Novel families of polystyrene carbon nanocomposites and graphene brushes were prepared by means of free radical styrene grafting using sulfur-functionalized graphene (S-FG) as macro-chain-transfer agent. Two strategies were examined for growing polystyrene chains onto graphite oxide (GO), stearylamine-modified GO (Stearyl-GO), and thermally reduced GO (TRGO): (i) chain transfer with novel thiol-functionalized graphenes and (ii) RAFT-mediated polymerization using dithiourethane-, dithioester- and dithiocarbonate-functionalized graphenes. Novel thiol-functionalized graphenes were obtained from FG either by esterification with 3-mercaptopropionic acid or by reaction with propylene sulfide. The styrene graft polymerization was initiated either with AIBN at 65 degrees C or by thermal styrene self-initiation at 130 degrees C. The graphene content, varying between 0 and 5.2 wt %, was determined by means of thermogravimetric analysis (TGA). Upon hydrolytic cleavage of the dithiocarbonate linker, the stability of the S-FG dispersion in polystyrene was lost, and the nonbonded S-FG was separated quantitatively from polystyrene by solvent extraction. During melt processing the graphene brushes self-assembled to produce nanoribbons and skeleton-like carbon superstructures, as determined by means of transmission electron microscopy (TEM). Both grafting effectiveness and superstructure formation were monitored by means of melt rheology.