J. Balague et al., Controlled step-wise telomerization of vinylidene fluoride, hexafluoropropene and trifluoroethylene with iodofluorinated transfer agents, J FLUORINE, 102(1-2), 2000, pp. 253-268
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.