Samarium poly(oxamide) polyanions, formed quantitatively in situ by the reductive coupling polymerization of aromatic diisocyanates with samarium (II) iodide/hexamethylphosphoramide (HMPA) system, were directly used as the polymeric initiators in the graft polymerization with some electrophilic monomers. The graft polymerization of epsilon-caprolactone (CL) with several polyanions derived from bifunctional isocyanates, including tolylene 2,6-diisocyanate, o-tolidine diisocyanate and diphenylmethane diisocyanate, provided the corresponding graft copolymers in one-pot, indicating that the polyanion could work as a new type of reactive polymer. Several factors such as reaction temperature and time and the amount of HMPA and CL affected the behavior of the present polymerization system, and the graft copolymer was obtained quantitatively under the appropriate conditions. The results of the graft polymerizations of tertbutyl methacrylate and methyl methacrylate with the polyanion were also presented.