The viscosity of concentrated polymer solutions containing low molecular weight solvents

The zero shear rate viscosities of polystyrene/ethylbenzene solutions having polymer weight fractions ranging from 0.5 to 1.0 have been measured using a novel sealed rheometer cell over a temperature range of 50 to 200°C. The concentration and temperature dependence of the solution viscosity has been found to be well described by the relation η₀ = K c^aM_w ^3.4ζ(c, T) where the monomeric friction coefficient ζ is determined by the free volume of the solution. Following the procedure of Berry, the free volume parameters, α_f(c)/γ and T_∞ (c), and the fractional free volume, f(c,T)/γ, have been determined. After using these parameters to account for the concentration dependence of the friction coefficient, the concentration exponent a has been evaluated and found to be in reasonable agreement with the value of 3.4 obtained by Berry and Fox for other polymer/solvent systems. A comparison of the relative conributions made by the friction coefficient and the term c^3.4 to the overall concentration dependence of the viscosity of these highly concentrated solutions shows the friction coefficient to be the dominant factor