Graphene's effect on the mechanism of radical polymerization with in situ graphene composites

Polymerizing a monomer in the presence of graphene/graphite is a common approach to making composites. However, the role played by the graphitic carbon in the polymerization is often poorly understood or neglected. Specifically, the polymer formed at the interface between the graphite and filler is expected to be most affected by the presence of the filler and can have an outsized effect on the composite properties. Herein we study the impact of pristine graphene on the polymerization of styrene during the synthesis of styrene/graphene nanocomposites. Although there is reason to expect that pristine graphene will interact with radicals, the difficulty of suspending graphene in solution has meant that experimental investigations have been limited to graphene nanoplatelets produced from microcrystalline graphite. However, microcrystalline graphite is fundamentally different than flake graphite, possessing more defects and sheets of limited lateral dimension. We overcome this challenge and study graphene obtained from natural flake graphite using interfacial exfoliation and graphene trapping. We find that graphene plays an active role in radical polymerization, acting as a chain transfer agent. At high graphite/graphene loading, it reversibly couples growing chains, lowering the value of the dispersity (Ð) relative to controls without graphene by nearly an order of magnitude.