A Kinetic and Mechanistic Study of the Low-Temperature Fluorine-Initiated Copolymerization of Tetrafluoroethylene with Oxygen

Abstract

The fluorine-initiated reaction of tetrafluoroethylene with oxygen, in a liquid phase at low temperature, leads to almost quantitative yields of polymeric perfluoroethers made by CF2CF2O and CF2O units and containing variable amounts of peroxy bonds. This chain reaction is studied in a series of semibatch experiments, and the results are interpreted on the basis of a rather simplified reaction mechanism involving a sequence of elementary steps of different free-radical species. A most unexpected experimental finding is the positive action exerted by the oxygen pressure on the initiation rate; this effect is attributed to a competitive reaction of fluorine atoms with molecular oxygen to form FO 2 reactive species which are able to produce a substantial number of chain-initiating biradicals. The kinetic relationships deduced from the overall reaction model are proved to fairly describe, in a quantitative way, the correlation between the operating variables and the various polymer structure indexes. The values of the typical kinetic parameters of the process are estimated; they appear to be consistent with an emerging general picture of the reactivity characteristics of the different perfluorinated oxygenated radical species in the condensed state.

Peroxidic perfluoropolyether from tetrafluoroethylene oxidation: micro structural analysis by NMR spectroscopy and mechanistic considerations

“…The fluorine chemical shifts of the different -CF 2 -groups in the polymer of formula (1) are well known and previously reported [2,8]; they are summarized in Table 2 for comparison with the recent results obtained with higher frequency instruments.…”

“…The perfluoromethylene units originate from carbon-carbon scission reactions of the growing perfluoroalkoxy radicals RfOCF 2 CF 2 O , as reported in previous work [2,3]. Longer carbon units (C3 and C4), arising from TFE addition to the carbon radicals, are present only in trace amount as the reaction is usually performed with oxygen in excess.…”

“…Several polymers of formula (1) with variable amount of peroxidic units, [OO], have been synthesized according to well-known procedures [2,3]. In particular, some samples have been prepared using the photochemical technique (photosynthesis) and the others using the fluorine initiated oxypolymerization technique, as reported in Table 1 and in Section 4.…”

“…The high rate of oxygen addition to the carbon radicals, close to the diffusion limit, results in the stationary concentration of the carbon radicals being orders of magnitude lower than that of the oxy radicals. Therefore, the radical propagating species are almost exclusively the perfluoroalkylperoxy (RfOO ) and the perfluoroalkoxy (RfO ) radicals [1,2].…”

Perfluoropoly-ether/peroxide compounds: spectroscopic studies and quantum chemical calculations

“…The fluorine resonances of the peroxidic polymer obtained from TFE oxypolymerisation are well known [7,8]; and are reported to make easier the discussion (See also Fig. 1 for spectrum relative to sample 4).…”