Nearly monodisperse CdSe nanoclusters, surface-passivated with a layer of trioctylphosphine and trioctylphosphine oxide, have been sequestered within phosphine-containing domains in a diblock copolymer. A convergent approach to fabrication of these composites was adopted via independent synthesis of nanoclusters and polymer. Diblock copolymers of phosphine- or phosphine oxide-functionalized monomers and methyltetracyclododecene (MTD) were prepared by ring opening metathesis polymerization using Mo alkylidene initiators. Nanoclusters were prepared by pyrolysis of CdMe(2) and Se=P(octyl)(3) in the presence of P(octyl)(3) and O=P(octyl)(3). An immediate and sustained increase in electronic passivation is found for nanoclusters incorporated into octylphosphine-containing polymers. In contrast, nanoclusters in pure hydrocarbon or phosphine oxide-containing polymers rapidly lose passivation. Films of nanoclusters in a phosphine-containing polymer matrix were static cast from dilute solution. Under suitable conditions, the copolymers underwent microphase separation, and the metal chalcogenide clusters were predominantly sequestered within the phosphine-containing microdomains. The original, highly uniform cluster size distribution was unaffected.