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

Segmental mobility between 100 and 350 It is reported for a series of mesomorphic side-chain poly(vinyl ether)s with 4-11 methylene carbon a toms in the spacer and phenyl benzoate and stilbenyloxy groups used as mesogens. A glass-rubber transition (alpha) appears in the vicinity o f 300 K. Three subglass processes, referred to as beta, gamma, and del ta obey the Arrhenius and Cole-Cole equations. The delta-process is pr esent only in polymers with flexible and dielectrically active tail gr oups, e.g., in polymers with an ethoxy group, in which case the proces s can be assigned to torsion about the pendant phenyl-carbon-ether-oxy gen bond. The activation energy (35 +/- 5 kJ . mol(-1)) of the gamma-p rocess is insensitive to the morphology and is assigned to local motio ns within the spacer. The activation energy of the beta-process varied considerably among the studied polymers (60 to 126 kJ . mol(-1)). The absence of the beta-process in the stilbenyloxy polymer suggests that this process is clue to reorientation of the carboxylic group in the phenyl benzoate moiety. The relaxation strength associated with the be ta-process passes through a maximum as the spacer length increases, In a polymer with a short spacer group, the participating carboxyl group is not able to reorient completely. In polymers with longer spacer gr oups, reorientation is more complete but the concentration of active m esogens is lower. Phenyl-benzoate polymers with 11 carbon atoms in the spacer, with different tacticities, exhibited the same dielectric rel axation behavior.