THERMALLY CROSS-LINKABLE THERMOTROPIC COPOLYESTERS - SYNTHESIS, CHARACTERIZATION, AND PROCESSING

The synthesis, characterization, and processing of thermotropic copoly mers composed of hydroxybenzoic acid (HBA), hydroxynaphthoic acid (HNA ), and systematically varying amounts of hydroquinone (HQ) and crossli nkable terephthalic acid (XTA) are described. The XTA monomer contains a benzocyclobutene (BCB) group that lies dormant during synthesis and initial steps of processing, but that can be thermally activated to i ntroduce covalent crosslinking between laterally adjacent macromolecul es. The XTA-containing HBA/HNA copolymers all remain thermotropically liquid crystalline, and can be processed into oriented fibres by melt spinning. Rheological characterization reveals an increase in the visc osity and transition from liquid-like to solid-like behaviour as the c rosslinking proceeds. X-ray diffraction reveals the changes in local o rganization with increasing XTA content. The microstructures of the XT A-containing copolymers (up to 20% XTA) in the condensed state are sim ilar to those seen in HBA/HNA copolymers. (C) 1997 Elsevier Science Lt d.