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Vapor−liquid equilibria P, T, x for the methanol + poly(ethylene glycol) 250 dimethyl ether (PEGDME 250) binary system were obtained by the static method in the range of temperatures from 293.15 K to 423.15 K at 10 K intervals. A modified Barker's method was used to accurately calculate the liquid and vapor composition from the overall composition of the sample, the measured pressure and temperature, and the Redlich−Kister expression for the excess Gibbs free energy of the liquid phase at each temperature. The obtained P, T, x data were correlated by the NRTL and UNIQUAC temperature-dependent activity coefficient models using the maximum likelihood method. This system shows nearly ideal behavior at lower temperatures but negative deviation at higher temperatures. Also with the increase in temperature and composition of poly(ethylene glycol) 250 dimethyl ether, the logarithm of activity coefficients of methanol becomes more negative. The excess molar enthalpy was calculated using the Gibbs−Helmholtz equation and the NRTL and UNIQUAC parameters at 303.15 K and compared with experimental data existing in the literature.

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