Photoinduced and Thermal Radical Conversions in γ-Irradiated Copolymers of Tetrafluoroethylene and Hexafluoropropylene as Studied by Electron Spin Resonance

Abstract

It was found that a perfluorinated tertiary-carbon radical ···CF2–Ċ(CF3)–CF2··· formed in γ-irradiated copolymers of tetrafluoroethylene and hexafluoropropylene is converted into the radical ···CF2–CF(ĊF)2–CF2··· by illumination of uv light at 77°K and the process is reversed by thermal annealing. This may be the first example of the photoinduced conversion of fluorocarbon radicals. The uv absorption spectra of perfluorinated tertiary-carbon radicals were also measured and a strong absorption was found at 2650 Å. The wavelength dependence of the radical conversion indicates that the photoisomerization of the tertiary-carbon radical is induced by the absorption of this light. The tentative assignment of the ESR spectra to the radical ···CF2–Ċ(CF3)–CF2··· in a previous paper was further confirmed by this experiment. In addition, it was found that γ irradiation at 77°K gives the radical ···CF2–CF(ĊF2)–CF2··· as a forerunner radical of the tertiary-carbon radical found in room-temperature irradiation.