DIELECTRIC-RELAXATION OF LIQUID-CRYSTALLINE SIDE-CHAIN POLY(VINYL ETHER)S

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 mes omorphic side-chain poly(vinyl ether)s, -(11-(vinyloxy)undecyloxy)-4-e thoxyphenylbenzoate) (P-EtO) and 4-(11-(vinyloxy)undecyloxy)-4-cyanoph enylbenzoate) (P-CN) of different degree of mesogen group orientation. X-ray scattering showed that P-EtO was in a semicrystalline state bel ow 345 K, whereas P-CN displayed a tilted smectic structure at tempera tures lower than 315 K. Four relaxation transitions were found in P-Et O: alpha, the glass-rubber transition occurring at 290-300 K, and thre e subglass processes referred to as beta, gamma and delta. P-CN exhibi ted only three dielectric processes, alpha, beta and gamma. The low te mperature process, delta, was absent in P-CN and could be assigned to torsion about the pendent phenyl-carbon-ether-oxygen bond. Subglass pr ocesses beta and gamma exhibited an Arrhenius temperature dependence w ith activation energies of 60-105 and 32 +/- 2 kJ mol-1, respectively. The activation energy of the gamma process was insensitive to morphol ogy and it was assigned to local motions in the spacer group. The acti vation energy of the beta process varied considerably among the studie d polymers with higher values for the highly ordered P-EtO than for P- CN. It is suggested that the beta process leads to reorientation of th e carboxylic group in the phenyl benzoate moiety.