Phase behavior and density of polysulfone in binary fluid mixtures of tetrahydrofuran and carbon dioxide under high pressure: Miscibility windows

摘要

Mixtures of tetrahydrofuran (THF) and carbon dioxide (CO2) were identified as new solvent systems for polysulfone. The miscibility and density of polysulfone in binary fluid mixtures of THF and CO2 were investigated from 300 to 425 K at pressures up to 70 MPa. The influence of the CO2 and polysulfone concentrations was studied, with the concentrations of the other two components kept constant. At a 4.5 wt % polymer concentration, the demixing pressures in a 10 Wt % CO2 and 90 wt % THF mixture increased with temperature (310-425 K) from 15 to 40 MPa. With increasing CO2 concentration (from ca. 10 to 14 wt %), a significant increase (from 15 to 70 MPa at 310 K) was observed in the demixing pressures. Furthermore, with an increasing amount of CO2, the nature of the phase boundary shifted from lower critical solution temperature behavior to upper critical solution temperature behavior. The influence of the polymer concentration was studied in the 0-5 wt % range at two CO, levels, with solvent compositions of 10 wt % CO2 and 90 wt % THF and 13 wt % CO2 and 87 wt % THF. The system with a higher level of CO2 (13 wt %) showed highly unusual phase behavior: on pressure- composition and temperature-composition diagrams, the system displayed two distinct regions of miscibility. In the system with 10 wt % CO2, the distinct regions of miscibility that were observed in the system with 13 wt % CO2 partially overlapped and led to a W-shape phase boundary. The densities of the polymer solutions were measured from the one-phase region through the demixing point into the two-phase region at a constant temperature. No significant change in density was found around the phase boundary; this indicated that the coexisting phases had similar densities, as is often the case with liquid-liquid phase separation in polymer solutions under high pressure. (C) 2002 Wiley Periodicals, Inc. [References: 11]