EPR study of temperature dependent rotations of polytetrafluoroethylene chains labeled with peroxy radicals

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Abstract
The temperature dependence of the EPR spectra of peroxy chain radicals (R–CF2–CFOO ̇ –CF2–R′) and peroxy propagating radicals (R″CF2–CF2OO ̇) trapped in polytetrafluorothylene (PTFE) is studied in the range −196 °C, +300 °C, and analyzed in terms of the rotation freedom in the polymer. The peroxy propagating radical undergoes rotation along the polymer chain axis above −120 °C, whereas the peroxy chain radical has the same rotation but only above −20 °C. This difference is explained in terms of a particular mobility of the extremity of the carbon chain. Above −40 °C, the peroxy propagating radical rotates about the C–O bond in addition to the rotation about the chain axis. The additional rotation about the C–O bond is not observed below the decomposition temperature of the peroxy chain radical.