New PET-based liquid crystalline copolyesters and their use in blends and composites

New liquid crystalline copolyesters have been synthesized by melt transeste rification of poly(ethylene terephthalate), p(ET), with 4-acetoxybenzoic ac id (H), and varying proportions of equimolar mixtures of diacetylated 4,4 ' -dihydroxybiphenyl (B) and terephthalic acid (T). The solidification of th e polymerizing mixture due to segregation of a highly aromatic crystalline phase, which limited the available range of compositions when p(ET) was mod ified with H only, was shown not to take place when moderate amounts of T a nd B were added to H. The p(ETHB) copolyesters are shown to posses high str uctural 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 c hanged in a fairly wide range by varying the chemical composition. As a res ult, the properties of the new LCPs can easily be optimized in view of diff erent applications, such as the production of blends with flexible thermopl astics or of glass fiber-reinforced composites.