Thermal expansion of liquid crystalline polyesters having phenanthrene moieties. Simultaneous DSC-XRD method

Phase transition process of polyester from phenanthrene, poly(oxyheptamethy leneoxy-2,7-phenantrenedicarbonyl), a main chain type liquid crystalline po lymer, was investigated by simultaneous DSC-XRD measurements using the sync hrotron radiation facility (PF). Three exothermic DSC peaks were observed d uring cooling from the isotropic liquid state. These DSC peaks were assigne d to the transition from the isotropic liquid to the smectic A, that from t he smectic A to C, and that from the smectic C to the crystalline state, re spectively, as determined by XRD profiles. The rate of transition from the smectic A to C was very slow compared with the liquid crystalline transitio n and the crystallization. From the DSC-XRD results, the thermal expansion along c-axis in the crystal and smectic phases are 4.1.10(-4) and 1.4.10(-3 ) nm K-1, respectively.