INVESTIGATION OF PHASE-TRANSITION IN MAIN-CHAIN LIQUID-CRYSTALS - POLY[TRIS(OXYMETHYLETHYLENE) HENYLENEOXYTEREPHTHALOYLOXY-1,4-PHENYLENECARBONYL]

Thermal transitions in a new main chain liquid crystal polymer, poly[t ris(oxymethylethylene) nyleneoxy-terephthaloyloxy-1,4-phenylenecarbony l], PTOPTO, have been studied by differential scanning calorimetry, op tical microscopy and wide-angle X-ray diffraction, employing synchrotr on radiation. The thermal behaviour of this polymer is very complex an d includes four main transitions at 36, 70, 141 and 176 degrees C, ass ociated with the glass transition, a smectic S-C to S-A transition, a change from smectic S-A to the nematic phase and the isotropization te mperature, respect ively. Changes in the structure from fan-shaped to focal conic structures confirm the transition from S-C to S-A and the appearance of Williams domains confirm the transition from S-A to nema tic. These observations coincide with the data obtained by X-ray diffr action, in which a shift in the peak at 2 theta=3.35 degrees is detect ed. Reflections associated with three-dimensional order were not obser ved, due to the asymmetry of the spacer. (C) 1997 Elsevier Science Ltd .