High-pressure cloud-point data are presented for poly(tetrafluoroethylene-co-19.3 mol % hexafluoropropylene) (FEP19) in CF4, C2F6, C3F8, C3F6, CClF3, CO2, and SF6 at 118-250 °C and pressures as high as 2700 bar. Cloud-point curves for a given solvent virtually superpose for FEP19 concentrations between 2 and 10 wt %. It is not possible to dissolve FEP19 in CO2 at temperatures less than 185 °C due to strong quadrupolar self-interactions relative to cross-interactions between FEP19 and CO2. The location of the cloud-point curves in pressure-temperature space are directly related to the product of the polarizability and molar density, FiRi, of the solvent as determined at the cloud-point pressure at a given temperature. The average of FiRi is 5.14 × 10 -24 mol (7% for the SCF solvents considered in this study calculated at 200 °C and it is 5.41 × 10 -24 mol (7% for all of the solvents except CF4 and CO2 at 170 °C. This simple correlation provides a means for estimating cloud-point pressures for nonpolar polymers with nonpolar solvents, or for polar solvents at very high temperatures where polar interactions are diminished. Using this correlation, it is not possible to predict when crystallization may occur or when polar interactions will dictate the phase behavior as observed for CO2 at temperatures below 185 °C. With one temperature-independent and one temperature-dependent mixture parameter the Sanchez-Lacombe equation of state (SLEOS) is capable of modeling the phase behavior of FEP19 in the solvents considered in this study except for CO2 which required two temperature-dependent parameters. It is not possible to even qualitatively model the cloud-point behavior if the two mixture parameters are set to zero. Hence, the utility of the SLEOS is limited since cloud-point data are needed to fix the values and the temperature dependence of the mixture parameters.

Cloud-point data to 270 °C and 2800 bar are presented for poly(vinylidene fluoride-co-22.0 mol % hexafluoropropylene) (Fluorel) in supercritical fluid (SCF) C3F6, CClF3, CHF3, and CO2. The impact of backbone architecture on intermolecular interactions and fluorocopolymer solubility is determined by comparing the phase behavior of Fluorel to that of poly(tetrafluoroethylene-co-19.3 mol % hexafluoropropylene) (FEP19) in the same SCF solvents. Good solvents for nonpolar FEP19 (SF6 and C3F8) did not dissolve polar Fluorel even at temperatures in excess of 260 °C. Although the small dipole moments of C3F6 and CClF3 interact favorably with the polar, vinylidene fluoride segments of Fluorel, the cloud-point curves in these two solvents exhibit a sharp rise in cloud-point pressures as the temperature is decreased. Apparently, dipolar interactions between vinylidene fluoride segments are much stronger than Fluorel−C3F6 or Fluorel−CClF3 cross-interactions as the temperature is lowered. In contrast, quadrupolar CO2 and dipolar CHF3 are good solvents for Fluorel due to favorable polar, vinylidene fluoride segment−SCF solvent cross-interactions. However, at or near room temperature, CO2 is a much better solvent for Fluorel than is CHF3, which is speculated to be a result of specific interactions between CO2 and the vinylidene fluoride segments.