High-Pressure Phase Behavior of the System PCHC-CHO-CO2 for the Development of a Solvent-Free Alternative toward Polycarbonate Production

Thermodynamic phase equilibrium data relevant to the copolymerization of carbon dioxide (CO2) and cyclohexene oxide (CHO) are reported in this paper. In this system, the need for additional solvents can be prevented by using an excess of the comonomer CO2. Therefore, the solubility of poly(cylcohexene carbonate) (PCHC) in CO2 and the effects of molecular weight and CHO concentration have been experimentally determined using a high-pressure view cell. Since extremely high pressures are required to dissolve PCHC in CO2, only low-molecular-weight polymer is soluble within the experimental pressure range. Addition of CHO results in a significant decrease of the cloud-point pressures and a change of the slope of the cloud-point curve in PT-space. The perturbed-chain SAFT equation of state has been successfully used for the correlation and the prediction of the phase behavior in this range. At high temperatures the PC-SAFT model allows for a quantitative description of the phase behavior, whereas at lower temperatures PC-SAFT tends to overestimate the cloud-point pressures.