Molecular Weight Dependence of the Rotational Diffusion Constant and the Rotational Viscosity of Liquid Crystalline Side Group Polymers

Abstract

Nematic side group polymethacrylates with different molecular weight were studied by 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 to estimate the contribution γ₁^m of the mesogenic groups to the total rotational viscosity γ₁^t on the base of Marrucci's theory. γ₁^m then is used to separate the contribution Δγ₁ of the friction due to rearrangements of anisotropic ordered polymer backbones to γ₁^t. The molecular weight dependence of Δγ₁ 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.