Synthesis and Solubility of Linear Poly(tetrafluoroethylene-co-vinyl acetate) in Dense CO2: Experimental and Molecular Modeling Results

Abstract

Supercritical carbon dioxide was used as a reaction medium to synthesize statistically random (i.e., no specific correlation between the location of the monomers on the polymer) copolymers of tetrafluoroethylene (TFE) and vinyl acetate (VAc) with similar molar mass and 11.6−63.3 mol % TFE content. The solubility of the copolymers at 25 °C in CO2 reduced after reaching a maximum value at a TFE molar concentration of 19.3 mol %. The 46.7 mol % TFE copolymer only dissolved in CO2 at elevated temperatures, whereas the 63.3 mol % TFE copolymer did not dissolve in CO2 even at temperatures in excess of 144 °C and pressures of 210 MPa. The molecular modeling results show that the interaction of CO2 with acetate side group was not affected by presence of fluorine in the polymer backbone; therefore, the enhanced solubility of the semifluorinated copolymers is attributable to the enhanced binding between CO2 and the semifluorinated backbone of the copolymer when the CO2 molecule can access both the fluorinated (Lewis base) and hydrogenated (Lewis acid) parts of the backbone simultaneously.