PROGRESS IN POLYMER SCIENCE, vol.24, no.8, pp.1149-1204, 1999 (SCI-Expanded)
Virtually all free-radical chain reactions require a separate initiation step in which a radical species is generated in the reaction mixture. Some types of chain reactions are initiated by adding a stable free radical, one that shows little or no tendency for self-combination, directly to the reactants, but a separate initiation step is still involved because these stable radicals are most often inorganic ions or metals.