High-pressure phase behavior was measured for the CO2-cyclohexyl acrylate and CO2-cyclohexyl methacrylate system at 40, 60, 80, 100, and 120degreesC and pressure up to 206 bar. This system exhibits type I phase behavior with a continuous mixture-critical curve. The experimental results for the CO2-cyclohexyl acrylate and CO2-cyclohexyl methacrylate system were modeled using the Peng-Robinson equation of state. Experimental cloud-point data, at a temperature of 250degreesC and pressure of 2800 bar, were presented for ternary mixtures of poly(cyclohexyl acrylate)-CO2-cyclohexyl acrylate and poly(cyclohexyl methacrylate)-CO2-cyclohexyl methacrylate systems. Cloud-point pressures of poly(cyclohexyl acrylate)-CO2-cyclohexyl acrylate system were measured in the temperature range of 40 to 180degreesC and at pressures as high as 2200 bar with cyclohexyl acrylate concentrations of 22.5, 27.4, 33.2, and 39.2 wt %. Results showed that adding 45.6 wt % cyclohexyl acrylate to the poly(cyclohexyl acrylate)-CO2 mixture significantly changes the phase behavior. This system changed the pressure-temperature slope of the phase behavior curves from the upper critical solution temperature (UCST) region to the lower critical solution temperature (LCST) region with increasing cyclohexyl acrylate concentration. Poly(cyclohexyl acrylate) did not dissolve in pure CO2 at a temperature of 250degreesC and pressure of 2800 bar. Also, the ternary poly(cyclohexyl methacrylate)-CO2-cyclohexyl methacrylate system was measured below 187degreesC and 2230 bar, and with cosolvent of 27.4-46.7 wt %. Poly(cyclohexyl methacrylate) did not dissolve in pure CO, at 240degreesC and 2500 bar. Also, when 53.5 wt % cyclohexyl methacrylate was added to the poly(cyclohexyl methacrylate)-CO2 solution, the cloud-point curve showed the typical appearance of the LCST boundary. (C) 2004 Wiley Periodicals, Inc.