| Abstract
| - While ongoing efforts continue to explore the high-pressure phase equilibria of polymer blends, few studieshave attempted to address the impact of a supercritical (sc) fluid on such equilibria. In this work, we reporton the phase behavior of an upper critical solution temperature (UCST) polymer blend in the presence ofsupercritical carbon dioxide (scCO2), a nonselective plasticizing agent. Blends composed of low-molecular-weight polystyrene and polyisoprene have been examined as a function of temperature in scCO2 by visualinspection, small-angle neutron scattering, and spectrophotometry. In the presence of scCO2, the cloud pointtemperature is depressed by as much as 28 °C, depending on both blend composition and CO2 pressure.Complementary studies performed with nitrogen decouple the plasticization efficacy of CO2 from free-volumecompression due to hydrostatic pressure. Existence of a pressure yielding a maximum in CO2-induced cloudpoint depression is established. These results provide evidence for enhanced polymer miscibility as a resultof the plasticizing effectiveness and tunable solubility of scCO2.
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