Synthesis and properties of copolyesters based on hydroquinone, sebacic acid and p-hydroxybenzoic acid

A series of thermotropic liquid crystalline copolyesters were prepared by a melt-polycondensation of 1,4-diacetoxybenzene (HQ) and sebacic acid (SA) w ith various amounts of p-acetoxybenzoic acid (HBA) in the presence of p-tol uene sulfonic acid as a catalyst. The chemical structure, phase transition behaviours, liquid crystallinity and thermal stability were examined by Fou rier transform infrared absorption spectroscopy, H-1 nuclear magnetic reson ance, differential scanning calorimetry, thermogravimetry and polarized-lig ht microscopy. With increasing HBA content, the glass transition temperatur e and melting temperature increased slightly, while the crystallinity decre ased significantly. The copolyesters with HBA contents higher than 30 mol% could show a nematic phase and their isotropization temperatures increased markedly with increasing HBA content. The environmental degradability has b een ascertained by testing the resistance of copolyester films to both alka line hydrolysis and activated sludge. The degradation rate and the extent o f the hydrolysis of the above copolyesters were evaluated by their weight l osses. Weight loss and scanning electron microscope observation could not e xhibit any significant change in the activated sludge during the test perio d, while the copolyesters with HBA contents higher than 30 mol% showed a dr amatical weight loss in alkaline aqueous solution.