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 °C. Two solvents were employed that have glass transition temperatures near that of polybutadiene: dioctyl phthalate is nearly a θ solvent at 25 °C and phenyloctane is a good solvent. We find three regimes of concentration for the viscosity in each solvent. In dilute solution (∅<4∅*) 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 (∅_c<∅< 0.1) and the concentrated regime (∅> 0.1) the free volume adjusted viscosity is identical in the two solvents and obeys power laws of ∅^{4 7} in semidilute solution and ∅^3.6 in concentrated solution. Elastic response is also identical for the two solvents, with G°_n (inferred from G″_m) ∝1/J°_e ∝ ∅^2,3 for ∅ > 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.