This paper reports a large scale production route for polystyrene (PS) nanoparticle-functionalized graphene sheets using water based in situ microemulsion polymerization. The higher surface area of the graphene basal plane and the better proximity of the reactant species in in situ microemulsion polymerization were used to functionalize the graphene sheets using PS nanoparticles. The thermal properties of the PS were improved with the incorporation of graphene in the composite. The modified graphene exhibited good compatibility and interactions with the host PS matrix to form conducting PS films. (C) 2010 Published by Elsevier Inc.