The ambient temperature (20 degrees C) reversible addition fragmentation chain transfer (RAFT) polymerization of several water-soluble monomers conducted directly in aqueous media under gamma-initiation (at dose rates of 30 Gy h(-1)) proceeds in a controlled fashion. Using functional trithiocarbonates, i e.. S,S-bis(alpha,alpha'-dimethyl-alpha ''-acetic acid) trithiocarbonate (TRITT), 3-benzylsulfanyl thiocarbonylsulfanyl propionic acid (BPATT). and dithioester, i e, 4-cyanopentanoic acid dithiobenzoate (CPADB), as chain transfer agents, fully water-soluble polymers of monomers such as N,N-dimethylacrylamide, 2-hydroxyethyl acrylate, acrylamide or oligo(ethylene glycol) methacrylate and stimuli-responsive polymers of monomers such as acrylic acid. N-isopropylacrylamide, 2-(dimethylamino)ethyl methacrylate or 2-acrylamido-2-methylpropane sulfonic acid can be obtained over a wide range of degrees of polymerization up to 10,000 with low polydispersity (typically (M) over bar (w)/(M) over bar (n) < 1 2) to near quantitative conversions Well-defined block copolymers between these monomers, based on several asymmetric macro-RAM agents, can be obtained, suggesting that the RAFT agents are stable throughout the polymerization process so that complex and well-defined architectures can be obtained. (C) 2010 Elsevier Ltd All rights reserved.