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

The equation of state of the poly(propylene glycol) (PPG) + water system ha s been measured using a vibrating tube densimeter in the intervals 0.1 less than or equal to P/MPa less than or equal to 40.0 and 298.15 less than or equal to T/K less than or equal to 328.15, and over the whole composition r ange. The P-rho-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 D elta G(E) and Delta H-E. The corresponding states equation proposed by Huan g and O'Connell (Fluid Phase Equilibr., 1987, 37, 75) fails when applied to the present systems. Although the master curve proposed by Sanchez et al. (Macromolecules, 1993, 26, 4234) does not describe the P-p-T surface of PPG + water with the same degree of precision as that for the PPG + n-hexane o r of PPG + ethanol, it still, can be useful for estimating high-pressure da ta from low-pressure isothermal compressibility data.