An iodine-based initiator, 2-iodo-2-methylpropionitrile (CPI), was utilized for the single-electron transfer and degenerative chain transfer mediated living radical polymerization (SET-DTLRP) of methyl methacrylate (MMA) in the absence of ligand, at ambient temperature. The CPI-initiated ligand-free polymerizations manifested reasonable control over molecular weights with relatively narrow distributions (Mw/Mn 1.35). The living nature of the polymers was further confirmed by successful chain extension reaction and 1H NMR with high chain-end fidelity (approximate to 96%). Screening of the available solvents suggested that the controllability of this polymerization was highly dependent on the kind of solvents, wherein dimethyl sulfoxide was a better solvent for a controlled molecular weight. The proposed ligand-free SET-DTLRP initiated by CPI was intriguing since it would dramatically decrease the concentration of Cu(0) ions both in polymerization system and resultant polymer, and provided a more economical and eco-friendly reversible-deactivation radical polymerization technique. (c) 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013, 51, 1872-1879