This study's purpose is to probe the binary and ternary systems phase behavior including vinyl toluene and poly(vinyl toluene) + co-solvents in supercritical solvent i.e. supercritical CO2 respectively. The vapor + liquid phase behavior of a binary supercritical CO2 + vinyl toluene solution was investigated at five different temperatures from 313.2 K to 393.2 K, up to 20.55 MPa of pressure, and vinyl toluene liquid phase mole fractions ranging from 0.070 to 0.67. Experimental data were compared to computed values using the Peng-Robinson, and Patel-Teja cubic equations of state. At each temperature, the results demonstrated good agreement with experimental readings.The phase separation behavior of poly(vinyl toluene) [P(VT)] + monomers (vinyl toluene, dimethyl ether, toluene, xylene) solutions under supercritical CO2 was presented from 304.55 K to 434.75 K at a pressure range of 14.66–192.59 MPa with different monomer concentration ranges. P(VT) + monomers (vinyl toluene, xylene) + supercritical CO2 ternary mixture phase transition shows phase gradient region from upper critical solution temperature (UCST) to upper-lower critical solution temperature (U-LCST) region in (pressure vs temperature) diagram. Furthermore, P(VT) + monomers (dimethyl ether, toluene) + supercritical CO2 demonstrates UCST to LCST phase separation curves.