Novel Method to Assess the Molecular Weights of Fluoropolymers by Radical Copolymerization of Vinylidene Fluoride with Various Fluorinated Comonomers Initiated by a Persistent Radical

Batch radical homopolymerization of vinylidene fluoride (VDF) and its copolymerizations with seven fluorinated comonomers such as H2C═CRACF3 (where RA stands for H, F, CO2R (R = H or tBu) or F2C═CFRB (RB: H, CF3, OCF3) initiated by •CF3 radical generated from a perfluoro-3-ethyl-2,4-dimethyl-3-pentyl persistent radical (PPFR) are presented. That highly perfluorinated branched radical itself was unable to directly initiate the copolymerization in contrast to the generated trifluoromethyl radical that was successful. The microstructures of the resulting PVDFs, poly(VDF-co-H2C═CRACF3) or poly(VDF-co-F2C═CFRB) (co)polymers were assessed by 19F and 1H NMR spectroscopy. 19F NMR spectra displayed a quintet centered at −61 ppm assigned to a CF3 end-group which enabled one to determine both the molecular weights of the resulting (co)polymers and the amounts (numbers and molar percentages) of these above comonomers. In all cases, the regioselective radical addition of •CF3 onto the methylene site of VDF was noted a...