TEMPERATURE EVOLUTION OF THE STRUCTURE OF A THERMOTROPIC MAIN-CHAIN LIQUID-CRYSTALLINE COPOLYESTER

X-ray diffraction, differential scanning calorimetry and dynamic mecha nical analysis are used to study the temperature evolution of the stru cture of the thermotropic copolyester nylene)-co-(terephthalate)-co-(p -hydroxybenzoate)] (PES) prepared from terephthalic acid, phenyl-hydro quinone and p-hydroxybenzoic acid (molar ratio 45/45/10). Needle-like crystals are developed in the quenched as-spun fibers despite the rand om sequence of the monomers of the copolyester. Moreover, two other cr ystalline phases are observed at elevated temperatures, which may be e xplained by a phase separation process. X-ray diffraction experiments show a significant temperature dependence of structural features, indi cating some conformational disorder and mobility in this class of ''ri gid-rod' liquid crystalline prolymers. Changes in the X-ray pattern ar e observed on heating, starting immediately above the glass transition temperature of the copolyester. Melting of PES reveals a two-step cha racter with transitions at 300-degrees-C and 320-degrees-C. The materi al becomes isotropic at 400-degrees-C or higher.