Carbon monoxide will be formed rather than carbon dioxide.

The mechanism of the solid state oxidation of isotactic polypropylene films and the the mechanism of inhibition by HALS have been investigated by kinetic‐ESR and kinetic modelling with derivation of the rate constants for the sensitive steps in the reaction scheme. The results have shown the inadequacy of the Denisov cycle to account for the observed experimental kinetics of the intermediate nitroxyl radicals. The molecular dynamics associated with the oxidation inhibited by HALS in the polypropylene matrix has been investigated by applying the Liouville stochastic method to the analysis of the temperature effects of the ESR spectra of the intermediate nitroxyl radicals used as spin probes. The investigation on the nature and characteristics of the molecular motions available at the oxidation sites has also been carried out with nitroxyl spin labels bound to the PP chains. For this application a novel method of spin labelling was developed based on reactions with some of the oxidation products, namely the terminal and intrachain ketones (keana method), alcohols, peroxides and macroalkyl radicals.

An initial study has been made of radiation-induced oxidation of polypropylene (PP) in both its additive-free form and one containing discrete amounts of stabilizer (HALS). Samples of PP were irradiated in a ''CO y source to various doses. This took place in either room air to give in-source oxidation or in vacuum at 77 K to render post-irradiation oxidation when the material was exposed to room air following irradiation. Studies were made of the chemical structure of the material and its concomitant dielectric behavior in terms of loss at low frequencies and thermallystimulated discharge current (TSDC). The polar functional groups induced via irradiation were observed to affect the dielectric response of the material, with the introduction of HALS reducing the concentration of gamma-induced oxidation products and the magnitude of the corresponding electrical signals.

No abstract

No abstract