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By means of capillary and rotational viscometers flow curves of concentrated polystyrene solutions were obtained. The measurements were carried out at concentrations of 0.184–0.573 volume fraction of polymer, shear stresses of 3 × 101−3 × 106 dyne/cm.2, shear rates of 1 × 10−6 to 1 × 106 sec.−1, and temperatures of 15–120°C. It was shown that both the deterioration of quality of solvent and the decrease of temperature increase the initial Newtonian viscosity and facilitates attainment of the upper Newtonian viscosity. The influence of the chemical nature of the solvent on the viscosity of the solution appeared stronger in the higher regions of shear stress and shear rate, that is, at the transition from the initial Newtonian viscosity to the upper Newtonian viscosity. This regularity was explained by the presence of two kinds of structural formation in concentrated polymer solutions: bundles of polymer chains and fluctuational networks composed of the bundles. The bundles can be dissociated in different degrees by good and poor solvents. The paper considers the application of some of the reduction methods to the experimental data.

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