A method utilizing generation of an alkyl iodide (low-mass dormant species) in situ formed in polymerization was adopted to reversible chain transfer catalyzed polymerizations (RTCP) (living radical polymerizations) with several nitrogen and phosphorus catalysts. The polymerization of methyl methacrylate afforded low-polydispersity polymers (M_w/M_n ~1.2–1.4), with M_n values predicted to high conversions; where M_n and M_w are the number- and weight-average molecular weights respectively. This method is robust and would enhance the utility of RTCP.