Solution properties of two liquid crystalline side-chain polymers of different architecture have been investigated by static and dynamic light scattering. Dilute solutions of these polymers showed common flexible chain behavior, and no indications for a significant chain rigidity were observed. In semidilute solution the concentration dependence of the osmotic modulus revealed stronger repulsion than common linear macromolecules. Furthermore, a chain-length dependence was observed. Both effects can be explained by the thickness of the polymer chain. At high concentrations an excess low-angle scattering and a slow mode of motion were detected, indicating formation of large clusters. The first appearance of these clusters was found at the same concentration for samples of different molar mass. This leads to the suggestion that attractive interactions between mesogenic groups are responsible for cluster formation. Further information on the structure of the clusters was obtained by studying fractal dimension and depolarized scattered light.
Measurements of stress and birefringence of crosslinked liquid-crystalline side chain polymers are reported. The results are compared with those obtained for conventional elastomers. It is found that the thermoelastic behaviour in the nematic state completely differs from that observed for common polymer networks due to the anisotropic ordering of the mesogenic side chains. The retractive force in the nematic state is found to be independent of path, indicating that the nematic phase is a homogeneous phase. Photoelastic investigations prove the proportionality of stress and birefringence above the clearing temperature T, which is similar to common elastomers. The stress-optical coefficient, however, strongly depends on temperature in the pretransformation region. X-ray measurements show a uniform orientation of the mesogenic side groups in the nematic state. The diffraction patterns observed contain many more reflexes than observed for common nematics.
A B S T R A C TIf low molar mass mesogenic molecules, which are able to form a liquid crystalline phase, are linked as side groups to a polymer main chain, a new class of polymeric substances with liquid crystalline behaviour is obtained. Nematic, smectic and cholesteric elastomers have been synthesized. The new material is marked by a new combination of liquid crystalline and elastomer specific properties. Above the glass temperature,T ,the substances are rubber-elastic. Starting from the elastomer in the optical isotropic state, a first order phase transformation into the liquid crystalline state is obtained by decreasing the temperature. By further cooling the liquid crystalline elastomer is converted into an anisotropic liquid crystalline glass.
9The thermoelastic and optoelastic properties of the networks have been investigated by uniaxial deformation (compression, elongation) and birefringence measurements. Above the transformation point nematic-isotropic, Tn-i, the thermoelastic behaviour is the same as for usual elastomers. However, when the transformation temperature is reached, the nominal stress decreases rapidly. If one passes to temperatures below the transformation temperature by maintaining the deformation of the network, the liquid crystalline order is built up in a sample having a preferential direction. This is the reason for the unusual stresstemperature behaviour observed.
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