Thermodynamics of Poly(dimethylsiloxane)/Poly(ethylmethylsiloxane) (PDMS/PEMS) Blends in the Presence of High-Pressure CO₂

Abstract

Processing polymer blends in the presence of high-pressure carbon dioxide (CO2) affords numerous advantages over organic solvents and is becoming a commercially viable and environmentally responsible alternative in the development of new multicomponent materials. A prerequisite to such processing is a fundamental understanding of how high-pressure CO2 influences the phase behavior of polymer blends. In this work, we use high-pressure spectrophotometry to measure the cloud point (Tcp) of poly(dimethylsiloxane)/poly(ethylmethylsiloxane) (PDMS/PEMS) blends as a function of CO2 pressure (P) in the vapor phase. Results obtained here at different blend compositions indicate that values of Tcp for this upper critical solution temperature (UCST) blend (i) generally increase with increasing pressure and (ii) collapse onto a master curve of ΔTcp(P) for pressures up to about 35 MPa. These data are analyzed by the Sanchez−Lacombe equation of state to ascertain the temperature dependence of an effective interaction parameter (χ) in terms of A + B/T, where A and B are both pressure-sensitive. We also compare our results with previously reported data to delineate the role of hydrostatic pressure on the phase behavior of these blends.