MOLECULAR PACKING AND DYNAMICS OF THE MAIN-CHAIN AND SIDE-CHAINS IN MESOMORPHIC POLY(VINYL ETHER)S AS REVEALED BY X-RAY-SCATTERING, DIELECTRIC-SPECTROSCOPY, SOLID-STATE H-2, AND C-13-MAS NMR-SPECTROSCOPY

The conformational states and dynamics of a series of side-chain liqui d crystalline poly(vinyl ether)s with phenylbenzoate or stilbenzyloxy as mesogen and with 4-11 methylene spacer groups, where the 11-methyle ne-spacer polymers had two different tacticities, were assessed by die lectric and NMR spectroscopy. Dielectric spectroscopy confirmed the pr esence of three subglass processes (beta, gamma, and delta) exhibiting an Arrhenius temperature dependence. The activation energy (35 +/- 5 kJ/mol) of the gamma process was insensitive to the morphology, and th is process is assigned to localized motions within the spacer group. T he absence of the beta process in the stilbenzyloxy polymer suggests t hat this process is due to flips of the phenylene units causing a 180 degrees reorientation of the carboxylic group in the phenyl benzoate m oiety. The frequency of the flip of the inner phenylene unit at 0 degr ees C as obtained by C-13-MAS NMR was almost the same as the frequency of the dielectric beta loss peak at the same temperature. The relaxat ion strength of the beta process passed through a maximum as the space r length increased. It is suggested that the participating carboxyl gr oups were unable to reorient completely in a polymer with a short spac er group since reorientation of the mesogen was more complete in a pol ymer with longer spacer groups, the latter containing a smaller percen tage of mesogens. C-13-MAS NMR data indicated that the gauche content of the spacer group was lower than that of a free polymethylene chain at the same temperature and that it increased with increasing temperat ure. The X-ray scattering patterns of the 11-methylene-spacer polymers with different tacticities were identical, and it was shown by NMR an d dielectric spectroscopy that the molecular dynamics was not influenc ed by the tacticity of the polymers. The decrease in the thickness of the smectic layer at the transition from smectic B to smectic A is acc ompanied by a pronounced increase in segmental mobility of the backbon e as revealed by H-2 NMR spectroscopy.