Attempt to explain the changes in solvation of polystyrene in supercritical CO2/ethanol mixtures using infrared and Raman spectroscopy

The polystyrene//CO₂/ethanol system has been investigated in the supercritical domain using infrared absorption (FTIR) and Raman scattering spectroscopies. The pressure and temperature were fixed in the range 20–35 MPa at 423 K for CO₂/ethanol mixtures with proportion in weight from (70/30) to (58/42). These conditions are those used in our previous study concerning the fractionation of this macromolecule. A surprising finding reported before was that the CO₂/ethanol mixture made of two non-solvents of PS at ambient conditions is able to dissolve PS chains under high temperature and pressure. In the present article, this question will be addressed at a microscopic level from a discussion of the intermolecular interactions between the polymer and the medium and between the CO₂ and ethanol components provided by the analysis of the spectra.