1991±96) investigations devoted to the subject, the fol- lowing conclusions can be proposed regarding the mechanism of radiolysis of poly(per¯uoroethers): . The prevalent radiolytic events are C±C and C±O bond scissions leading to a decrease of the average molecular weight Mn and to changes in the chemical structure of the chains which have been identi®ed. Of minor importance is the splitting of C±F bonds. . Through the C±C and C±O scissions a variety of in- termediate per¯uoroalkoxyalkyl radicals are gener- ated which have been identi®ed and characterised by matrix ESR and ESR-spin trapping. . No evidence of trapped electrons could be obtained either by matrix ESR and uv/vis spectroscopy at 77 K, or by pulse radiolysis in the solid and ¯uid state. (On the contrary, trapped electrons are readilyobserved in the irradiated non-¯uorinated polyether analogues). However, the presence of charged species of macromolecular size is revealed by RTL emissions at the ``melting'' of the matrices on warming after gamma irradiation at 77 K. . The experiments of electron scavenging with CF3Br showing a decrease of 5±25% in the yields of the neutral free radical intermediates support the hypothesis that both charged and excited species contribute to the overall radiolysis process, the excitation mechanism being, however, of prominent importance. . No direct evidence of the presence of the poly- (per¯uoroether) cation and anion radicals following irradiation at 77 K could be obtained by ESR. MNDO-PM3 calculations and low temperature matrix ESR experiments of electron capture and electron loss performed with model compounds have a orded evidence of the intrinsic instability of these species which decompose undergoing mainly C±C bond scissions b to oxygen (radical cations) and C±C and C±O scissions (radical anions) with for- mation of neutral free radicals and diamagnetic ions.
File in questo prodotto:
Non ci sono file associati a questo prodotto.