Concentrated Solution Viscosity Behavior at Elevated Temperatures—Polystyrene in Ethylbenzene

The viscosity behavior of polymer solutions at high concentrations and elevated temperatures is of scientific and technological importance. Nonetheless, few data covering this regime are extant, due in part to the difficulty of making the appropriate measurements. A new capillary rheometry method using a pressurized exit chamber, described by the author in a previous paper, was used to obtain a systematic body of viscosity data for the system polystyrene–ethylbenzene at elevated temperatures (60–255°C) and high concentrations (40–100% polymer). The temperature dependence of viscosity was representable in terms of flow curve shear rate‐temperature superposition over the entire concentration range investigated, with the shift factor temperature dependence being quantitatively described by an Arrhenius‐type relation at temperatures well above $Tg,$ yielding energies of activation for viscous flow as a well‐defined function of concentration over the entire concentration range. The concentration dependence of the Newtonian limiting viscosities was evaluated over the 40–100% range at both isothermal and isofree volume conditions. This observed dependence was considerably more severe than that projected from results in the literature obtained at lower concentrations and closer to $Tg.$