Molecular Mass and Structure Dependence of Liquid Crystalline Properties for a Homologous Series of Polyesters

Abstract

Mesomorphic properties of higher homologues of flexible main chain thermotropic polyesters based on regularly alternating p-dioxy,2,2′dimethylazoxybenzene mesogen and (α,αω)-alkanedicarboxylic acid were investigated. Attention was given to changes from cybotactic nematic to smectic C (N_c—S_c) mesophases. On the basis of SAX data, rheology and miscibility diagrams with low M compounds displaying both a S_c and N_c mesophase it was shown that the polyester with n=18 and M > 3,000 displays a S_c monotropic mesophase. The data suggest that while polyesters of odd spacer parity in the nematic quiescent state do not display any tendency toward formation of layered order, polyesters with n even exhibit a pronounced tendency toward the formation of layered order, This tendency increasing with n and M is favored by a decrease of temperature. It may be argued that the observed passage N_c—S_c is continuous. The formation of layered (N_c) order was also observed for large n and M for a spacer of odd parity but only as a result of fiber drawing.