Dendritic polyarylether 2-bromoisobutyrates of different generations (Gn-Br, n = 1-3) as macroinitiators for the atom transfer radical copolymerization of N-hexylmaleimide and styrene in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate, were investigated. The copolymerization carried out in the ionic liquid with CuBr/pentamethyldiethylenetriamine as a catalyst at room temperature afforded polymers with well-defined molecular weights and low polydispersities (1.18, < M-w/M-n < 1.36, where M-w is the weight-average molecular weight and M-n is the number-average molecular weight), and the resultant copolymers possessed an alternating structure over a wide range of monomer feeds (f(1) = 0.3-0.8). Meanwhile, the copolymerization was also conducted in anisole at 110 degreesC under similar conditions So that the effect of the reaction media on the polymerization could be evaluated. The monolayer reactivity ratios showed that the tendency to form alternating copolymers for the two monomers was stronger in ionic liquids than in anisole.