Radical Homopolymerization of Vinylidene Fluoride Initiated by tert-Butyl Peroxypivalate. Investigation of the Microstructure by 19F and 1H NMR Spectroscopies and Mechanisms

The radical polymerization in solution of vinylidene fluoride (VDF) initiated by different peroxides (tert-butyl peroxide and tert-butyl peroxypivalate) and by azo-tert-butane is presented. Various reaction temperatures and times and solvents were chosen to monitor the polymerization in terms of initiating radical generated from these initiators and transferring agents. Homopolymers thus obtained were characterized by 19F and 1H NMR spectroscopies. Different VDF telomers were synthesized (e.g., C4F9(CH2CF2)3H, C6F13CH2CF2CH2CH3, and CH3CF2(CH2CH2)2I) as models to explain the microstructure of these PVDFs. They enable one to identify without any ambiguity most different signals observed in 1H and 19F NMR spectra of PVDFs. From those assignments, an overall reactional mechanism was proposed that allows one to explain each step of polymerization of VDF. In particular, an interpretation of the polymer microstructures and of end groups arising from the radical initiator and from eventual transfers is suggested.