Impact of "free" monomer concentration on the phase behavior of supercritical carbon dioxide-polymer mixtures

Cloud-point data demonstrate that ethyl and butyl methacrylate (EMA and BMA) cosolvents reduce the conditions needed to solubilize poly(ethyl methacrylate) (PEMA) and;poly(butyl methacrylate) (PBMA) in CO2. Although PEMA does not dissolve in CO2 to temperatures of 250 degreesC and pressures of 2500 bar, PEMA dissolves in CO2 at temperatures below 150 degreesC and pressures below 1000 bar if similar to 10 wt % EMA cosolvent is used. The PEMA-CO2-EMA and PBMA-CO2-BMA. cloud-point curves are shifted below 40 degreesC and 600 bar with similar to 30 wt % methacrylate (MA) cosolvent; however, the impact of the cosolvent diminishes as its concentration increases. BMA and EMA provide favorable polar interactions with the MA groups in the polymer, they increase the solvent density which magnifies the strength of polymer-cosolvent interactions, and they reduce the free-volume difference between the polymer and the solvent. The phase behavior of the binary CO2-EMA and CO2-BMA systems is also reported.