The various dipolar relaxation mechanisms of a liquid-crystalline side-chain polymer have been studied in detail by the technique of thermally stimulated currents. The ~ relaxation, or glass transition relaxation, showed a compensation behaviour, i.e. a correlation between the activation enthalpy and the activation entropy of its components. Two sub-glass relaxations were observed. The lower-temperature one shows a small activation enthalpy (5-6 kcal mol- ~), and is attributed to slightly hindered internal rotations in the side group. The higher-temperature one, on the other hand, shows a higher activation enthalpy (23 kcal 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 main-chain segments. An upper glass relaxation was also observed. This relaxation shows a Williams-Landel-Ferry or Vogel behaviour and high values of its mean activation enthalpy and entropy. The attribution of this discharge at the molecular level is discussed
Посилання на статтю:
The dipolar relaxation behaviour of a liquid-crystalline side-chain polymer as studied by thermally stimulated discharge currents / Joao F. Mano and Joaquim J. Moura Ramos and Anabela Fernandes // Polymer. – 1994. – Vol 35. – P. 5170-5178.