THE DIPOLAR RELAXATION BEHAVIOR OF A LIQUID-CRYSTALLINE SIDE-CHAIN POLYMER AS STUDIED BY THERMALLY STIMULATED DISCHARGE CURRENTS

The various dipolar relaxation mechanisms of a liquid-crystalline side -chain polymer have been studied in detail by the technique of thermal ly stimulated currents. The ct relaxation, or glass transition relaxat ion, showed a compensation behaviour, i.e. a correlation between the a ctivation enthalpy and the activation entropy of its components. Two s ub-glass relaxations were observed. The lower-temperature one shows a small activation enthalpy (5-6 kcal mol(-1)), and is attributed to sli ghtly hindered internal rotations in the side group. The higher-temper ature one, on the other hand, shows a higher activation enthalpy (23 k cal mol(-1)) and a low positive activation entropy, and is attributed to restricted internal rotations of the side groups around bonds near the main chain, eventually in cooperation with the movements of the ma in-chain segments. An upper glass relaxation was also observed. This r elaxation shows a Williams-Landel-Ferry or Vogel behaviour and high va lues of its mean activation enthalpy and entropy. The attribution of t his discharge at the molecular level is discussed.