The radical trapping technique employing the stable nitroxide 1 as a scavenger has been used to study the reaction of ethoxyl radicals with methyl methacrylate and with styrene. The reaction of isopropoxyl radicals with styrene is also reported. The major pathway in all cases was addition to the unsubstituted (tail) end of the monomer. The data suggest that ethoxyl radicals should result in a much lower proportion of unsaturated end groups in poly(methyl methacrylate) than if t-butoxyl radicals are used to initiate polymerization. A possible example of a hydrogen atom transfer reaction from alkoxyl radicals is described.