Liquid polyethylene glycol (PEG), in combination with carbon dioxide (CO2) and common organic solvents, enables the Coupling of a homogeneous reaction with a heterogeneous separation. This is important for the application of homogenous catalysts, which offer superior reactivity but are difficult to separate and recycle. CO2 can act as a miscibility switch to shift the system from homogeneous at atmospheric conditions to heterogeneous under CO2 pressure. This allows for extraction of the products into the organic solvent phase and immobilization of the homogeneous catalyst in the PEG phase. This work examines the phase behavior of PEG and carbon dioxide with 1,4-dioxane and acetonitrile at 25 and 40 C and pressures ranging from 5 to 8 MPa. The experimental data are compared to theoretical calculations using the Sanchez-Lacombe equation of state. (c) 2008 Elsevier B.V. All rights reserved.