  In order to realise the potential of graphene nanocomposites it is vital to
control the degree of dispersion and achieve a strong graphene polymer
interface. Herein, we developed a facile grafting to functionalisation approach
for graphene nanoplatelets. NH2-terminated graphene nanoplatelets, NH2 GNPs,
prepared by a diazonium coupling were used as a platform to covalently graft
PMMA chains to the surface of graphene through an amidation between the NH2
groups and PMMA chains, PMMA NH GNPs. A degree of PMMA grafting of 3.8 wt, one
chain per 40 carbon atoms, was found to both improve the dispersion of the GNPs
in a PMMA matrix and give strong graphene-polymer interfaces compared to
as-provided GNPs. Thus, 2 wt of PMMA NH GNPs in PMMA was found to increase the
elastic modulus, strength and strain at break of PMMA, whereas the
incorporation of unmodified GNPs showed poor levels of reinforcement at all
loadings. Furthermore, Tg and Td of PMMA were increased by 15 C and 29 C,
respectively, by adding 5 wt of PMMA NH GNPs, whereas incorporating unmodified
GNPs led to smaller increases. This work offers the possibility of controlling
the properties of graphene-polymer composites through chemically tuning the
graphene-polymer interface, which will have broad implications in the field of
nanocomposites.
