Spintrapping of intermediateradicals in the solid state gamma radiolysis of perfluoropolyethers

Significant features of the mechanism of the solid state gamma radiolysis of perfluoropolyethers was elecidated by trapping of reactive radicalsintermediates as spin adducts with 2-Methylnitrosopropane (MNP) or in solid matrices at low temperature. Polyethers with repeating units -[(OCF2CF2)x(OCF2)-y]n (A), yield radicals of type ROCF2• and ROCF2CF2•, which are identified from their nitroxyls derivatives. Clear evidence for radical ROCF2• was also obtained from its polycrystalline spectrum. Polyethers of formula -[(OCF2CF(CF3))x-(OCF2)y−]n (B), yield radicals ROCF2Ċ(CF3)-, as major product, togheter with minor amount of ROCF2. The polycrystalline ESR spectrum of the pure compound show the presence of ROCF2• and ROĊF(CF3)- as major products whilst the tertiary radical is not observed. These observations suggest that prominent processes in the radiolysis of A are CC and CO bond homolysis followed by β scission of the resulting a alkoxy radicals. The same type of reaction may be invoqued to rationalize the formation of ROCF2• and ROĊCF(CF3) in the radiolysis of B; however the identification of the tertiary radical implies either the partecipation of a dissociative elctron capture during the irradiation or Fluorine abstraction by primay ROCF2• species during the warm up above 77 K. A slow thermal reaction of MNP with polyethers, yielding nitroxyls, has been observed and it is actually being investigated.