EPR study of the rotational motion of the nitroxide radical embedded in polymers

Abstract

with X representing different functional groups was discovered. Study of the EPR spectra of nitroxide radicals in polymers is a means of widening the scope of the EPR method of investigating polymeric materials. Hitherto [2] the EPR method has mainly been used to study polymers under the influence of various physical effects, for example irradiation. At the same time it is often necessary to carry out the experiments at low temperatures as a rise in temperature would lead to the recombination of the unstable free radicals emerging as a result of the physical action. This temperature limitation is eliminated in the migration of stable nitroxide radicals into polymers (MNRP method). There are several reasons underlying the suitability of stable nitroxide radicals for polymer investigations. The CH 3 groups protect the unpaired electron of the nitroxide in chemical reactions [3, 4]. This accounts for its stability in different media as well as in the polymers under investigation. Another special feature of nitroxide radicals is the simplicity of the hyperfine interaction: the unpaired electron interacts mainly with the 14N nitrogen nucleus alone.t This makes it possible to interpret the EPR spectra within the framework of the Kubo-TomitaKivelson theory [5] and in this way to find the rotational motion of the radical embedded in polymers.