Abstract
The kinetics of crystallization from the mesophase and liquid crystallization from an isotropic melt of fractions of an aromatic thermotropic polyester were investigated by differential scanning calorimetry and depolarizing transmittance measurements. The isothermal process of these transitions can be described by the Avrami equation. The values of the exponent n are found to be ∼4 and ∼1 for crystallization and liquid-crystallization transitions, respectively. The temperature dependence of the crystallization rate from the mesophase is similar to that for small-molecule liquid crystals and also to that for conventional polymers obtained from an isotropic melt. Compared to crystallization, the liquid-crystallization rate shows a very weak temperature dependence. This implies that the surface free energy of mesophase domains is much less than that of crystallites, which may explain the experimental fact that liquid crystallization from an isotropic melt can proceed with high transformation rate at very small undercoolings, whereas crystallization only proceeds at very large undercoolings.
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