Mixing enthalpy and phase separation in a poly(propylene oxide)–water system

Abstract

Calorimetric measurements of the differential enthalpies of mixing a propylene oxide oligomer and water at two temperatures have been performed and the integral mixing enthalpies were found to be exothermic. The measurements were compared with the predictions of an extended Flory–Huggins model and a semiquantitative agreement was found. The model suggests that the origin of the exothermic mixing is a conformational change of the propylene oxide oligomer from less polar and higher-energy conformers to more polar and lower-energy conformers upon mixing with water.