The efficient Cu(0) wire-catalyzed single-electron transfer-living radical polymerization (SET-LRP) of oligo(ethylene oxide) methyl ether methacrylate (OEOMA) in DMSO and binary mixtures of DMSO with H2O is reported. Addition of 10-80% H2O to DMSO resulted in an increase in the apparent rate constant of propagation ( kp app), corresponding to an increase in the polarity and extent of disproportionation. At higher H2O content, kp app decreases, and kp app in H2O is slightly lower than that in DMSO. This unexpected behavior was attributed to the physical inaccessibility of Cu(0) wire catalyst to the hydrophobic reactive centers of OEOMA and initiator which self-assemble in H2O into micellar aggregates and vesicles. This hypothesis was confirmed by the faster polymerization in H2O than in DMSO during catalysis with Cu(0) nanoparticles generated by disproportionation of CuBr. SET-LRP of OEOMA can be performed in protic and dipolar aprotic solvents in air by the addition of hydrazine hydrate. The polymerization exhibited no induction period and identical kp app as in the degassed experiment, and led to polymers with narrow molecular weigh distribution. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3110-3122