Synthesis of fluorocarbon-vinyl acetate copolymers in supercritical carbon dioxide: Insight into bulk properties

Tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE), and vinylidene fluoride (VDF) were copolymerized with vinyl acetate (VAc) in supercritical fluid CO2 by a free radical mechanism and without the use of a surfactant, A series of copolymers were synthesized with yields as high as 83% for TFE-VAc, 91% for CTFE-VAc, and 70% for VDF-VAc copolymers. Their weight-average molar masses, relative to polystyrene, were between 120 and 290 kg mol(-1), and polydispersity was between 1.6 and 2.4. A range of compositions was prepared with the amount of fluorocarbon in the copolymer varying from 13 to 84 mol 17c, as determined by elemental analysis. Monomer reactivity ratios were estimated using the error-in-variable method to be r(CTFE) = 0.014 +/- 0.05, r(VAc) = 0.44 +/- 0.03; r(TFE) = -0.009 +/- 0.06, r(VAc) = 0.95 +/- 0.08; and r(VDF) = -0.4 +/- 0.04, r(VAC) = 1.67 +/- 0.6. Proton NMR was used to estimate copolymer composition, based on triad sequences. These data, together with the reactivity ratio data, indicate that the fluorocarbons cross-propagate with VAc and that VAc propagates randomly. All samples were characterized by DSC for T-g with P(CTFE-co-VAc) having a Tg between 42 and 53 degreesC, P(TFE-co-VAc) between 34 and 41 degreesC, and P(VDF-co-VAc) between 20 and 33 degreesC. Hydrolysis of vinyl acetate to vinyl alcohol (VA) in P(TFE-co-VAc) yielded terpolymers, P(TFE-co-VAc-co-VA), with >80% of VAc hydrolyzed to VA, thereby providing a reactive functional group for further modification. Interestingly, only a small decrease in molar mass was observed after the hydrolysis of vinyl acetate to vinyl alcohol, reflecting the loss of acetic acid and suggesting that these polymers are linear. The results presented herein are particularly interesting because no surfactant (or dispersion agent) was required for apparent solubility in CO2. The fluoropolymers prepared herein may find utility in coatings or paint applications.