RHEOLOGY OF A COMB-LIKE LIQUID-CRYSTALLINE POLYMER AS A FUNCTION OF ITS MOLECULAR-WEIGHT

We have performed rheological studies on a nonentangled comblike liqui d crystalline polymer. Fractionated samples of six different molecular weights and a nonfractionated sample (large molecular weight distribu tion) were studied. The storage and loss moduli, G' and G '', were mea sured as a function of frequency for different temperatures, in the is otropic phase for the fractionated samples and in both isotropic and n ematic phases for the nonfractionated one. They were found to obey tim e/ temperature superposition in both phases. At intermediate frequenci es, G' and G '' obeyed a frequency power law: G' similar to G '' simil ar to omega(0.6). At low frequencies in the isotropic phase, the zero- shear rate viscosity, eta(o), and an average terminal time, tau(ter), were measured as a function of molecular weight. The power laws obtain ed are: eta(o) similar to M-w(1.3 +/- 0.1) and tau(ter) similar to M-w (26+/-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.