Nitroxides having an alpha-carbon atom with a destabilizing moiety are effective control agents for emulsion and water-based polymerizations, including the formation of block copolymers from a wide range of monomers. The nitroxide radicals may be used as a free radical or as an adduct with a residue from the initiator. The emulsions have living characteristics, including the re-initiation of polymer chains. Also, a seeded process for emulsions, which includes the step-wise addition of monomer is disclosed, providing access to a wide range of initiator types.