The invention relates to a compound of formula (Ia), (Ib) or (Ic). The open chain alkoxyamine compounds are useful for the polymerization of ethylenically unsaturated monomers. The compounds of the present invention provide polymeric resin products having low polydispersity. The polymerization process proceeds with enhanced monomer to polymer conversion efficiency. In particular, this invention relates to stable free radical-mediated polymerization processes which provide homopolymers, random copolymers, block copolymers, multiblock copolymers, graft copolymers and the like, at enhanced rates of polymerization and enhanced monomer to polymer conversions.