Equation of state of aqueous polymer systems: poly(propylene glycol)+water

Abstract

The equation of state of the poly(propylene glycol) (PPG)+water system has been measured using a vibrating tube densimeter in the intervals 0.1⩽P/MPa⩽40.0 and 298.15⩽T/K⩽328.15, and over the whole composition range. The P–ρ–T data can be well described by a generalized Tait equation. The results show that the effect of pressure on the relative molar volume is smaller than for both the PPG+ethanol and PPG+n-hexane systems. The excess volume is highly negative, and similar to that previously reported for poly(ethylene glycol)+water. Increasing the pressure decreases both ΔG^E and ΔH^E. The corresponding states equation proposed by Huang and O'Connell (FluidPhaseEquilibr., 1987, 37, 75) fails when applied to the present systems. Although the master curve proposed by Sanchez etal. (Macromolecules, 1993, 26, 4234) does not describe the P–ρ–T surface of PPG+water with the same degree of precision as that for the PPG+n-hexane or of PPG+ethanol, it still can be useful for estimating high-pressure data from low-pressure isothermal compressibility data.