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 non-mesogenic main chain segments on the mesomorphic properties a series of new liquid crystalline polyesters with 4-(4-nitrobenzyloxy)biphenyl moieties as mesogenic side groups was prepared. The mesomorphic and dynamic behavior were investigated by means of differential scanning calorimetry (DSC), X-ray measurements, polarization microscopy and dielectric spectroscopy. All polyesters exhibit nematic and different smectic phases. Some of the homologues show “re-entrant” nematic phases. The clearing point decreases at first with increasing main chain spacer length and passes through a minimum. From the results it was possible to propose packing models of the smectic phases with low order.