LIQUID-CRYSTALLINE AROMATIC POLYESTERS CONTAINING ISOPHTHALIC ACID

We have synthesized a series of copolyesters and terpolyesters containing the isophthalate unit in order to study the implications of nonlinear polymer backbones on liquid crystallinity. Copolyesters were prepared from isophthalic acid, hydroquinone, and terephthalic acid by melt polymerization. Poly(p-phenylene terephthalate-co-p-phenylene isophthalate)s with molar percentages of the p-phenylene isophthalate repeat unit ranging from 75 to 95 mol % exhibit melting temperatures near 350 degrees C. The copolyester with 85 mol % of p-phenylene isophthalate exhibits a melting temperature of 355 degrees C and a mesophase range of 30 degrees C. Thermal properties of terpolyesters composed of four monomer units (isophthalic acid, hydroquinone, terephthalic acid, and p-hydroxybenzoic acid) show optimal compositions with melting temperatures below 350 degrees C and wide mesophase ranges. Our findings show that high contents of nonlinear monomers may be incorporated into polyesters without deleterious effects on liquid crystallinity in a composition range that can be processed at reasonable temperatures.