Values of kd for the C-ON bond homolysis were measured for alkoxyamines based on imidazoline and imidazole nitroxides. They were analyzed in terms of polar/stabilization, steric, and entropic effects, fed decreased with increasing electron-withdrawing capacities of the groups attached to the nitroxide, but increasing with both the bulkiness of the group attached to the nitroxide and the presence of substituents on the ring. With three alkoxyamines, it was shown that the fate of the NMP of styrene depended on the type of initiating alkyl radical: successful for initiating 1-phenylethyl radicals and unsuccessful for initiating p-nitrophenyloxycarbonyl-2-prop-2-yl radicals.