Abstract Vapor–liquid equilibrium data for the poly(vinylpyrrolidone) (PVP) + NaH2PO4 + H2O system have been determined experimentally using the improved isopiestic method at 298.15, 308.15 and 318.15 K. The effect of temperature on the vapor–liquid equilibrium has been studied and compared with that on the liquid–liquid equilibrium of the aqueous PVP + NaH2PO4 two-phase system. It was found that the slope of constant water activity lines and tie-lines increased with increasing the temperature. The results have been discussed on the basis of the effect of temperature on the hydrophobicity of the polymer. Furthermore, the segment-based local composition Wilson model has been used for the correlation of the experimental water activity data. The agreement between the correlation and the experimental data is good. c 2005 Elsevier Ltd. All rights reserved.
