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Comparison of the Solubility of PVF and PVDF in Supercritical CH 2 F 2 and CO 2 and in CO 2 with Acetone, Dimethyl Ether, and Ethanol

1999; American Chemical Society; Volume: 103; Issue: 14 Linguagem: Inglês

10.1021/jp9844462

1520-6106

Michele Lora, Jong Sung Lim, Mark A. McHugh,

Carbon dioxide utilization in catalysis

Cloud-point data are reported at temperatures to 245 °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 °C and 2700 bar, but, PVF does dissolve in CH2F2 at 180 °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 °C are needed although it only takes ∼100 bar to maintain a single phase to temperatures of ∼220 °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 ∼60 bar less pressure to dissolve it in acetone, but it does take ∼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.