EPR studies of peroxide decomposition, radical formation and reactions relevant to cross-linking and grafting in polyolefins

EPR spectroscopy has been employed to detect directly radicals formed from a variety of polyolefins (PE, PP and EPM) during reaction with peroxide-derived alkoxyl radicals generated by thermolysis. Conditions have been chosen to reflect those employed in polyolefin grafting, degradation and cross-linking. Radical assignment is assisted, in particular, by the recognition of the effects of chirality on the β-proton hyperfine splittings. Quantitative analysis provides information on the selectivity of the initial attack (e.g. methine protons>methylene protons for PP); notable differences in selectivity between alternating EPM and other EPM samples are discussed. The detection of longer-lived allyl radicals detected for PE is explained in terms of alkyl radical disproportionation with subsequent reaction of the product alkene.