The atom transfer radical copolymerization of N-substituted maleimides such as N-phenylmaleimide (PhMI), N-cyclohexylmaleimide (ChMI), and N-butylmaleimide (NBMI) with styrene initiated with dendritic polyarylether 2-bromoisobutyrates in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), at room temperature and anisole at 110 degreesC was investigated. The dendritic-linear block copolymers obtained in ionic liquid possessed well-defined molecular weight and low polydispersity (1.05 < M-w/M-n < 1.32) and could be used as a macroinitiator for chain-extension polymerization, suggesting the living nature of the reaction system. The ionic liquids containing catalyst could be recycled in the atom transfer radical polymerization systems without further treatment. Compared with polymerization conducted in anisole, the polymerization in ionic liquid had a stronger tendency for alternation. The tendency for alternation decreased in the order PhMI > NBMI > ChMI in [bmim][PF6] and PhMI > ChMI > NBMI in anisole. (C) 2003 Wiley Periodicals, Inc.