MOLECULAR-WEIGHT DEPENDENCE OF THE ROTATIONAL DIFFUSION CONSTANT AND THE ROTATIONAL VISCOSITY OF LIQUID-CRYSTALLINE SIDE-GROUP POLYMERS

Nematic side-group polymethacrylates with different molecular weights were studied by a combination of dielectric relaxation spectroscopy and measurements of the rotational viscosity by director reorientation experiments. The rotational diffusion constant obtained by relaxation frequency determinations allows the estimation of the contribution gamma1m of the mesogenic groups to the total rotational viscosity gamma1t on the basis of Marrucci's theory. Gamma1m then is used to separate the contribution DELTAgamma1 of the friction due to rearrangements of anisotropic ordered polymer backbones to gamma1t. The molecular weight dependence of DELTAgamma1 can be described by a power law, as predicted by Brochard's theory. The resulting exponent gives evidence for the presence of nonentangled random-coil conformations. A model for the director reorientation shows the possibility of biexponential time dependencies for systems containing flexible chains with anisotropic conformations.