Atom transfer radical polymerization using activators regenerated by electron transfer (ARGET ATRP) of acrylonitrile with FeBr3 and isophthalic acid (IA) as catalyst and ligand, ascorbic acid (VC) as reducing agent, and ethyl 2-bromoisobutyrate as initiator was approached for the first time in the presence of air in 1-dodecyl-3-methylimidazolium tetrafluoroborate ([C(12)mim][BF4]), 1-octyl-3-methylimidazolium tetrafluoroborate ([C(8)mim][BF4]), and 1-butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BF4]). The rate of polymerization in [C(12)mim][BF4] was considerably faster than in [C(8)mim][BF4] and [C-4 mim][BF4]. With an increase of VC concentration, both the monomer conversion and the molecular weight distribution showed a trend of increase. Polyacrylonitrile (PAN) with higher molecular weight at 166,250 and broader distribution at 1.34 was successfully prepared with PAN as macroinitiator via ARGET ATRP in [C(12)mim][BF4] in the presence of air. The resultant polyacrylonitrile fibers were obtained with the fineness at 1.15 dtex and the tenacity at 6.24 cN dtex(-1). Additionally, it was shown that [C(12)mim][BF4] could be recycled and reused after simple purification and had no effect on the living nature of polymerization. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3298-3302, 2011