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.
Abstract:The optical anisotropy Aa (a = polarizability) of uniaxial deformed swollen and unswollen PMMA networks depends on the temperature. This is not in agreement with the Kuhn-Griin-theory. The temperature dependence and the negative values even above the glass transition temperature 7[2 can be explained by the existence of associations which cause a hindrance of the ester side group mobility. The swelling of the network in the optical isotropic solvent carbon tetrachloride does not degrade the associations and therefore not change the network structure; only Tg decreases. The situation is more complicated if optical anisotropic solvents are used. Polar aliphatic and aromatic solvents degrade the associations to some extend and the birefringence is shifted to more positive values. An additional change is caused by specific polymer solvent interactions. Aromatic solvents form complexes with the ester side group and the aliphatic solvent chloroform completely degrades the associations, which can be explained by the formation of hydrogen bonds. Sign and magnitude of the optical anisotropy allow statements on the orientation of the solvent molecules with respect to the polymer chain or the ester side group.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.