NEW TRENDS IN EPR AND EPR KINETICS STUDIES IN THE STABILIZATION MECHANISM BY N-OXYL RADICALS

The mechanism of the solid state oxidation of isotactic polypropylene films and the the mechanism of inhibition by HALS have been investigat ed by kinetic-ESR and kinetic modelling with derivation of the rate co nstants for the sensitive steps in the reaction scheme. The results ha ve shown the inadequacy of the Denisov cycle to account for the observ ed experimental kinetics of the intermediate nitroxyl radicals. The mo lecular dynamics associated with the oxidation inhibited by HALS in th e polypropylene matrix has been investigated by applying the Liouville stochastic method to the analysis of the temperature effects of the E SR spectra of the intermediate nitroxyl radicals used as spin probes. The investigation on the nature and characteristics of the molecular m otions available at the oxidation sites has also been carried out with nitroxyl spin labels bound to the PP chains. For this application a n ovel method of spin labelling was developed based on reactions with so me of the oxidation products, namely the terminal and intrachain keton es (Keana method), alcohols, peroxides and macroalkyl radicals.