Poly(ethylene oxide) hydration studied by differential scanning calorimetry

Abstract

Differential scanning calorimetry has been used to investigate the melting behaviour of mixtures of poly(ethylene oxide) and deuterium oxide. The phase diagram shows that a eutectic mixture is formed with a weight fraction of D₂O of 0.57 and a melting point of 264 K. A change in the curvature of the polymer liquidus curve occurs when the ratio of D₂O to EO repeat unit is 1.2. For higher water contents the liquidus curves can be fitted by the Flory–Huggins theory. Enthalpies of fusion have been used to calculate the enthalpy of mixing of the two components at 264 K. A maximum exothermicity is found for a D₂O/EO ratio of 1.3 ± 0.1. Quenching of mixtures with either high or low water contents in liquid nitrogen produces glassy polymer which undergoes devitrification and cold crystallization on heating. Plots of the enthalpies of cold crystallization against weight fraction of D₂O indicate that the maximum amount of glass is formed at a D₂O/EO ratio of 0.9 ± 0.3. It is concluded that the average hydration number of the EO group is approximately one.