Phase behavior and volumetric properties of poly (epsilon caprolactone) (PCL) + acetone + CO2 mixtures were determined in a variable-volume view cell at 323, 348, 373, and 398 K and at pressures up to 50 MPa. Effect of temperature, pressure, polymer concentration (1 – 20 wt %), polymer molecular weight (14 K and 65 K) and carbon dioxide concentration (0 – 60 wt %) on the liquid-liquid phase boundary and the density were explored. Complete miscibility of mixtures with PCL concentrations up to 20 wt % could be achieved in fluid mixtures containing up to 50 wt % carbon dioxide at modest pressures (5 – 40 MPa). The solutions showed LCST-type phase behavior.

The mixture densities were in the range of 0.58 - 1.20 g/cm3. The L-L phase separation leads to no detectable change in the mixture densities, while the L-L-V phase separation shows itself with a sharp change in the mixture density. Densities of the polymer solutions were found to increase significantly with PCL concentration. A mixture density crossover was observed at around 25 MPa at carbon dioxide concentrations higher than 20 wt %. The densities of solutions with different polymer molecular weight samples were close to each other, however, the low molecular weight polymer solutions displayed slightly higher densities.

Analysis of the isothermal compressibility of the polymer solutions and comparison with the solvent properties show that the compressibilities of PCL solutions are lower than that of the corresponding acetone + carbon dioxide mixture at low temperatures. There appears to be a characteristic temperature around 373 K where the compressibilities become equal to each other independent of the pressure. The difference in the isobaric compressibility of the solution and solvent decreases with pressure and displays a plateau value at around 25 MPa.