TRANSITION KINETICS OF SMECTIC LIQUID-CRYSTALLINE POLYESTERS

Two smectic main-chain liquid-crystalline polyesters containing biphenyl as mesogen and spacers with 8 and 18 methylene carbon atoms were prepared, and their transition kinetics were investigated by means of differential scanning calorimetry (DSC). The isothermal liquid-crystallization was analyzed using the Avrami equation. The Avrami exponent n was found to be 2 to 4 indicating that the liquid-crystallization of these two smectic polyesters would be a process of two-to three-dimensional growth rather than of one-dimensional growth as for nematic liquid-crystalline polymers. The nonisothermal liquid-crystallization and crystallization were also analyzed by means of DSC. The crystallization from the smectic phase was found to be a very fast process and the supercooling of crystallization was small. Thus, the smectic phase might nucleate crystallization. The transition kinetics of these two smectic polyesters are considerably different from those of nematic liquid-crystalline polymers due to the different orders of the liquid-crystalline phases.