Controlled step-wise telomerization of vinylidene fluoride, hexafluoropropene and trifluoroethylene with iodofluorinated transfer agents

Highly fluorinated cotelomers having the structure F(TFE)w(VDF)x(HFP)y(TrFE)zI containing one or several tetrafluoroethylene (TFE), vinylidene fluoride (or 1,1-difluoroethylene, VDF), hexafluoropropene (HFP) or trifluoroethylene (TrFE) base units were synthesized by thermal step-wise cotelomerization of these fluoroolefins with perfluoroalkyl iodides. 1H and 19F NMR allowed one to characterize these cotelomers and to assess the defects of chaining and the molecular weights. While the monoadduct produced from VDF exclusively exhibits RFCH2CF2I structure, that prepared from TrFE was composed of RFCFHCF2I and RFCF2CFHI isomers, the ratio of which is directed from the electrophilicity of RF radical. The reactivity of the C–I bond in RF-Q-CXY-I depends on the nature of the Q spacer and on the reactivity of the fluorinated monomer (e.g., thermal initiations of VDF, TrFE and HFP were efficient from 180, 195 and 210°C, respectively). The mechanism of the addition of the radical generated from the iodinated transfer agent to the fluoroalkene is explained by means of its electrophilic attack to the more nucleophilic (i.e., the less electrophilic) side of the olefin. Ethylenation of these fluorocotelomers was successfully achieved from various initiations (thermal, redox or from peroxides) with best results from redox catalysis. Thermal properties of several fluorotelomers (glass transition temperatures, Tg and melting temperatures, Tm) were assessed. They were linked to the number of consecutive CF2 groups (for the crystalline zones) and bulky side groups which induced amorphous regions.