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 P-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. (c) 2006 Elsevier Ltd. All rights reserved.