Solubility of CF₂-modified polybutadiene and polyisoprene in supercritical carbon dioxide

The cloud-point behavior of fluorinated polyisoprenes (FPI) and fluorinated polybutadienes (FPBD) in supercritical fluid (SCF) CO₂ are reported at temperatures from 60 to 170°C and pressures from 1000 to 3000 bar. These fluorinated polymers were prepared by the addition of difluorocarbene (CF₂) to the parent polydienes yielding a gem-difluorocyclopropane repeating unit, a segment containing both fluorine and a significant dipole moment. Neither the unmodified polyisoprene starting material nor the hydrogenated variant dissolves in CO₂ up to temperatures of 155°C and pressures of 2600 bar. Both FPI and FPBD dissolve in CO₂, but pressures in excess of 1000 bar are needed to obtain a single phase. The PFI and PFBD cloud-point curves exhibit temperature minima at approximately 60 and 80°C, respectively, likely due to an increase in CO₂-CO₂ and polymer-polymer interactions relative to polymer-CO₂ interactions. As the amount of CF₂ incorporation in FPI samples decreases, the cloud-point curves shift to higher pressures and to higher temperatures. In a series of FPBD samples, an increase in cloud-point pressure with increase in molecular weight is initially large for molecular weights less than 10⁵ and then becomes much less at higher molecular weights, as also observed for other polymer-SFC solvent mixtures. This methodology for incorporation of fluorine into macromolecules leads to significant enhancement of solubility in CO₂.