X-RAY-ANALYSIS OF THE STRUCTURE OF A THERMOTROPIC MAIN-CHAIN LIQUID-CRYSTALLINE COPOLYESTER

The structure and phase behaviour of the thermotropic main-chain liqui d-crystalline copolyester nylene)-co-(terephthalate)-co-(p-hydroxybenz oate)] (PES) prepared from terephthalic acid, phenylhydroquinon and p- hydrobenzoic acid (molar ration 45/45/10) is determined by X-ray diffr action and differential scanning calorimetry. This random copolyester shows up to 340 degrees C periodic c-axis order in its X-ray diffracti on; pattern as well as sharp and diffuse reflections at the equator an d other crystallographic directions, indicating well ordered three-dim ensional crystalline structure. Two crystalline modifications are obse rved for quenched and annealed fibres, which are both orthorhombic wit h slightly different unit cell sizes. Indications of other phases at s tilt higher temperatures are reported. They are believed to be a novel mesophase followed by a nematic liquid-crystalline phase and the isot ropic melt.