The melt grafting of vinyltriethoxysilane (VTEOS) to polyethylene using 2,3-dimethyl-2,3-diphenylbutane (bicumene) as a radical initiator is demonstrated and compared to conventional peroxide-initiated processes. A bicumene-initiated modification of high density polyethylene at 290degreesC provided no benefits in terms of selectivity when compared to a standard peroxide-based process operating at 180degreesC. However, the selectivity of linear low-density polyethylene modification was influenced by chain scission, which counteracted the molecular weight effects of macroradical combination. Reactive extrusion data as well as studies of bicumene decomposition kinetics suggest that initiation occurs through an auto-oxidation mechanism that is facilitated by the interaction of cumyl radicals with oxygen.