Effects of stabilized radicals upon polymerizations initiated by benzoyl peroxide

A study has been made of the inhibitory effects of diphenylpicrylhydrazyl and certain nitroxides upon systems at 60 °C involving benzoyl peroxide with methyl methacrylate, styrene or acrylonitrile. The pattern of results is rather different from that found in corresponding experiments with azobisisobutyronitrile as the source of radicals. When using the peroxide, relationship between duration of inhibition and the value of [inhibitor]/[peroxide] is in some cases far from linear; there is a dependence on the polarity of the diluent used for the reaction. It appears that there are probably direct reactions between the peroxide and the nitroxides which cannot therefore be regarded as ideal inhibitors in systems involving benzoyl peroxide. Products derived from the inhibitors affect the subsequent polymerizations. When the hydrazyl is used, the polymerizations following inhibition are retarded; the retardation is very slight in systems involving a nitroxide. For both types of inhibitor, the molecular weights of the polymers are quite low; the nitroxides differ from the hydrazyl in giving rise to poly(methyl methacrylate)ʹs having comparatively low values of M̄w/M̄n.