Based on the generalized Gibbs free energy model of the mixing of liquids established by this work, an equation which can satisfactorily describe the variations of polymer-solvent interaction parameter with the concentration and temperature in the polymer solutions is derived. It is composed of two parts, namely the contributions of enthalpy and entropy, and is the same as Koningsveld- Kleintijens' relation formally. But its entropy contribution χ~S is a complex function of concentration, rather than an arbitrary constant as proposed by Koningsveld. Some characters of the polymer solution can be well explained by this equation.

Key words: HIGHPOLYMER, SOLVENTS, INTERACTIONS, FREE ENERGY