Sustainable functionalization of sp2carbon allotropes

Carbon black, carbon nanotubes, graphene and graphene related materials: sp2 carbon allotropes are indeed available as efficient reinforcing fillers for rubber composites. In particular, nanometric fillers have the great potentiality to establish a large interfacial area with the polymer matrix, thus in principle promoting great enhancement of the composites’ properties, provided that a stable polymer-filler interaction is achieved. The functionalization of sp2 carbon allotropes can dramatically enhance their compatibility with the polymer matrix. In our research Group, objective was to design and develop sustainable functionalization methods for sp2 carbon allotropes. Common feature of the research was to move from natural sources, preparing then innovative building blocks and derivatives suitable for the functionalization reactions. In this contribution, examples will be reported. Pyrrole compounds (PyC) were obtained with high atom economy and yield from primary amines and α,δ dicarbonyl compounds. Functionalization was obtained by simply mixing a carbon allotrope and a pyrrole compound, giving thermal energy. Functionalization yields were up to 96%, the bulk structure of the graphitic substrates was not affected. Study of the mechanism led to identify a domino reaction involving a carbocatalyzed oxidation of the pyrrole compound followed by Diels-Alder cycloaddition. The synthesis of PyC was also performed in situ, on the carbon allotrope. Dispersions of functionalized carbon allotropes were prepared in solvents with different solubility parameters and, from the qualitative results of the dispersion tests, Hansen solubility parameters of carbon allotropes were estimated. Effect on vulcanization and mechanical properties of rubber composites is discussed.