The initiation of the radical polymerization of main chain fluorinated monomers such as vinylidene fluoride (VDF) typically requires very reactive primary alkyl radicals and high temperatures. We have already demonstrated that the visible light photolysis of Mn2(CO)10 (i.e., (CO)5Mn-Mn(CO)5) produces very reactive Mn(CO)5● radicals that can abstract halides and consequently initiate the radical polymerization of VDF from a variety of alkyl, semi- and perfluoroalkyl R-X halides even at room temperature. However, the Mn(CO)5● radicals do not add to VDF to initiate the polymerization under such conditions. Recently, we have also shown that by contrast, the photolysis of similar group 14 dimers R’3Q-QR’3 (R’ = alkyl, aryl, Q = Sn, Ge, Pb) generates a mixture of R● and QR3● radicals which do add to VDF and other monomers, and act as universal initiators for free radical polymerizations (FRPs) even in the absence of R-X. As group 14 radicals QR’3● radicals (e.g. Bu3Sn●) are classic radical halide abstractors, we decided to similarly evaluate them in conjunction with alkyl halides. We are presenting herein the evaluation of a series of regular and perfluorinated chlorine (CH3-(CH2)5-Cl, -(CH2-CHCl-)n-, Cl-CH2-(-CH-O-CH2-), Cl-CH2CH2-Cl, Cl-CH2-Cl, CCl4, CCl3-(CF2-CFCl)n-Cl, Cl-(CF2)8-Cl) and bromine (CH3-(CH2)5-Br, Br-CH2-Br, CCl3Br, Br-(CF2)6-Br) derivatives as chain transfer agents in the radical polymerization of VDF mediated by the photolysis of Me3Sn-SnMe3 and Bu3Sn-SnBu3. An in-depth investigation by a combination of 1H and 19F NMR reveals that polymerization is driven by a competition between initiation with R’6Sn2 (R’●, R’3Sn●,) solvent (CH3-O-CO-CH2● and CH3-CO-CH2●), and R-X derived R● radicals, and controlled by the bond dissociation energy (BDE) of R-X, i.e. by its chain transfer constant. As such, tin and solvent-derived initiation fragments are observed for CH3-(CH2)5-Cl, -(CH2-CHCl-)n-, Cl-CH2-(-CH-O-CH2-), Cl-CH2CH2-Cl, Cl-CH2-Cl, CCl3-(CF2-CFCl)n-Cl, and respectively, CH3-(CH2)5-Br and Br-CH2-Br. By contrast, polymers obtained with the better chain transferring R-X derivatives with lower C-X BDE such as CCl4, Cl-(CF2)8-Cl, and respectively CCl3Br and Br-(CF2)6-Br display not only R initiator fragments, but also Cl and Br chain ends, i.e., R-CH2-CF2-PVDF-CH2-CF2-X. However, since this is just a regular and not a degenerative chain transfer process, the polymerization remains a typical FRP.

Free radical polymerization of vinylidene fluoride initiated by the photolysis of R6Sn2 (R = Me, Bu) in the presence of alkyl and perfluoroalkyl chloride and bromide chain transfer agents

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