Synthesis of linear poly(tetrafluoroethylene-co-vinyl acetate) in carbon dioxide

Tetrafluoroethylene (TFE) and vinyl acetate (VAc) were copolymerized in carbon dioxide by a free radical mechanism to yield a series of poly(TFE-co-VAc)s with weight-average molar masses, relative to polystyrene, between 110 and 209 kg mol(-1). The copolymer composition was controlled by the monomer feed concentration to have between 40 and 71 mol % TFE. Hydrolysis of the copolymer's vinyl acetate groups to vinyl alcohol (VA) yielded terpolymers, poly(TFE-co-VAc-co-VA), thereby providing a reactive functional group for further modification. Previous syntheses of poly(TFE-co-VAc) in aqueous media resulted in a branched structure due to radical hydrogen abstraction from VAc followed by continued propagation during polymerization. Consequently, a 10-fold or greater decrease in molar mass was observed following hydrolysis. Interestingly, after synthesizing poly(TFE-co-VAc) in supercritical carbon dioxide, only a small decrease in molar mass was observed after hydrolysis. This suggests that, in carbon dioxide, abstraction is suppressed relative to polymer propagation, thereby yielding predominantly linear poly(TFE-co-VAc).