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The possibility has been indicated that polymers with helical chirality, such as poly-γ-benzyl-L-glutamate (PBLG) and poly-L-lactic acid (PLLA), exhibit a large shear piezoelectric constant. To attempt the realization of a PBLG membrane with a large piezoelectric constant, we fabricated the PBLG membrane oriented by magnetic field force. Concretely, the PBLG membranes were casted from 1,2-dichloroethane solution with various PBLG concentrations under the magnetic field generation equipment incorporating a superconducting magnet. First, the orientation of the chain molecules of the PBLG membranes obtained was observed macroscopically by means of a polarizing microscope (POM). The orientation of the chain molecules of the PBLG membranes was recognized for the case of casting from the PBLG 1,2-dichloroethane solution in the liquid crystal state. Also, from X-ray photograph measurements, it was found that the orientation direction of the chain molecules of PBLG was perpendicular to the magnetic field direction. We then measured the shear piezoelectric constant d 14 of the oriented PBLG membranes. With increasing the strength of the applied magnetic field in the casting process for the film preparation, d 14 * of the PBLG membranes obtained increases. Finally, a large piezoelectric constant of 26 pC/N was found in the PBLG membrane. It is assumed that d 14 * is not saturated even at the magnetic field of 10 T.

The effect of solvents on the structure and preperties of cast films of poly(r-benzyl glutamate) (PBLG) were studied. From X-ray diffraction measurements, it was found that films cast from dichloroethane, chloroform, and dichloromethane (called film A) had a well-ordered structure consisting of helices packed on a regular hexagonal lattice, while films cast from benzene and tetrahydrofuran (called film B) showed less crystallinity than film A. As for viscoelastic properties, film A showed peaks of tan iJ at 38 and 105°C (110 Hz). In the case of film B, the lower-temperature peak was shifted to a higher temperature and the peak was broadened. Film B further exhibited a remarkable decrease of modulus at about 135°C, which was accompanied with a small peak of tan iJ at this temperature. After being annealed at 140°C, film B showed a remarkable increase in its tan iJ peak at 105°C and simultaneously the lowertemperature peak shifted to 40°C and the peak at 135°C vanished. To elucidate these changes, differential thermal analysis (DT A) was performed. The DT A thermogram on film B showed an endothermic peak at 135°C, which was not observed after the film was annealed at 140°C. From the fact that the aggregates of superhelices of PBLG, which were precipitated from dimethylformamide solution by adding propionic acid, also showed an endothermic peak at 135°C, it is argued that the superhelical structure exists in the solid state of film B and stacks of benzene ring in the side chain are responsible for the characteristic behaviors of film B.

It has been reported that there is a special side chain-side chain interaction between the right-handed and left-handed a-helices in the racemic mixture of poly-(r-benzyl glutamate). In this paper physical properties of mixtures of poly(r-benzyl-Lglutamate) and poly(r-benzyl-n-glutamate) are studied. From X-ray diffraction measurements, the reflection characteristic of the regular arrangement of the benzyl group at the end of the side chain was shown to disappear on heating at 97°C and to appear on cooling at 73°C. This reversible change was also observed in viscoelastic, thermal and dilatometric measurements and was ascribed to the breakdown and formation of stacks of benzene rings. In the case of samples cast from benzene solution, it was found that the formation of stacks is hampered by the preferable superhelix formation. KEY WORDS Racemic Mixture I Poly(r-benzyl glutamate) I Stack I First-Order Transition I Physical Properties I

The cholesteric liquid crystals formed by poly(y-benzyl L-glutamate) (PBLG) in various solvents exhibit a cholesteric sense inversion when the temperature or the solvent composition is changed. The sense inversion in 1,2,3-trichloropropane and in m-cresol occurs from rightto left-handed via an untwisted nematic state with increasing temperature. The helical twisting power (reciprocal of the cholesteric half-pitch) in mixtures of these two solvents shows a quadratic dependence on the solvent composition, accompanied by a two-fold sense inversion (right 4 left 4 right) at low temperatures. The measurements of the twisting power are also reported for PBLG in a series of alkylchlorides in order to establish the role of solvent. In solvents with low dielectric constants PBLG forms the right-handed cholesteric structure while it changes to the left-handed one when the dielectric constant is increased beyond a critical value of ca. 9. The increase in temperature enhances the left-handed twisting power in all solvents studied here regardless of the cholesteric sense at room temperature. These observations clearly separate the effects of solvent and temperature on the cholesteric structure and are discussed in comparison with theories.

ABSTRACT:Thermally induced inversion of the cholesteric sense has been found in lyotropic polypeptide liquid crystals. The cholesteric sense of poly(y-benzyl L-glutamate) liquid crystal in mcresol (17 vol%) inverts from right to left at 60°C, and the reciprocal of the cholesteric pitch changes linearly with temperature. The compensated liquid crystalline solution at 60°C shows no helical twist. Similar phenomena are found for poly(y-benzyl L-glutamate) in benzyl alcohol and for poly(y-propyl L-glutamate) in m-cresol. The solvent effect on the helical twisting power is discussed in the light of the fact that the side-chain ester groups of poly(y-benzyl L-glutamate) form hydrogen bonds with the hydroxyl groups of m-cresol.KEY WORDSConcentrated solutions of poly(y-benzyl L-glutamate) (PBLG) and poly(y-alkyl L-glutamate)s (alkyl=methyl, ethyl and propyl) in certain organic solvents form cholesteric liquid crystals.1.2 The cholesteric structure in such solutions is characterized by the microscopically visible striation patterns when viewed along a direction normal to the axis of torsion. The distance between striations corresponds to one-half the pitch of the helical structure. It is known that the cholesteric pitch varies with polymer concentration, temperature and solvent. The temperature dependence of the pitch has been investigated in various solvents, such as dichloromethane, chloroform, dichloroethane, benzene, dioxane, and dimethylformamide.3.4 In all these systems, the pitch increases with temperature, in contrast to the change in ordinary thermotropic liquid crystals, for which the pitch decreases with temperature.5 The positive temperature dependence of the pitch observed for PBLG liquid crystals is usually attributed to the isotropic thermal motion of the PBLG molecule around its long molecular axis, t To whom correspondence should be addressed.which reduces the anisotropy in the intermolecular potential. 6 Robinson et a/. 2 have investigated PBLG liquid crystals in a number of solvents, and.have shown that the sense of the cholesteric twist depends on the nature of solvent. For example, the PBLG liquid crystal in dioxane forms a right-handed cholesteric structure, while in dichloromethane forms a lefthanded one. In an appropriate solvent mixture of dioxane and dichloromethane (at 0.2 volume fraction of dioxane), the solution shows no regular striation, thus indicating that the cholesteric structure is compensated. A similar compensation phenomenon has been found in a mixture of dioxane and nitrobenzene (at 0.4 volume fraction of dioxane) by DuPre et a/., 7 who also reported that the addition of trifluoroacetic acid to PBLG in dioxane (up to 10%) causes a decrease in the pitch of the cholesteric liquid crystal. There are some observations indicating the presence of intermolecular hydrogen bonds between the PBLG side chains and the solvent molecules. Electric dichroism studies show that a small amount of trifluoroacetic acid interacts with the side chain ester group either by hydrogen bonding or pro-863

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