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Kinetics of Rotational Motion in Liquid-Crystalline Polymers

W. Stille, G. R. Strobl. Polym. Sci. (Russia) 35, 1484 (1993)


The rotational viscosity γ1 of a liquid-crystalline side-group polymer depends on the temperature and the molecular mass and is always remarkably higher than for the equivalent low molecular mesogen. By measuring the rotational diffusion constant Dr of the mesogen side-groups through dielectric relaxation experiments while simultaneously determining γ1 in director reorientation experiments, it was possible to exactly analyze the temperature and molecular mass dependence. In general, γ1 is additively composed of a contribution γ1m, connected with the reorientation of the mesogen side-groups, and a second contribution Δγ1, combined with the synchronous redirection of the main chain. As in low molecular liquid crystals, γ1m is in inverse ratio to Dr and is related to the glass transition temperature by the Vogel-Fulcher-Tamann law. The dependence of Δγ1 on the molecular mass is described by a power law. Examinations were made on LC polymethacrylates of different molecular mass, as well as on LC polysiloxane-LC monomer mixtures. On the basis of an explicit equation γ1(M,T) it is possible to give a consistent description of the measured values.

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