Experimental cloud-point data of binary and ternary mixtures for poly(isodecyl methacrylate) [P(IDMA)] in supercritical carbon dioxide, dimethyl ether (DME), propane, propylene, butane and 1-butene have been studied experimentally using a high pressure variable volume view cell. These systems show the phase behavior at temperature of 308 K to 473 K and pressure up to 255MPa. The cloud-point curves for the P(IDMA)+CO2+isodecyl methacrylate (IDMA) are measured in changes of the pressure-temperature (P-T) slope, and with cosolvent concentrations of 0-60.1 wt%. Also, experimental data of phase behaviors for IDMA in supercritical carbon dioxide is obtained at temperature range of 313.2-393.2 K and pressure range of 5.8-22.03 MPa. The experimental results were modeled with the Peng-Robinson equation of state. The location of the P(IDMA)+CO2 cloud-point curve shifts to lower temperatures and pressures when DME is added to P(IDMA)+CO2 solution. The P(IDMA)+C4 hydrocarbons cloud-point curves are ca. 16.0 MPa lower pressures than the P(IDMA)+C3 hydrocarbons curves at constant temperature.