Experimental cloud-point data to 210 ℃ and 2,200 bar are presented for binary and ternary mixtures of poly(methyl acrylate)-CO₂-methy acrylate and poly(ethyl acrylate)-CO₂, propylene, and 1-butene-ethyl acrylate systems. The accuracy of the experimental apparatus was tested by comparing the measured pressure-temperature phase behavior data of the poly(ethyl acrylate)-CO₂ system obtained in this study with those of Rindfleisch et al. [1995]. The phase behaviors for the system poly(methyl acrylate)-CO₂-methyl acrylate were measured in changes of pressure-temperature slope, and with cosolvent concentrations of 0, 5.0, 13.7, 25.3, and 43.3 wt%, respectively. With 48.3 wt% methyl acrylate to the poly(methyl acrylate)-CO₂ solution significantly changes, the phase behavior curve takes on the appearance of a typical lower critical solution temperature (LCST) boundary. The impact of ethyl acrylate on the cloudpoint for the poly(ethyl acrylate)-CO₂ system shows the change of slope of the phase behavior curves from negative to positive with ethyl acrylate concentration of 0, 8.2, and 25.0 wt%. The cloud-point behavior for the poly(ethyl acrylate)-CO₂-39.5 wt% ethyl acrylate system shows an LCST curve. The solubility curve to ~150 ℃ and 1,650 bar for poly(ethyl acrylate)-propylene-ethyl acrylate system shows the change of pressure-temperature diagram and with ethyl acrylate concentration of 0, 7.2 and 21.0 wt%. Also, when 41.1 wt% ethyl acrylate was added to the poly(ethyl acrylate)-propylene solution, the phase behavior curve showed the LCST region. The high pressure phase behavior of poly(ethyl acrylate)-1-butene-0, 3.1, 8.1, 18.5 and 30.7 wt% ethyl acrylate system presented the change of pressuretemperature curve from the UCST region to U-LCST region as the ethyl acrylate concentration increased.