New PET-Based Liquid Crystalline Copolyesters and Their Use in Blends and Composites

Abstract

New liquid crystalline copolyesters have been synthesized by melt transesterification of poly(ethylene terephthalate), p(ET), with 4-acetoxybenzoic acid (H), and varying proportions of equimolar mixtures of diacetylated 4,4′-dihydroxybiphenyl (B) and terephthalic acid (T). The solidification of the polymerizing mixture due to segregation of a highly aromatic crystalline phase, which limited the available range of compositions when p(ET) was modified with H only, was shown not to take place when moderate amounts of T and B were added to H. The p(ETHB) copolyesters are shown to posses high structural homogeneity, even when the content of p(ET) in the starting mixture is as low as 10 mol-%. The thermal properties of the copolyesters can be changed in a fairly wide range by varying the chemical composition. As a result, the properties of the new LCPs can easily be optimized in view of different applications, such as the production of blends with flexible thermoplastics or of glass fiber-reinforced composites.