CRYSTALLIZATION OF THERMOTROPIC LIQUID-CRYSTALLINE HBA HNA COPOLYMERS/

The crystallization behaviour of random copolymers based on p-hydroxyb enzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) is reviewed. Fi rst a summary is given of what is known about the structure and therma l transitions of the constituent homopolymers. Next the crystallizatio n behaviour of HBA/HNA copolymers is described starting with the glass transition, after which the two crystallization processes that have b een found in these copolyesters are treated. The crystallization of th e HBA/HNA copolymers will be compared to the crystallization of simila r random copolymers that are not liquid crystalline. Two models have b een proposed to describe the solid state of the HBA/HNA copolymers: th e non-periodic layer (NPL) model and the paracrystalline lattice (PCL) model. In the NPL model, ordered domains are formed by the lateral re gister of similar but non-periodic sequences of neighbouring chains, w hereas in the PCL model ordered domains are formed by the presence of conformational correlations between adjacent monomers without explicit sequence matching. The two models are compared in view of the experim ental observations about the structure and the morphology of the cryst allized material. This review ends with some conclusions. Copyright (C ) 1996 Elsevier Science Ltd.