Polymeric forms of ionic liquids may have many potential applications because of their high thermal stability and ionic nature. They are generally synthesized by conventional free-radical polymerization. Here we report a living/controlled free-radical polymerization of an ionic liquid monomer, 2-(1-butylimidazolium-3-yl)ethyl methacrylate tetrafluoroborate (BIMT), via atom transfer radical polymerization. Copper bromide/bromide based initiator systems polymerized BIMT very quickly with little control because of fast activation but slow deactivation. With copper chloride as the catalyst and trichloroacetate, CCl4, or ethyl alpha-chlorophenylacetate as the initiator, BIMT was polymerized at 60 degreesC in acetonitrile with first-order kinetics with respect to the monomer concentration. The molecular weight was linearly dependent on the conversion. The monomer concentration strongly affected the polymerization: a low monomer concentration caused the polymerization to be incomplete, probably because of catalyst disproportionation in polar solvents. The addition of a small amount of pyridine suppressed such disproportionation, but a further increase in the amount of pyridine greatly slowed the polymerization. (C) 2004 Wiley Periodicals, Inc.