Crystallization of thermotropic liquid crystalline HBA/HNA copolymers

The crystallization behaviour of random copolymers based on p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) is reviewed. First a summary is given of what is known about the structure and thermal transitions of the constituent homopolymers. Next the crystallization behaviour of HBA/HNA copolymers is described starting with the glass transition, after which the two crystallization processes that have been found in these copolyesters are treated. The crystallization of the HBA/HNA copolymers will be compared to the crystallization of similar random copolymers that are not liquid crystalline. Two models have been proposed to describe the solid state of the HBA/HNA copolymers: the non-periodic layer (NPL) model and the paracrystalline lattice (PCL) model. In the NPL model, ordered domains are formed by the lateral register of similar but non-periodic sequences of neighbouring chains, whereas 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 experimental observations about the structure and the morphology of the crystallized material. This review ends with some conclusions. Copyright (C) 1996 Elsevier Science Ltd.