Solubilization of gases by poly(ethylene oxide)-poly(propylene oxide) triblock copolymers

Measurements have been made to determine the solubilities of threehydrocarbon gases, methane, ethane, and propane, in aqueous solutions of four different water-soluble triblock copolymers of the Pluronic class: Pluronic P103, P104, P105, and F108. The solubilities of each gas, measured at 25 C, follow Henry's Law. At concentrations above the critical micelle concentration, the solubilities increase linearly with polymer concentration as would be expected if micellar solubilization occurs. The micellar gas solubilities derived from these data increase in the order CH4 < C2H6 < C3H8 for each polymer, as would be expected for gas absorption in a nonpolar microenvironment. The micellar solubilities of each gas are found to increase linearly with poly(propylene oxide) content of the individual polymers, indicating that the polymerized ethylene oxide chains do not contribute to gas solubilization. The sorptive capacity of the hydrophobic core region of these Pluronic micelles is found to be less than that determined earlier for for these same gases in pure low-molecular-weight poly(propylene glycol) and closely approximates gas solubilities obtained with concentrated (90 wt%) solutions of poly(propylene glycol) and water. This suggests that the poly(propylene oxide) residing in the core regions of Pluronic-type micelles exists in a partially hydrated rather than anhydrous condition. (C) 2001 Academic Press.