Dielectric permittivity and loss have been measured over the frequency range 10-2 Hz-10 kHz between 100 K and 350 K for samples of two mesomorphic side-chain poly(vinyl ether)s, poly(4-(11-(vinyloxy)undecyloxy)- 4-ethoxyphenylbenzoate) (P-EtO) and poly(4-(11-(vinyloxy)undecyloxy)-4-cyanophenylbenzoate) (P-CN) of different degree of mesogen group orientation. X-ray scattering showed that P-EtO was in a semicrystalline state below 345 K, whereas P-CN displayed a tilted smectic structure at temperatures lower than 315 K. Four relaxation transitions were found in P-EtO: ~, the glass-rubber transition occurring at 290-300 K, and three subglass processes referred to as/~, 7 and 6. P-CN exhibited only three dielectric processes, ~,/~ and 7. The low temperature process, 6, was absent in P-CN and could be assigned to torsion about the pendent phenyl-carbon-ether-oxygen bond. Subglass processes/~ and 7 exhibited an Arrhenius temperature dependence with activation energies of 60-105 and 32+ 2 kJmol-1, respectively. The activation energy of the 7 process was insensitive to morphology and it was assigned to local motions in the spacer group. The activation energy of the/~ process varied considerably among the studied polymers with higher values for the highly ordered P-EtO than for P-CN. It is suggested that the/~ process leads to reorientation of the carboxylic group in the phenyl benzoate moiety.
Посилання на статтю:
Dielectric relaxation of liquid crystalline side-chain poly(vinyl ether)s / U. W. Gedde*, F. Liut, A. Hult, F. Sahl6n and R. H. Boyd // Polymer. – 1994. – Vol 35. – P. 2056-2062.