Pressure-composition isotherms were measured for the CO 2 /octadecyl acrylate system at 45.0, 80.0, and 100.0°C and at pressures up to 307 bar. This system exhibited type I phase behavior with a continuous mixturecritical curve. The solubility of octadecyl acrylate for the CO 2 /octadecyl acrylate system increased as the temperature increased at a constant pressure. The experimental results for the CO 2 /octadecyl acrylate system were modeled with the Peng-Robinson equation of state. A good fit of the data was obtained with the Peng-Robinson equation of state with one adjustable parameter for the CO 2 /octadecyl acrylate system. Experimental cloud-point data for the poly(octadecyl acrylate)/CO 2 /octadecyl acrylate system were measured from 36 to 193°C and at pressures up to 2100 bar, and the added octadecyl acrylate concentrations were 11.9, 25.9, 28.0, 35.0, and 40.0 wt %. Poly(octadecyl acrylate) dissolved in pure CO 2 up to 250°C and 2100 bar. Also, adding 45.0 wt % octadecyl acrylate to the poly(octadecyl acrylate)/CO 2 solution significantly changed the phase behavior. This system changed the pressure-temperature slope of the phasebehavior curves from an upper critical solution temperature (UCST) region to a lower critical solution temperature region as the octadecyl acrylate concentration increased. Cloud-point data to 150°C and 750 bar were examined for poly(octadecyl acrylate)/C 2 H 4 /octadecyl acrylate mixtures at octadecyl acrylate concentrations of 0.0, 15.0, and 45.0 wt %. The cloud-point curve of the poly(octadecyl acrylate)/ C 2 H 4 system was relatively flat at 730 bar between 41 and 150°C. The cloud-point curves of 15.0 and 45.0 wt % octadecyl acrylate exhibited positive slopes extending to 35°C and approximately 180 bar.

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