Electron spin resonance studies of peroxy radicals labeled with ¹⁷O in polytetrafluoroethylene Available to Purchase

The ESR spectrum of the radicals formed by the reaction of oxygen with γ‐irradiated polytetrafluoroethylene (PTFE) has been obtained using oxygen isotopically labeled with ¹⁷O. The presence of lines from two oxygen nuclei both labeled with ¹⁷O confirms that peroxy radicals are formed. Two types of peroxy radicals are discussed; firstly, the peroxy chain radical (–CF₂–CF(O₁Ȯ₂)–CF₂) with g_⊥=2.0220, g_∥=2.0060, a_∥(1) =40±1 G, a_∥(2) =89±1 G at 300 K, and g_zz=2.0380, g_yy=2.0065, g_xx=2.0026, a_xx(1) =46±1 G, a_xx(2) =107±1 G at 77 K and secondly, the peroxy propagating radical (–CF₂–CF₂(O₁Ȯ₂)) with g_iso=2.004, a_iso(1) =13±1 G, a_iso(2) =26.5±1 G at 300 K and identical parameters to the peroxy chain radical at 77 K. The temperature dependence of the ESR spectra is analyzed in terms of the rotational freedom in the polymer. The peroxy chain radical undergoes rotation along the polymer chain axis and the peroxy propagating radical also has this rotation about the chain axis and in addition rotates about the C–O bond which is nearly perpendicular to the main chain axis.