Redox Initiators

Peroxy compounds, both organic and inorganic, became well-estabilished initiators of free-radical polymerization during the period 1920–1940, but a new chapter in their history opened in 1940 with the discovery that addition of small quantities of a reducing agent greatly increased the rate of initiation.1–4 An interesting review by Bacon4 describes the early history of redox initiation. Initiators composed of mixtures of oxidizing and reducing agents, now termed redox initiators, have become very important, particularly in industry where they are used extensively in low-temperature emulsion polymerization, for example in synthetic rubber production. The activation energies for radical generation by redox processes are often low, of the order 40 kJ mol−1 (compared to 130 kJ mol−1, approximately, for simple thermal dissociation into initiating radicals) so that they are particularly suitable for low-temperature polymerizations.