P. Rapta, Andrea Vargová, J. Polovková
Sep 1, 2009
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Journal
Polymer Degradation and Stability
Abstract
Abstract Electrochemical and spectroscopic (EPR, UV–Vis, IR) studies of the aromatic secondary amines N , N ′-diphenyl-1,4-phenylenediamine (DPPD), N-phenyl- N ′-isopropyl- p -phenylene diamine (IPPD), N -phenyl- N ′-(α-methylbenzyl)- p -phenylenediamine (SPPD) and N -phenyl- N ′-(1,3-dimethyl-butyl)- p -phenylenediamine (6PPD), which represent the most important group of antioxidants used in the rubber industry, are presented. During oxidation, all the compounds show reversible redox couples in acetonitrile/0.1 M TBABF 4 . The first oxidation potential depends substantially on the R substituent at the –N′H– moiety. Very similar UV–VIS spectra of monocation radicals and dications for all the compounds were observed by applying anodic oxidation as well as oxidation by tert-butyl hydroperoxide both in air and in inert atmosphere. The samples with N ′-bonded aliphatic carbon in the molecule (e.g. IPPD) heated in air undergo consecutive chemical reactions leading to the formation of –N′ C– group. By the use of RO 2 radicals only very low concentration of nitroxide radicals was obtained. Very high concentration of nitroxide radicals was achieved using 3-chloroperbenzoic acid. In the oxidation of investigated aromatic secondary amines with powder PbO 2 no EPR spectra were observed and UV–Vis and IR studies indicate the rapid formation of the final dehydrogenated oxidation product.