COPOLYESTERS OF 4-HYDROXY-3-PHENYLBENZOIC ACID AND 4-HYDROXYBENZOIC ACID

Crystalline poly(3-phenyl-4-hydroxybenzoic acid) was prepared by polycondensation of 4-acetoxy-3-phenylbenzoic acid in solution at 320-degrees-C. Differential scanning calorimetry (d.s.c.) and wide angle X-ray scattering (WAXS) measurements indicate that this homopolyester forms a nematic melt between 345-degrees-C and 465-degrees-C. Five copolyesters of 4-hydroxybenzoic acid (HBA) and 4-hydroxy-3-phenylbenzoic acid (3-PhHBA) with varying molar composition were prepared by polycondensation in solution. One additional copolyester was prepared by polycondensation in bulk. H-1 n.m.r. spectroscopy revealed a significantly lower reactivity of the phenyl-substituted acetoxybenzoic acid. The influence of the molar composition on crystallinity, phase transitions and stability of the nematic mesophase was studied by d.s.c. and WAXS measurements and by optical microscopy. Heat distortion temperatures were determined by the penetration method. It was found that the copolyesters prepared in bulk and in solution possess quite different properties. Only the copolyester prepared in bulk forms a nematic melt above its melting point at 205 +/- 3-degrees-C.