In situ Fourier transform IR and UV-vis spectroscopy have been used for partitioning of solutes between supercritical (sc) CO2 and polymer phases. Partitioning of deuterated water and ate-dyes between poly(methyl methacrylate) and scCO(2) have been measured. Despite the low solubilities of polar ate-dyes in scCO(2) the partition coefficient of these dyes is ca. 10(4). In addition, the degree of partitioning of cosolvents methanol and acetone from scCO(2) into cross-linked poly (dimethylsiloxane) as well as the pressure dependence of the partition coefficient have been determined. Specific intermolecular interactions have been identified and related to the cosolvent partitioning between scCO(2) and polymer phases.