The controlled radical polymerization of styrene in water medium, in the presence of polyoxyethylene nonyl phenyl ether, catalyzed and initiated by CuCl/BDE [bis(N,N＇-dimethylaminoethyl)ether]/R-X was studied. The results show that the molecular weight increased with conversion of the monomer. Using this controlled system, the block copolymer, poly(St-b-MMA), was successful synthesized in water medium. In reference to the system of CuCl/BDE/PhCH2Cl, the polymerization may also occur in the micelle to produce a superhigh molecular mass (M-n = 1,500,000) polymer with monodispersion (MWD, M-w/M-n = 1.03). The Cu(I) and Cu(II) partition ratio in two phases, which may affect the reversible deactivation and debase the catalyst efficiency, was detected. (C) 2000 John Wiley & Sons, Inc.