Thermally crosslinkable thermotropic copolyesters: Synthesis, characterization, and processing

The synthesis, characterization, and processing of thermotropic copolymers composed of hydroxybenzoic acid (HBA), hydroxynaphthoic acid (HNA), and systematically varying amounts of hydroquinone (HQ) and crosslinkable 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 introduce covalent crosslinking between laterally adjacent macromolecules. 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 viscosity and transition from liquid-like to solid-like behaviour as the crosslinking proceeds. X-ray diffraction reveals the changes in local organization with increasing XTA content. The microstructures of the XTA-containing copolymers (up to 20% XTA) in the condensed state are similar to those seen in HBA/HNA copolymers.