The solubility of gases in aqueous solutions of poly(propylene glycol)

Measurements have been made to determine the solubilities of four gases, argon, methane, ethane, and propane, at 25 degreesC in binary solutions of water and poly(propylene glycol)s (PPGs) having average molecular weights of 400 and 725, respectively. The lower critical solution temperature (LCST) for PPG having an average molecular weight of 400 is approximate to 50 degrees C (P: Firman and M. Kahlweit, Colloid Polym. Sci. 264, 936, 1986; technical data provided by BASF Corp.), thus allowing gas solubilities to be measured over a complete range of PPG concentrations at 25 degreesC. The LCST for PPG having an average molecular weight of 725 is approximate to 15 degreesC and the phase diagram is such that homogeneous solutions suitable for gas solubility measurements at 25 degreesC are effectively limited to concentrations below 10 wt% and above 85 wt% PPG. Dissolved PPG acts to increase the solubility of each gas relative to its solubility in water. The degree of enhancement in gas solubility exhibits a distinctly nonlinear dependence on PPG concentration much like that found previously with poly(ethylene glycol) (A. D. King, Jr., J. Colloid Interface Sci. 144, 579, 1991). Gas solubilities measured with solutions containing PPG having an average molecular weight of 725 differ only slightly from those obtained at similar concentrations with PPG having an average molecular weight of 400, indicating that molecular weight of the polymer plays a minimal role in determining gas solubilities for these systems. Standard free energies of solution for these gases in aqueous PPG solutions are found to exhibit many similarities to those measured for these same gases in other aqueous solutions of nonelectrolytes. (C) 2001 Academic Press.