Viscoelastic measurements on main-chain thermotropics

Rheological properties, determined by torsion experiments, of three main-chain thermotropics are investigated. Stable, time-independent measurements are obtained in two of these polymers, and the corresponding dynamic viscoelastic and first normal difference results are analysed. In the nematic state both storage and loss moduli scale as G′, G″ ∝ ω 1 2 , and no shear modulus associated with an entanglement network is detected. Recoverable compliances J 0 e, which are determined from steady-state N 1 values, are several orders of magnitude higher than those of isotropic polymers. For one of the polymers, the characteristic molecular weight between entanglements, M c, is determined from Newtonian viscosities of isotropic solutions. Although the molecular weight of our sample is above M c, viscoelastic measurements at temperatures corresponding to the nematic state show no vestige of the entanglement network