Novel ionic liquids, [C(12)mim][BF4], [C(8)mim][BF4] and [C(4)mim][BF4], were firstly used as the reaction media for reverse atom transfer radical polymerization of ethyl acrylate (EA) initiated by azobisisobutyronitrile (AIBN) with CuBr2 and N,N,N',N",N"-pentamethyl diethylene triamine (PMDETA) as catalyst and ligand. Compared with the polymerization in [C(8)mim][BF4] and [C(4)mim][BF4], the polymerization in [C(12)mim][BF4] not only showed better control of molecular weight and narrower molecular weight distribution but also provided more rapid reaction rate with the ratio of [EA]:[AIBN]:[CuBr2]:[PMDETA] at 400:1:3:4. Block copolymer PEA-b-PSt was obtained via a conventional ATRP process in [C(12)mim][BF4] by using the resulting PEA as macroinitiator. [C(12)mim][BF4] and CuBr2/PMDETA could be easily recycled and reused and had no effect on the living nature of reverse atom transfer radical polymerization of EA. (C) 2008 Elsevier B.V. All rights reserved.