Jf. Mano et al., THE DIPOLAR RELAXATION BEHAVIOR OF A LIQUID-CRYSTALLINE SIDE-CHAIN POLYMER AS STUDIED BY THERMALLY STIMULATED DISCHARGE CURRENTS, Polymer, 35(24), 1994, pp. 5170-5178
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.