Rheological and structural features of liquid crystal polyalkylene fumaroyl- bis-4-oxybenzoates

Abstract

The rheological, thermodynamic, and structural properties of liquid crystal polyesters, i.e. polyhexa- and polydecamethylene fumaroyl- bis-4-oxybenzoates and of the statistical copolymer based on them are studied. All these polymers form a smectic phase in the liquid crystal region. The transition from homo- to copolymer results in widening of the region over which the liquid crystal phase exists. A feature of the copolyester is the high sensitivity of its structure to the thermal prehistory in the melting region. In this case protracted annealing results in a fundamental rearrangement of the copolymer structure, beginning from the melt, and indicated by a sharp increase of viscosity with time. When the shear stresses are large a high degree of molecular orientation along the flow direction is realized, the smectic layers being located perpendicular to this direction. In the melting region the existence of a metastable network with crystalline lattice sites is superimposed on the special features of the flow of the homo- and copolyesters. The structure of the elementary cell of the crystallites depends on the composition and thermal prehistory.