About antioxidant activity of hindered aliphatic amines and their derivatives to understand polyolefin stabilization at 25°C—I. Overall effects of SEC-hindered aliphatic amines and their nitroxyl derivatives on the kinetics of primary reactions of gamma-radiation-induced autoxidation of 2,4-dimethylpentane in the dark at 25°C compared with effects of a phenolic antioxidant

Abstract

The kinetics of the initial period of the 60Co γ-radiation-induced autoxidation in the dark at 25°C with I = 72 rad min -1 of well-oxygenated diluted solutions ( ca 3 × 10 -2 M) of 2,2,6,6-tetramethylpiperidine (TMPH) or bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate (HN—NH) in 2,4-dimethylpentane (DMP) showed that so-called sec-hindered alkylamine light stabilizers ( sec-HALS) are not primary antioxidants (AO). Their participation in the propagation reactions of the autoxidation of DMP includes the production of N-oxyl or nitroxyl (>NO ·) radicals. They also showed that sec-HAA are not hydroperoxide decomposers (secondary AO) at this temperature. The kinetics of the initial period of the γ-radiation-induced autoxidation under the experimental conditions mentioned above of well-oxygenated diluted solutions ( ca 3 × 10 -2 M) of the nitroxyl derivatives (TMPO · and ·ON—NO ·) of these sec-HA and of BHT (Ionol) which is a typical chain-breaking AO are very similar even though the mechanisms of action of these two kinds of inhibitors are quite different. The next papers of this series will deal with the relative inhibition effects of: (1) the trapping by > NO · of H · atoms and alkyl radicals produced by the radiolysis of DMP. The last lowers the rate of the radiation-induced autoxidation of DMP; (2) the chain-breaking AO properties of hindered hydroxylamines (>NOH) thus formed; (3) the search of any chain-breaking AO property, the mechanism of which at 25°C being still under discussion in the literature, of alkoxy hindered amines or hindered aminoethers (>NOR) also formed.