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

A combination of dielectric relaxation spectroscopy and measurements o f the rotational viscosity by director reorientation experiments was u sed to study nematic.side-group polymethacrylates with different molec ular weight. The contribution gamma1m of the mesogenic groups to the t otal rotational viscosity gamma1t, is estimated on the base of Marrucc i's theory from the rotational diffusion constant D(r) obtained by rel axation frequency determinations. gamma1m then is used to separate the contribution DELTAgamma1 of the friction due to rearrangements of ani sotropic ordered polymer backbones to gamma1t. The molecular weight de pendence of DELTAgamma1 can be described by a power law, as predicted by Brochard's theory. The resulting exponent gives evidence for the pr esence of nonentangled random coil conformations.