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.

Thermodynamic properties of aqueous polypropylene oxide 400 solutions from isopiestic measurements over a range of temperatures

“…This is because the PPO becomes more hydrophobic with increasing temperature. The solubilities of PPO in water [10], mixing enthalpies [10] and excess molar volume [35] of PPO in water support this interpretation. It was found that the solubility of PPO in water decreases with increasing temperature [10].…”

“…The solubilities of PPO in water [10], mixing enthalpies [10] and excess molar volume [35] of PPO in water support this interpretation. It was found that the solubility of PPO in water decreases with increasing temperature [10]. Carlsson et al [10] measured mixing enthalpy of PPO in water at two temperatures and showed that the excess enthalpy of this system is negative and decrease in magnitude as temperature increases.…”

“…It was found that the solubility of PPO in water decreases with increasing temperature [10]. Carlsson et al [10] measured mixing enthalpy of PPO in water at two temperatures and showed that the excess enthalpy of this system is negative and decrease in magnitude as temperature increases. Similar to the excess enthalpy, Zafarani-Moattar et al [35] showd that the excess volume of the PPO + water system is Table 5 Activity of water (a 1 ), vapor pressure (p), osmotic coefficient (Φ), activity coefficient of water (γ 1 ) and activity coefficient of polymer (γ 2 ) for PPO 400 (2) Table 6 Activity of water (a 1 ), vapor pressure (p), osmotic coefficient (Φ), activity coefficient of water (γ 1 ) and activity coefficient of polymer (γ 2 ) for PPO 400 (2) ative values of both excess volume and excess enthalpies are obtained.…”

“…(12) and obtained parameters, the excess molar enthalpies of aqueous solution of PPO 400 at different temperatures have been predicted and shown in Fig. 8 along with the experimental results for excess molar enthalpies of PPO 400 − H 2 O at 298.15 and 321.15 K [10]. As can be seen from Fig.…”

“…A typical feature of polypropylene oxide (PPO) and polyethylene oxide (PEO) as well as copolymers of PO and EO is their reduced solubility in aqueous solution with increasing temperature. Much of the interest in these copolymers is rooted in the possibility that the solubility and other solution thermodynamic properties may be varied and optimised for various applications by appropriate choice of the relative proportions of PO and EO units in the chains [10].…”