PHASES BEHAVIOR OF POLYMER SUPERCRITICAL CHLORODIFLUOROMETHANE SOLUTIONS

The phase behavior of solutions of poly(methyl methacrylate) and polycaprolactone (PCL) in supercritical chlorodifluoromethane (CDFM) has been studied experimentally using a high-pressure variable-volume view cell; LCST phase behavior was observed. The P-x and T-x demixing curves were generally flat up to the maximum concentration studied of 19 wt % polymer. The Sanchez-Lacombe lattice fluid (LF) model was fit to the experimental data as well as to previously published data for polyethylene (PE)-propane and polyethylene-n-pentane mixtures. The LF model predicted LCST phase behavior in all cases. Without using adjustable mixing rule parameters, the LF model significantly overpredicted the demixing pressures and the slope of the demixing curves. The Panayiotou-Sanchez hydrogen bond model without LF parameters provided a somewhat improved description of the magnitude of the demixing pressures for the CDFM solutions but could not describe the experimental maximum pressure. Over a temperature range of 70-140-degrees-C, the experimental maximum pressure for the polymer-CDFM isotherms were fit using a single set of LF mixing rule parameters for each solution. Correct scaling of molecular weight was found for the PCL-CDFM and the PE-n-alkane solutions.