Ber. Bunsenges. Phys. Chem. 97, 1315 (1993)

Molecular Weight Dependence of the Rotational Diffusion Constant and the Rotational Viscosity of Nematic Side-Group Polymers

S. Götz, W. Stille, G. Strobl

Fakultät für Physik, Universität Freiburg, Hermann-Herder-Straße 3, D-79104 Freiburg

H. Scheuermann

Institut für Makromolekulare Chemie, Universität Freiburg, D-79104 Freiburg


A combination of dielectric relaxation spectroscopy and measurements of the rotational viscosity by director reorientation experiments was used to study nematic side-group polymethacrylates with different molecular weight. The contribution γ1m of the mesogenic groups to the total rotational viscosity γ1t is estimated on the base of Marrucci's theory from the rotational diffusion constant Dr obtained by relaxation frequency determinations. γ1m then is used to separate the contribution Δγ1 of the friction due to rearrangements of anisotropic ordered polymer backbones to γ1t. 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.