Initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) with ppm amount of Cu catalyst was successfully developed in water. For the first time, Cu catalyst concentrations of 100 ppm and lower were used in aqueous media to prepare well-defined macromolecules. Polymers of oligo(ethylene oxide) methyl ether acrylate were synthesized with low dispersity (M-w/M-n = 1.15-1.28) using 20-100 ppm of an active CuBr/tris(pyridin-2-ylrnethyl)amine-based catalyst in the presence of excess bromide anions. This technique was used to synthesize a thermoresponsive block copolymer of poly(oligo(ethylene oxide) methyl ether methacrylate)-b-poly(oligo(ethylene oxide) methyl ether acrylate). The methacrylic block had a lower critical solution temperature (LCST = 77 +/- 2 degrees C) below that of the acrylic block. The hydrodynamic diameter of ca. 10 nm at temperatures below the LCST is consistent with free polymer chains in solution, and the diameter of ca. 30 nm above the LCST is consistent with a micellar structure. The aqueous ICAR ATRP technique was also used to successfully synthesize a well-defined bioconjugate by growing poly(oligo(ethylene oxide) acrylate) from a bovine serum albumin (BSA) protein functionalized with ca. 30 ATRP initiating sites.