Inverse gas chromatography (IGC) was used to measure various thermodynamic properties (activity coefficients, Flory-Huggins interaction parameters, partial molar heats of mixing, heats of solution, and heats of vaporization) at infinite dilution for polymer solution systems. The experimental temperature ranges were from 353.15 K to 463.15 K and they were carried out over melting point or glass transition temperature of each polymer. The solvent(1)/polymer(2) systems were made up of polyethyleneglycol, polymethylemthacrylate, and poly(ethylene(80)-vinylacetate(20)) as the polymers, polar solvents (methylethylketone, n-butylacetate, butanol, ethylacetate, chloroform, methanol, toluene, ethanol, 1,4-dioxane, ethylbenzene, methylisobutylketone) and nonpolar solvents (acetone, benzene, carbontetrachloride, cyclohexane, p-xylene, n-decane) as the solvents. The UNIFAC-FV model was modified to predict the partial molar heat of mixing the solvents at infinite dilution for polymer solution systems. The modified UNIFAC-FV model included the external degree of freedom, which is a function of temperature, and had the new parameters, which were estimated by the infinite dilution activity coefficients of solvents in polymer solutions. The calculated activity coefficients of solvents agreed with the experimental data within an error average range of 1.09 (2.12%). The new estimated parameters were extended to predict the partial molar heats of mixing the solvents at infinite dilution in polymer solutions. The predicted values were compared with the experimental data.