AbstractThe anionic polymerization of 2‐pyrrolidone was accelerated with 1‐(1‐pyrrolin‐2‐yl)‐2‐pyrrolidone(1), labelled with nuclide15N. The incorporation of1into the polymer was followed by the change of isotope concentration, and the apparent rate constants were derived for some elementary reactions in the investigated polyreaction. The interchange reaction between1and monomer was also measured.1can be considered a slow activator, each molecule incorporating into the polymer being the precursor of a