Low-temperature fluorination of fluoro-containing polymers: EPR studies of polyvinylidenefluoride and the copolymer of tetrafluoroethylene with ethylene

The direct fluorination of polyvinylidenefluoride (PVDF) and the copolymer of tetrafluoroethylene with ethylene (CTE) was studied at 35-300 K. The dependence of radical formation on temperature and reaction time was obtained by use of electron paramagnetic resonance (EPR) spectroscopy. Primary alkyl radicals formed as a result of the reaction of fluorine abstracting a hydrogen from the polymer were detected at 35 K. These radicals rapidly react with molecular oxygen producing long-lived (∼48 h at 300 K) peroxy radicals. The peroxy radicals when subjected to UV-irradiation (λ < 280 nm) give rise to other radicals that are not stable at T > 77 K. The concentration of the radicals produced during fluorination of PVDF at 77-200 K is one order of magnitude less than that formed from CTE under similar conditions. A mechanism based on the abstraction of the H and the energies of the C-H bonds is given. Density functional theory was used to predict the structures and EPR parameters for a number of fluorinated radicals to explain the observed spectra. The FOO radical was detected at low temperatures.