Examination of novel alkoxyamines has demonstrated the pivotal role that the nitroxide plays in mediating the "living" or controlled polymerization of a wide range of vinyl monomers. Surveying a variety of different alkoxyamine structures led to alpha-hydrido derivatives based on a 2,2,5-trimethyl-4-phenyl-3-azahexane3-oxy,1, skeleton which were able to control the polymerization of styrene, acrylate, acrylamide, and acrylonitrile based monomers. For each monomer set, the molecular weight could be controlled from 1000 to 200 000 amu with polydispersities typically 1.05-1.15. Block and random copolymers based on combinations of the above monomers could also be prepared with similar control.:In comparison with 2,2,6,6-tetramethylpiperidinoxy (TEMPO), these new systems represent a dramatic increase in the range of monomers that can be polymerized under controlled conditions and overcome many of the limitations associated with nitroxide-mediated "living" free radical procedures. Monomer selection and functional group compatibility now approach those of ATRP-based systems.