Thermotropic Polyesters with Flexible Spacers Bearing Ether Bonds in Asymmetric Position

Abstract

The synthesis of several polyesters from p, p ‘-bibenzoic acid and diols bearing ether bonds in asymmetric positions is described. The polyesters develop smectic mesophases, the type of which depends on the chemical structure of the spacer. The ether groups and the asymmetry of the spacers stabilize the liquid crystalline order in these polymers. Glass transition and isotropization temperatures, enthalpies, and entropies of the thermotropic polyesters are reported. Comparison of the melting entropies with the conformational entropies of the chains suggests a great disorder in the mesophases of thermotropic polyesters. For some polyesters, the stretched polymer chains do not follow the direction of the fiber axis, an unusual phenomenon that has already been described for some polybibenzoates with aliphatic separators. The influence of the strain rate on the anomalous flow is discussed.