Judicious selection of bifunctional molecules to chemically modify graphene for improving nanomechanical and thermal properties of polymer composites

Covalently-functionalised graphene (FG) was successfully obtained by grafting m-isopropenyl-α, α′-dimethyl benzyl isocyanate (m-TMI) to graphene oxide (GO) followed by the chemical and solvothermal reduction of GO. The FG sheets were hydrophobic and stable in polar solvents such as N,N-dimethylformamide. The reactive vinyl-benzyl groups of m-TMI attached to FG copolymerised with methyl methacrylate to produce graphene/poly(methyl methacrylate) (PMMA) composites. The FG sheets were well dispersed in PMMA and formed strong interfacial bonds with the matrix, contributing to large increases in elastic modulus (+72.9%) and indentation hardness (+51.2%) at 1% loading by weight. The incorporation of FG into PMMA changed its elastic-plastic behaviour; hence, a decrease in the plasticity index and an increase in recovery resistance were observed for the resulting composites due to the increased portion related to the elastic work. The onset decomposition temperature and glass transition temperature of neat PMMA increased by 100°C and 12.7°C, respectively, by the addition of 1 wt% FG. Herein, in situ copolymerisation of monomers and well-suspended FG promotes the exfoliation of graphene associated with strong chemical bonding with the polymer matrix. This report provides a promising and facile method for fabricating high-performance polymeric composites.