Chemistry of Irradiation Induced Polytetrafluoroethylene Radicals: I. Re-examination of the EPR Spectra

Abstract

The electron paramagnetic resonance (EPR) spectra of the radicals formed during the γ irradiation of polytetrafluoroethylene (PTFE) are examined and assigned. It is shown that both chain radicals (e.g., RCF2CFCF2R) and propagating radicals (e.g., RCF2CF2·) are formed and stabilized when PTFE is irradiated in vacuum and at room temperature; the yield of the chain radical is 10 times that of the propagating radical. When PTFE is irradiated in air, the peroxide radicals RCF2CFOO·CF2R and RCF2CF2OO· are stabilized. The difference in yields of the two peroxide radicals is a function of total dosage, with the relative contribution of RCF2CF2OO· increasing with increasing dose. Both of the peroxide radicals are converted to the RCF2CF2· radical when they are irradiated with ultraviolet light (λ=280±20 mμ) in vacuum. Some chain radical is produced by the photolysis of its peroxide, but the yield of the propagating radical is 50 times that of the chain radical. The EPR spectrum of the RCF2CF2· radical consists of three sets of lines. The central set is a well-resolved triplet with a splitting between adjacent lines of 16±0.5 G. The wing lines are broadened by anisotropic nuclear hyperfine interactions, and the expected triplet structure is not resolved. From the room-temperature spectrum, it is estimated that the isotropic component of the α-fluorine interaction is ∼85 G. Also, from the 77°K spectrum, it is estimated that the maximum anisotropic component of the hyperfine interaction tensor is ∼140 G. The g value for this radical is 2.0038±0.0001.