Treatment of a diblock copolymer containing an alkyne-functional block (polystyrene-blockpoly(4-(phenylethynyl)styrene)) with dicobalt octacarbonyl (Co-2(CO)(8)) leads to selective incorporation of Co-2(CO)(6) groups in the alkyne block. Examination of these composites in bulk and thin films by transmission electron microscopy reveals the formation of ordered phase-separated morphologies typical of block copolymers. Heating the polymer-cobalt carbonyl adducts at moderate temperatures (110 degreesC) leads to loss of CO and formation of insoluble polymer cobalt composites. High-temperature thermolysis of these materials leads to formation of carbonaceous materials containing cobalt nanoparticles.