| Abstract: | A new series of aromatic polyesters in which the polymethylene flexible spacers are connected with the rigid main chain containing benzene ring were prepared by interfacial polycondensation. The polymers were characterized by hotstage polarized microscopy, differential scanning calorimetry, wide-angle X-ray diffraction and Fourier-transform infrared spectroscopy. The structure and properties of polyesters were investigated. The results showed that the textures of the thermotropic liquid-crystalline polyesters are smectic and/or nematic. The dependence of melting point, clearing point and transition enthalpy of polyesters on length of the alkylene group revealed a regular zig-zag trend. The thermal analysis of polyesters revealed that the clearing transition is an equilibrium process, so the entropy of this transition may be taken as an indication of the degree of the order in mesomorphic state presented in the system. Furthermore, the thermal history of polymer had a significant effect on its thermal behavior. The regular arrangement of methylene segments changed when polymer melted from the crystal state to the liquid-crystalline state. The research also implicated that the conformational change of the methylene flexible spacer was one of the reasons for this thermal effect. |
