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 CO 2 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.

Influence of tert-amine groups on the solubility of polymers in CO2

“…The calculated interaction energy is À19 kJ/mol. To put this binding energy in context, we note that interaction of CO 2 with the carbonyl oxygen of isopropyl acetate (IPA) is À15.9 kJ/mol [16] and that IPA is a surrogate for poly(vinyl acetate), a polymer that has been identified as having the highest CO 2 -solubility of any known oxygenated hydrocarbon polymer (a polymer containing only carbon, oxygen, and hydrogen) [16].…”

“…Spectroscopic [7][8][9][10] and theoretical [11][12][13] investigations have provided insight related to the favorable thermodynamic interactions between dense CO 2 and the fluorinated and siloxane-based polymers. There is a general consensus that the ability of these polymers to dissolve in CO 2 is related to their low glass transition temperature, low cohesive energy density [14,15], and Lewis acid-Lewis base interactions between the polymers and CO 2 [3,16].…”

Modeling Solvation in Supercritical CO2

“…[150] Co-polymers of tetrafluoroethylene and vinyl acetate exhibit enhanced bindingw ith CO 2 only if the solvent molecule can access both the fluorinated (Lewis base) and the hydrogenated( Lewis acid) parts of the backbone. [151] The first computational work simulating the self-assembly of af luorinated surfactant wasp erformed by Cumming andc ollaborators. [152] Further MD simulation studies focused on the formationo fr eversem icelles, on the structure-property relationship for different surfactant molecules, [153] and on the CO 2 -philic behavior of the surfactant tails.…”

Measurement of solubilities for rhodium complexes and phosphine ligands in supercritical carbon dioxide

“…The enhancements of catalyst solubilities in SCCO 2 are needed for the increase of the reaction rates. Some studies have reported that the solubilities in SCCO 2 are enhanced by the fluorinations of the solutes for the metal complexes [4][5][6], ligands [7], polymers [8], pharmaceuticals [9] and surfactants [10].…”