RAFT polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA, 1100 g mol(-1)) was first performed using cyanoisopropyl dithiobenzoate (CPDB). The control of PEGMA homopolymerization, carried out in THF ([PEGMA] = 40 wt %) at 65 degrees C (reflux) using 2,2'-Azobis(isobutyronitrile) (AIBN) as initiator, was shown by the linear increase of molar masses and the low polydispersity indices (PDI) observed with conversion and also by the determination of a high chain transfer constant (C-tr = 9.1) for CPDB in this system. Copolymerization of PEGMA with methacrylic acid (MAA) ([PEGMA]/[MAA] = 40/60) was then undertaken first in dioxane at 85 degrees C. High conversion (89%) was obtained in 3 h without any composition drift and with a good level of control (PDI < 1.40). When the polymerization was performed in water, a strong increase in polymerization rate was observed with almost quantitative conversion (98%) in 2 h without affecting the level of control of the final copolymers (PDI similar to 1.30). These last results were tentatively explained by the formation of hydrophobic domains in which the polymerization occurred as in bulk. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3045-3055, 2009