AbstractThe Kelley‐Bueche free‐volume treatment of the viscosity of polymeric solutions has been applied to the previously reported data on poly(vinyl chloride)‐cyclohexanone solutions and to several other polymer‐diluent systems. It has been shown that the theoretical equations, based on the assumption of the additivity of free volumes of the components, are capable of predicting with remarkable accuracy the concentration, temperature, and molecular weight dependence of the viscosity of the investigated solutions over very large ranges of the va