In this study, the high-pressure phase behavior of poly[p-decyl(oxy, thio, sulfonyl)methyl styrene] and poly[p-perfluorooctyl-ethylene(oxy, thio, sulfonyl)methyl styrene] in supercritical solvents comprised of carbon dioxide (CO 2 ) and dimethyl ether (DME) were examined. When the poly[p-perfluorooctyl-ethylene(oxy, thio, sulfonyl)methyl styrene]+CO 2 systems were evaluated, cloud-point pressures were obtained at temperatures ranging from 60 to 180°C and pressures of up to 1300bar. In addition, the poly[p-perfluorooctyl-ethylene(oxy, thio, sulfonyl)methyl styrene]+DME mixtures dissolved at temperatures under 180°C and pressures under 200bar, but the poly[p-decyl(oxy, thio, sulfonyl)methyl styrene]+CO 2 mixtures did not dissolve, even at 230°C and 2800bar. However, the poly[p-decyl(oxy, thio, sulfonyl)methyl styrene]+DME mixtures readily dissolved at temperatures and pressures under 180°C and 200bar, respectively. Furthermore, the cloud-point curves for the poly(p-decyl sulfonyl methyl styrene)+DME mixtures with 15.6, 44.3 and 56.4wt% CO 2 changed the P–T curve from a lower critical solution temperature (LCST) type to an upper critical solution temperature (UCST) type at increased CO 2 concentrations.