A series of polystyrene-block-poly(4-(phenylethynyl)styrene) (PS-b-PPES) diblock copolymers with a range of compositions were prepared by reversible addition fragmentation chain transfer (RAFT) polymerization. Block copolymer/'cobalt carbonyl adducts (PSx-PPESy[ECo2(CO)(6)](n)) were subsequently prepared by reaction of Co-2(CO)(8) with the alkyne groups of the PPES block. Phase behavior of the block copolymer/cobalt carbonyl adducts (PSx-PPES)(y)[Co-2(CO)(6)](n), 18% <= wt % PS <= 68%) was studied by small-angle X-ray Scattering and transmission electron microscopy (TEM). As the composition of PSx-PPESy[Co-2(CO)(6)](n) copolymers Was shifted from PS as the majority block to PPESy[Co-2(CO)(6)](n) as the majority block, the morphology was observed to shift from lamellar with larger PS domains to cylindrical with PS as the minority component and then to spherical with PS as the minority component. These observations have been used to map out a partial phase diagram for PSx-PPESy[Co-2(CO)(6)](n) diblock Copolymers. Heating of PSx-PPESy[Co-2(CO)(6)](n) samples at relatiyely low temperatures (120 degrees C) results in the formation of nanoparticles containing, crystalline cobalt and cobalt oxide dornains within the PPESy[Co-2(CO)(6)](n) regions as characterized by TEM, X-ray diffraction (XRD), and X-ray scattering.