Characterization of Stable Nitroxide Radicals on the Basis of Adduct Chromophore-Hindered Amine Utilizing EPR Spectroscopy in Solution and Polymer Matrix

EPR spectra of 17 stable nitroxide radicals on the basis of 4-substituted 1-oxyl-2,2,6,6tetramethylpiperidine in solution (benzene) and in polymer matrices (PVC, iPP) were studied. Four derivatives containing pyrene and five with naphthalene as chromophore were used. They differ from each other by the length and type of bridge, connecting covalently the piperidine radical to chromophore. Two biradicals containing phosphorus and sulfur and one triradical containing phosphorus were investigated. In solution EPR spectra of probes containing one nitroxyl group provide triplet with line of equal intensity. The biradicals spectra were quintets and the triradical was septet. The purity of the prepared compounds was determined from the integrals of EPR spectra. In polymer matrices at room temperature the EPR spectra of monoradicals derived from hindered amines provide anisotropic spectra, typical for nitroxyl radicals in solid phase.