PREPARATION AND CHARACTERIZATION OF THERMOTROPIC LIQUID-CRYSTAL COPOLYESTERS CONTAINING M-HYDROXYBENZOIC ACID UNITS

Wholly aromatic, main-chain copolyesters derived from terephthalic aci d and phenylhydroquinone modified with m-hydroxybenzoic acid were prep ared and characterized by elemental analyses, C-13 nuclear magnetic re sonance, thermogravimetric analysis, optical observations, differentia l scanning calorimetry and wide-angle X-ray diffraction. The phases be haviours depended on copolymer composition. Poly(p-phenylphenylene ter ephthalate-co-m-hydroxybenzoate)s with molar percentages of the p-phen ylphenylene terephthalate units in excess 70 mol% displayed thermotrop ic mesophases at relatively low temperatures and exhibited good therma l stability up to about 400 degrees C. Increasing content of m-hydroxy benzoic acid units, which increased the amount of structural irregular ity, decreased the isotropization temperature and the temperature at w hich the melt started to flow, and also caused a loss of both crystall inity and of liquid crystallinity. Copyright (C) 1996 Elsevier Science Ltd.