The influence of compressed carbon dioxide sorption on the phase behavior of polymer blends and diblock copolymers exhibiting lower critical solution temperatures (LCSTs) and lower disorder-to-order transitions (LDOTs), respectively, was studied using in situ high-pressure small-angle neutron scattering. Homogeneous blends of poly(deuterated styrene) and poly(vinyl methyl ether) phase separate at temperatures more than 115 degrees C below the ambient pressure LCST upon sorption of less than 3.3 wt % CO2. The LDOTs in symmetric poly(deuterated styrene)-block-poly(n-butyl methacrylate) copolymers having total molecular weights of 78 000 and 32 000 g/mol are depressed by as much as 250 degrees C upon exposure to supercritical CO2 at modest fluid-phase densities.