Jean-Marc Sage

Telomerization of vinylidene fluoride with methanol. Elucidation of the reaction process and mechanism by a structural analysis of the telomers

Telomerization of vinylidene fluoride (VDF) with methanol was investigated to synthesize fluorinated telomers bearing a functional end-group. Improvements of the conversion of VDF were attempted by using different radical initiators and reaction processes. The solvent effect on the reaction yield was also studied. Radically initiated telomerizations led to VDF oligomers, whereas thermal and photochemical initiations seemed ineffective. Di-tert-butyl peroxide is the most effective radical initiator. All these experiments revealed the low chain transfer activity of methanol in the presence of VDF. For instance, an average cumulated degree of polymerization DP n cum of 4.6 was obtained from an initial methanol/VDF mole ratio of 5. A minute structural study of typical VDF-methanol telomers was performed by NMR spectroscopy, proving, on the one hand, the non-regioselectivity of the addition of hydroxymethyl radicals to VDF and, on the other hand, the competitive formation of non-functional telomers issued from direct chain initiations by the radical initiator (mainly methyl radicals when di-tert-butyl peroxide was used as the initiator). An overall mechanism of the VDF-methanol telomerization initiated with di-tert-butyl peroxide was thus deduced.