Pressure-composition (P-x) isotherms were obtained for the carbon dioxide + 4-chlorostyrene (4-CS) system using static apparatus at five temperatures (313.2, 333.2, 353.2, 373.2 and 393.2 K) and pressure up to 23.74 MPa. The experimental results for the carbon dioxide + 4-CS system were modeled with the Peng-Robinson equation of state (PR EOS) using two adjustable parameters. The comparison between the experimental results and the calculated curves shows a good agreement at five temperatures. Three phases were not observed at any five temperatures in this system. The experiments were conducted to obtain cloud-point data of binary and ternary mixture for the poly(4-chlorostyrene) [P(4-CS), Mw = 87,000, Mn = 57,000, polydispersity = 1.53] + supercritical solvents (propane, propylene, butane and 1-butene)+ acetone, the P(4-CS)+ supercritical solvents [butane, 1-butene and dimethyl ether (DME)] + 4-CS and the P(4-CS)+ supercritical solvents (butane and 1-butene)+ ethanol, the P(4-CS)+ supercritical solvents (propylene, 1-butene and DME) and the P(4-CS) + carbon dioxide + DME systems. High pressure phase behavior experiment for the binary and ternary mixture of the P(4-CS) + supercritical solvents + cosolvent systems is measured within a temperatures range of 332.8-494.2 K and pressure up to ca. 260.0 MPa. The P(4-CS) + supercritical solvents (propane, propylene and 1-butene)+ acetone systems show the changes in the pressure-temperature (p-T) curve from upper critical solution temperature (UCST) region to lower critical solution temperature (LCST) region as acetone concentration increases. The phase behavior curves for the P(4-CS) + supercritical solvents (butane, 1-butene)+ 4-CS systems of three systems [the P(4-CS) + 4-CS mixture in supercritical solvents (butane, 1-butene and DME)] exhibit UCST region with negative slopes, but in the case of the P(4-CS) + DME + 4-CS system, cloud-point behavior shows LCST-type curve with a positive slope. The cloud-point behaviors for P(4-CS)+ supercritical solvents (butane and 1-butene)+ ethanol systems exhibit USCT-type curves with negative slopes. The P(4-CS) + carbon dioxide + x wt.% DME system shows cloud-point curves changing from UCST region to LCST region as DME concentration increases. (C) 2012 Elsevier B.V. All rights reserved.