Morphological and kinetic studies of phase transitions of a side-chain liquid crystalline polymer

The morphological changes of a side-chain liquid-crystalline polymethacryla te during isotropization and liquid-crystallization transitions were studie d by means of polarizing microscopy. These transitions were found to be com posed of the initiation of a new phase at local places of the old phase mat rix and the growth of the new phase: domains. The kinetics of the liquid-cr ystallization of the polymer from an isotropic melt to a smectic mesophase was also investigated. The isothermal process of the transition can be desc ribed by the Avrami equation. The values of the Avrami exponent were found to be around 2.6. which is lower than the value usually obtained for crysta llization transition of polymers, but larger than that reported for liquid- crystallization transition of main-chain polymers. These results may indica te the difference in growth geometry of new phase during transition between crystallization and liquid-crystallization in general and between liquid-c rystallization of main-chain and side-chain polymers. It was found that the liquid-crystallization of the used side-chain polymethacrylate may occur a t small undercoolings with high transformation rate similar to that of main -chain polymers and small-molecule liquid crystals, while the crystallizati on of polymers can only proceed at large undercoolings. These phenomena can be explained by the idea that the surface free energy of nucleus during li quid-crystallization transition is less than that for crystallization, and evidence was obtained from analysis of the temperature dependence of the tr ansformation rate.