WHOLLY AROMATIC THERMOTROPIC LIQUID-CRYSTALLINE POLYESTERS OF 2-(ALPHA-PHENYLISOPROPYL)HYDROQUINONE - COPOLYMERS WITH 1,1'-BIPHENYL-4,4'-DIOL AND 2,6-DIHYDROXYNAPHTHALENE

Two series of new aromatic copolyesters have been synthesized and thei r properties including liquid crystallinity have been studied. The fir st series was synthesized by polymerizing mixtures of diacetates of 2- (alpha-phenylisopropyl)hydroquinone and 1,1'-biphenyl-4,4'-diol with t erephthalic acid, and the second by polymerizing mixtures of diacetate s of 2-(alpha-phenylisopropyl)hydroquinone and 2,6-dihydroxynaphthalen e with terephthalic acid. These polyesters were characterized by diffe rential scanning calorimetry, thermogravimetric analysis, wide-angle X -ray diffractomerty, and optical microscopy. The glass transition temp eratures of the first series decrease from 167 to 138 degrees C as one increases the content of the 1,1'-biphenyl-4,4'-diol unit to 50 mol % . The T-g values of the second series are slightly higher than those o f the first series, and appear to be less dependent on their compositi on. The degree of crystallinity of the first series decreases rapidly by copolymerization, much faster than that of the second series. The m elting points of the first series copolymers are significantly lower t han those of the second series. All of the copolyesters reported in th is investigation form nematic melts. The initial decomposition tempera tures of the copolymers were higher than 450 degrees C. It was confirm ed that thermal stability of the homopolyester, PIBPL-1.00, containing the isopropylidene units is significantly improved when compared with that carrying benzylic hydrogens. (C) 1997 John Wiley & Sons, Inc.