Abstract
A series of thermotropic liquid crystalline copolyesters were prepared by a melt-polycondensation of 1,4-diacetoxybenzene (HQ) and sebacic acid (SA) with various amounts of p-acetoxybenzoic acid (HBA) in the presence of p-toluene sulfonic acid as a catalyst. The chemical structure, phase transition behaviours, liquid crystallinity and thermal stability were examined by Fourier transform infrared absorption spectroscopy, 1H nuclear magnetic resonance, differential scanning calorimetry, thermogravimetry and polarized-light microscopy. With increasing HBA content, the glass transition temperature and melting temperature increased slightly, while the crystallinity decreased 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 been ascertained by testing the resistance of copolyester films to both alkaline hydrolysis and activated sludge. The degradation rate and the extent of the hydrolysis of the above copolyesters were evaluated by their weight losses. Weight loss and scanning electron microscope observation could not exhibit any significant change in the activated sludge during the test period, while the copolyesters with HBA contents higher than 30 mol% showed a dramatical weight loss in alkaline aqueous solution.
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