Grafting of copolymers onto graphene by miniemulsion polymerization for conductive polymer composites: improved electrical conductivity and compatibility induced by interfacial distribution of graphene

A facile and general method to covalently functionalize graphene oxide (GO) with copolymers, using poly(styrene-co-methylmethacrylate) (P(St-co-MMA)) as an example, via miniemulsion polymerization is described in this study. After in situ reduction, insulating GO is converted to conductive reduced-graphene oxide (RGO). P(St-co-MMA) grafted RGO as conducting filler was incorporated into immiscible polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend to prepare conductive polymer composites (CPCs). The lowest percolation threshold (0.02 vol%) among all the reported values for graphene-filled CPCs was achieved due to the controllable preferential distribution of the modified RGO at the interfacial region between PS and PMMA phases, attributed to P(St-co-MMA) grafted on the surface of RGO behaving as compatibilizers to improve interfacial interactions with both the two phases. Moreover, P(St-co-MMA) grafting modified RGO could obviously enhance the compatibility reflected by a significant reduction of the size of dispersed phase, for an example, by nearly one order of magnitude for PS/PMMA (4/1 in volume) blends.