Thermal transition of a wholly aromatic thermotropic liquid crystalline copolyester

A copolyester was prepared from p-hydroxybenzoic acid (HBA), 2,6-naphthalen e dicaboxylic acid (NDA), and hydroquinone (HQ). Thermal transition behavio r and the crystal structure of this copolyester were investigated by using polarized light microscopy (PLM), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD) after annealing at solid-phase poly merization conditions. A glass transition or newly ordered structure in the 270-290 degrees C range was observed on annealing at 260 degrees C, which increased with annealing time, attributed to mobility and reactive rearrang ement in amorphous regions. Broad and unclear WAXD profiles and multimeltin g behaviors were found on annealing at 280 degrees C, and explained by hexa gonal and orthorhombic lattice formation and transformation. A large increa se in melting temperature was observed only on annealing at a temperature ( 320 degrees C) near the crystal-nematic transition, suggesting annealing te mperatures near the melting point are required for sufficient mobility to a fford crystalline rearrangement via transesterification. (C) 1999 John Wile y & Sons, Inc.