Crosslinked poly(4-vinylbenzyl chloride) (PVBC) nanospheres of about 160 nm were first synthesized by emulsion copolymerization of 4-vinylbenzyl chloride (VBC) in the presence of a crosslinking agent, p-divinylbenzene. Subsequent modification of the nanosphere surfaces via surface-initiated atom transfer radical polymerization of 4-vinylpyridine, using the VBC units of PVBC on the nanosphere surface as the macroinitiators, produced a well-defined and covalently tethered poly(4-vinylpyridine) (P4VP) shells of 24-27 nm in thickness. Activation of the P4VP shells in a PdCl2 solution, followed by reactions with CO or H2S gas, gave rise to the corresponding P4VP composite shells containing densely dispersed palladium metal or palladium sulfide nanoparticles. The chemical composition of the nanosphere surfaces at various stages of surface modification was characterized by X-ray photoelectron spectroscopy. Field emission scanning electron microscopy and transmission electron microscopy were used to characterize the morphology of the organic/inorganic hybrid nanospheres coated with palladium/P4VP shells. (C) 2008 Wiley Periodicals, Inc.