Homogeneous controlled free radical polymerization in aqueous media

The ability to conduct controlled radical polymerizations (CRP) in homogeneous aqueous media is discussed. Three main techniques, namely stable free radical polymerization (SFRP), with an emphasis on nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT) are examined. No examples exist of homogeneous aqueous NMP polymerization, but mixed water/solvent systems are discussed with specific reference to the NMP of sodium 4-styrenesulfonate. Aqueous ATRP is possible, although monomer choice is limited to methacrylates and certain styrenics. Finally, homogeneous aqueous RAFT polymerizations are examined. We demonstrate the greater versatility of this technique, at least in terms of monomer variety, by discussing the controlled polymerization of charged and neutral acrylamido monomers and of a series of ionic styrenic monomers. Many of these monomers cannot/have not been polymerized by either NMP or ATRP.