Comparison of the solubility of PVF and PVDF in supercritical CH2F2 and CO2 and in CO2 with acetone, dimethyl ether, and ethanol

Abstract

Cloud-point data are reported at temperatures to 245 degrees C and pressures to 2700 bar for poly(vinyl fluoride) (PVF) and poly(vinylidene fluoride) (PVDF) in CO2, CH2F2, dimethyl ether (DME), acetone, and ethanol and in mixtures of CO2 with acetone, DME, and ethanol. PVF does not dissolve in CO2 even at 245 degrees C and 2700 bar, but, PVF does dissolve in CH2F2 at 180 degrees C and pressures in excess of 1500 bar. To dissolve PVF in DME, pressures in excess of 550 bar and temperatures in excess of 130 degrees C are needed although it only takes similar to 100 bar to maintain a single phase to temperatures of similar to 220 degrees C with ethanol and acetone. Compared to the conditions needed to dissolve PVF, it takes hundreds of bar less pressure to dissolve PVDF in CO2, CH2F2, and DME and similar to 60 bar less pressure to dissolveit in acetone, but it does take similar to 60 bar more pressure to dissolve it in ethanol. With CO2, ethanol is a better cosolvent than acetone for both fluoropolymers at high temperatures and at low ethanol concentrations. However, when the temperature is decreased or the ethanol concentration is increased, it acts as an antisolvent probably due to ethanol self-association, Compared to ethanol and acetone, DME is not as good a cosolvent more than likely as a result of its lower density and smaller dipole moment. For all three cosolvents, their impact on the reduction of the cloud-point pressure diminishes with increasing cosolvent concentration. It is also evident that CO2 is an effective antisolvent since small amounts of it added to the polymer-cosolvent mixtures greatly increase the pressures needed to obtain a single phase.