A synthesis method to prepare a fully grafted polydiphenylamine (PDPA) with poly(ethylene oxide) (PEO) through a "graft onto" process is reported. Three graft copolymers, PDPA-g-PEO-350, PDPA-g-PEO-750, and PDPA-g-PEO-2000, were obtained by substituting the tosyloyl end group of tosylate PEO with an amine-functionalized PDPA. The latter polymer was prepared via an acid-mediated chemical polymerization of diphenylamine. These graft copolymers became water-soluble when the grafted PEO molecular weight (M-n) was above 750. Furthermore, the copolymers can be oxidized, in aqueous acidic solutions in the presence of air, to produce PDPA in a conducting state, containing, depending on the degree of oxidation, the N,N'-diphenylbenzidine radical cation (DPB.+) or the N,N'-phenylbenzidine dication (DPB2+). The conductivities of the HCl-doped graft copolymers were found to be in the range 10(-1)-10(-4) S/cm, dependent on the grafted PEO side-chain length. As expected, the PDPA-g-PEO copolymers with longer PEO side chains possessed lower conductivities. Furthermore, for the HCl-doped PDPA-g-PEO-2000, the crystallization of the PEO-2000 side chains appears to be responsible for the low conductivity. Its conductivity could be raised 10-fold upon heating at 55 degreesC, above the PEO-2000 melting point (50 degreesC).