Main-chain imidazolium-functionalized amphiphilic block copolymers (PIL-b-PS) consisting of polyionic liquid (PIL) and polystyrene (PS) blocks have been first synthesized by condensation polymerization combined with nitroxide-mediated free radical polymerization (NMP). The di-functional imidazolium-based ionic liquid (IL) having both hydroxyl and ester end groups was synthesized through Michael addition between imidazole and methylacrylate (MA) and further quaternization by 2-chloroethanol. The HTEMPO (4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy) terminated polyionic liquid (HTEMPO-PIL) as the hydrophilic block was prepared by condensation polymerization of di-functional imidazolium IL and HTEMPO at a certain ratio. The hydrophobic PS block was synthesized by controlled radical polymerization of styrene using HTEMPO-PIL through NMP, resulting PIL-b-PS block copolymers. The structure of block copolymers obtained has been characterized and verified by FTIR, 1H NMR, and size exclusion chromatography analyses. In addition, the morphology and size of the micelles formed by PIL-b-PS block copolymers in water were investigated by transmission electron microscopy and dynamic light scattering. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012