Solubility of CF2-Modified Polybutadiene and Polyisoprene in Supercritical Carbon Dioxide

Abstract

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−SCF solvent mixtures. This methodology for incorporation of fluorine into macromolecules leads to significant enhancement of solubility in CO2.