Effect of the octadecyl acrylate concentration on the phase behavior of poly(octadecyl acrylate)/supercritical CO 2 and C 2 H 4 at high pressures

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 mixture‐critical 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 phase‐behavior 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. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 372–380, 2002