Abstract
The main study was of the effect of n-butyl orthotitanate as a photo-initiator in the oxidation at 34· 5° of 2,4,6,8-tetramethylnonane (a liquid model for polypropylene) irradiated by u.v. light having, in the region 2900–3500 Å, a spectral distribution similar to that of the solar radiations reaching the Earth's surface. n-Butyl orthotitanate was chosen as a model for Ti(IV) compounds, left in polypropylene as catalyst residues after purification. It has been possible to establish that, at least for the conditions studied, 7 per cent of the photoexcited molecules of n-butyl orthotitanate undergo homolytic decomposition with generation of two butoxy radicals. 12 per cent of the butoxy radicals extract a tertiary hydrogen from the hydrocarbon, thus giving alkyl radicals which in turn start the auto-oxidation. Equations have been obtained giving the values of the overall oxidation rate of the hydrocarbon vs. the irradiation intensity and the concentration of the chromophore.
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