Vinylidene fluoride polymerization by metal-free selective activation of hydrogen peroxide: microstructure determination and mechanistic study

Abstract

Hydrogen peroxide-initiated radical polymerization of vinylidene fluoride (VDF) at 130 °C in dimethyl carbonate is presented. Various reaction parameters such as the nature of the solvent, the nature and the amount of the additive, and the reaction temperature were optimized. Hydrogen peroxide was activated with azobisisobutyronitrile (AIBN), which was not able to initiate the radical polymerization of VDF but afforded hydroxyl radicals via selective homolytic cleavage of the O–O bond of H₂O₂. The reactivity of hydroxyl radicals with the different components of the medium was evaluated. Two pathways were highlighted: the first one is the radical polymerization of VDF initiated by the OH˙ radical, while the second one is hydrogen abstraction from the solvent that afforded carbon-centered carbonate radicals. The latter was also able to initiate the radical polymerization of VDF. The microstructure of the resulting PVDFs was determined by NMR spectroscopy and MALDI-TOF spectrometry. Seven different chain-ends were identified and could be well revealed from synthesized models: 60% were functional, e.g., carbonates, alcohols, carboxylic acids and fluorinated olefins, whereas 40% were CF₂H and CF₂CH₃ fluoroalkyls as the products of hydrogen transfer termination reactions. Finally, based on the collected experimental data, a mechanistic pathway of the polymerization was proposed in order to explain the formation of such different functional and non-functional end-groups. In addition, the selectivity of the different radical additions onto VDF was studied and is discussed.