AbstractIn order to clarify the mechanism of catalysis of polyvinylamine‐copper(II) chelates on the initiation of vinyl polymerizations, stability constants of these chelates were measured by applying a modification of BJERRUM'S method, and each concentration of the chemical species was estimated on the basis of the chelate theory. From these results, the activity of the polyvinylamine‐copper(II) chelates for the polymerization of acrylonitrile and methyl methacrylate at different pH values was discus