A local composition model is developed for the representation of the excess Gibbs energy of polymer solutions. The model consists of two contributions due to the configurational entropy of mixing, represented by the Freed Flory–Huggins relation, and to the enthalpic contribution, represented by local compositions through nonrandom factor. The model is applied to correlate the solvent activity of binary polymer solutions. The new excess Gibbs energy equation was used along with the absolute rate theory of Eyring for modeling the dynamic viscosity of binary polymer solutions in the entire concentration range at different temperatures considering different molar mass of polymers. The fitting quality of new model has favorably been compared with polymer-NRTL, segment-based-liquid-NRTL, polymer-Wilson, polymer-NRF and polymer-NRF-Wilson models. The validity of the proposed model is especially demonstrated for the whole range of polymer concentrations at different temperatures using different molar masses of po...