*Macromolecules* **26**, 1520
(1993)

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

## S. Götz, W. Stille, and G. Strobl

### Fakultät für Physik, Universität Freiburg, 79104 Freiburg,
Germany

### H. Scheuermann

### Institut für Makromolekulare Chemie, Universität Freiburg,
79104 Freiburg, Germany

#### 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 γ_{1}^{m} of the
mesogenic groups to the total rotational viscosity γ_{1}^{t}
on the base of Marrucci's theory. γ_{1}^{m} then is used to
separate the contribution Δγ_{1} of the friction due to
rearrangements of anisotropic ordered polymer backbones to
γ_{1}^{t}. The molecular weight dependence of Δγ_{1}
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.