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)(z)I containing one or several tetrafluoroethylene (TFE), vinylidene fluoride (or 1,1-difluoroethylene, VDF), hexafluoropropene (HFP) or triflu oroethylene (TrFE) base units were synthesized by thermal step-wise cotelom erization of these fluoroolefins with perfluoroalkyl iodides. H-1 and F-19 NMR allowed one to characterize these cotelomers and to assess the defects of chaining arid the molecular weights. While the monoadduct produced from VDF exclusively exhibits RFCH2CF2I structure, that prepared from TrFE was c omposed of RFCFHCF2I and RFCF2CFHI isomers, the ratio of which is directed from the electrophilicity of R-F* radical. The reactivity of the C-I bond i n R-F-Q-CXY-I depends on the nature of the Q spacer and on the reactivity o f the fluorinated monomer (e.g., thermal initiations of VDF, TrFE and HFP w ere efficient from 180, 195 and 210 degrees 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 t he more nucleophilic (i.e., the less electrophilic) side of the olefin. Eth ylenation 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, T-g and melting temperatures, T-m) were assessed. They were l inked to the number of consecutive CF2 groups (for the crystalline zones) a nd bulky side groups which induced amorphous regions. (C) 2000 Elsevier Sci ence S.A. All rights reserved.