EFFECTS OF CONCENTRATION AND THERMODYNAMIC INTERACTION ON THE VISCOELASTIC PROPERTIES OF POLYMER-SOLUTIONS

We report linear viscoelastic measurements for solutions of a high molecular weight polybutadiene covering the entire range of concentration from pure polymer to pure solvent at 25-degrees-C. Two solvents were employed that have glass transition temperatures near that of polybutadiene: dioctyl phthalate is nearly a THETA-solvent at 25-degrees-C and phenyloctane is a good solvent. We find three regimes of concentration for the viscosity in each solvent. In dilute solution (phi < phi*) the viscosities are well represented by the Huggins equation, although with quite different intrinsic viscosities and Huggins coefficients in the two solvents. In the entangled semidilute range (phi-c < phi < 0.1) and the concentrated regime (phi > 0.1) the free volume adjusted viscosity is identical in the two solvents and obeys power laws of phi-4.7 in semidilute solution and phi-3.6 in concentrated solution. Elastic response is also identical for the two solvents, with G-degrees-N (inferred from G"m) proportional-to 1/J-degrees-e proportional-to phi-2.3 for phi > 0.02. The results in semidilute solution compare favorably with the predictions of a recent two-parameter scaling theory. The observations also suggest that the concentration dependences of the characteristic molecular weights M(e) and M(c) are somewhat different.