MIXING ENTHALPY AND PHASE-SEPARATION IN A POLY(PROPYLENE OXIDE)-WATERSYSTEM

Calorimetric measurements of the differential enthalpies of mixing a p ropylene oxide oligomer and water at two temperatures have been perfor med and the integral mixing enthalpies were found to be exothermic. Th e measurements were compared with the predictions of an extended Flory -Huggins model and a semiquantitative agreement was found. The model s uggests that the origin of the exothermic mixing is a conformational c hange of the propylene oxide oligomer from less polar and higher-energ y conformers to more polar and lower-energy conformers upon mixing wit h water.