for polystyrene. Toluene, carbon tetrachloride, and ethylene dichloride solutions of the samples lost the fluidity to form physical gels before forming liquid crystal phases, when the polymer concentration was increased. On the other hand, concentrated dichloromethane (DCM) and chloroform solutions of SS-33 exhibited birefringence to form a nematic phase. The phase boundary concentration c_I, where SS-33 solutions start showing birefringence, was determined for DCM solutions as a function of the polymer molecular weight. The results were rather close to the prediction from the scaled particle theory with the wormlike-chain parameters estimated from dilute solutions studies. However, the experimental molecular weight dependence of c_I was appreciably stronger than theoretically predicted, and some problems of the scaled particle theory, originally proposed for linear stiff-polymer solutions, were pointed out.

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New semi-rigid polyesters were synthesized by high temperature solution polycondensation from a diacid chloride of terphenyl analogue, (2, 5-diphenyl-1, 3, 4-thiadiazole), which has central 1, 3, 4-thiadiazole and benzene rings at both the sides, and aliphatic diols. The polymers obtained were insoluble in most of the organic solvents expect dichloroacetic acid and trifluoroacetic acid. DSC measurements and polarizing microscope observations of textures indicated that polyesters having longer aliphatic chains (m=9, 10, 12) form thermotropic smectic phases, but those with shorter aliphatic chains (m=6, 8) decompose without showing clear liquid crystalline phases.

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