VISCOELASTIC MEASUREMENTS ON MAIN-CHAIN THERMOTROPICS

Rheological properties, determined by torsion experiments, of three ma in-chain thermotropics are investigated. Stable, time-independent meas urements 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'' is -proportional-to omega1/2, and no shear modulus associated with an ent anglement network is detected. Recoverable compliances J(e)0, which ar e determined from steady-state N1 values, are several orders of magnit ude higher than those of isotropic polymers. For one of the polymers, the characteristic molecular weight between entanglements, M(c), is de termined from Newtonian viscosities of isotropic solutions. Although t he molecular weight of our sample is above M(c), viscoelastic measurem ents at temperatures corresponding to the nematic state show no vestig e of the entanglement network.