THERMAL PHASE-BEHAVIOR OF HOMOLOGOUS LIQUID-CRYSTALLINE SIDE-GROUP POLYESTERS IN DEPENDENCE ON THE POLYMETHYLENE MAIN-CHAIN SPACER LENGTH

With the aim to investigate the influence of a systematic variation of the length of flexible nonmesogenic main chain segments on the mesomo rphic properties a series of new liquid crystalline polyesters with 4- (4-nitrobenzyloxy)biphenyl moieties as mesogenic side groups was prepa red. The mesomorphic and dynamic behavior were investigated by means o f differential scanning calorimetry (DSC), X-ray measurements, polariz ation microscopy and dielectric spectroscopy. All polyesters exhibit n ematic and different smectic phases. Some of the homologues show ''re- entrant'' nematic phases. The clearing point decreases at first with i ncreasing main chain spacer length and passes through a minimum. From the results it was possible to propose packing models of the smectic p hases with low order.