Relationship between radical polymerization rate and initiator concentration in various solvents

Methyl methacrylate and styrene were polymerized by using 2,2′-azobis(2,4-dimethyl valeronitrile) as initiator in various solvents. When a poor solvent is used, the dependence of polymerization rate R_p on initiator concentration [C] is small and can be treated by equations for the analysis of the polymerization with primary radical termination. With a good solvent, the dependence of R_p on [C] is so large that such equations are not applicable. Thus, the [C] dependence in a good solvent is explained qualitatively through the molecular weight dependence of rate for termination between polymer radicals, based on the excluded volume effect.