Rheology of a Comblike Liquid Crystalline Polymer as a Function of Its Molecular Weight

We have performed rheological studies on a nonentangled comblike liquid crystalline polymer. Fractionated samples of six different molecular weights and a nonfractionated sample (large molecular weight distribution) were studied. The storage and loss moduli, G ‘ and G ‘‘, were measured as a function of frequency for different temperatures, in the isotropic phase for the fractionated samples and in both isotropic and nematic phases for the nonfractionated one. They were found to obey time/temperature superposition in both phases. At intermediate frequencies, G ‘ and G ‘‘ obeyed a frequency power law: G ‘ ∼ G ‘‘ ∼ ω 0.6 . At low frequencies in the isotropic phase, the zero-shear rate viscosity, η 0, and an average terminal time, τ ter, were measured as a function of molecular weight. The power laws obtained are: η 0 ∼ M w 1.3 ± 0.1 and τ ter ∼ M w 2.6 ± 0.3 . These results are discussed in the frame of the classical Rouse model for free chains. Possible effects of interactions between the teeth of the combs are also considered.