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

Abstract

Thermodynamic phase equilibrium data relevant to the copolymerization of carbon dioxide (CO 2 ) 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 CO 2 . Therefore, the solubility of poly(cylcohexene carbonate) (PCHC) in CO 2 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 CO 2, 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.