The termination reaction in radical polymerizations. Polymerizations of methyl methacrylate and styrene at 25°

Styrene and methyl methacrylate have been polymerized at 25° using α,α′‐azo‐bis‐isobutyronitrile labeled with C 14 as initiator. The numbers of initiator fragments per polymer molecule have been determined by measurements of the average molecular weights of the polymers by osmometry and the specific activities of the polymers and the initiator by gas counting. It is found that polystyrene radicals combine at 25° and that for polymethyl methacrylate radicals at this temperature disproportionation occurs about twice as frequently as combination.