Playing with chemistry on sp2 carbon allotropes: domino reactions for tailor made functionalization

sp2 carbon allotropes, such as carbon black, carbon nanotubes and graphene related materials can be seen as made by graphene sheets differently assembled. The graphene sheet is the common feature in all the carbon allotropes and it is a substrate for performing chemical reactions. In the present work, functionalization reactions were performed,1-2 with the aim to introduce functional groups with heteroatoms such as oxygen and nitrogen, without altering the structure of the graphitic substrates. KOH was reacted with carbon black, carbon nanotubes and with a nanosized graphite with very high surface area (HSAG), higher than 300 m2/g. Polyhydroxylated carbon allotropes were obtained. Wide angle X-ray and Raman analyses showed that the bulk structure of the carbon allotropes remained substantially unaltered. In particular, the crystalline organization of infinite and ideal graphene layers and the interlayer distance, between the few of them stacked in crystalline domains, were the same as in pristine HSAG. Layers were then decorated with aldehydic groups, in ortho position with respect to the hydroxyl ones, by performing Reimer-Tiemann reaction under mild experimental conditions. Tuning of reaction conditions led to obtain Reimer-Tiemann /Cannizzaro domino reaction: edge functionalization of graphene layers was with benzylic alcohol and carboxy groups. The first examples of Reimer-Tiemann and domino Reimer- Tiemann/Cannizzaro reactions on graphene layers are here reported. Such functionalized carbon allotropes were the platforms for further reactions. Compounds based on natural rubber (NR) were prepared through latex blending of NR with polyhydroxylated HSAG. They revealed better filler dispersion and higher dynamic modulus than composites based on HSAG prepared from melt blending. Compounds were also prepared with polyhydroxylated carbon black and appreciable impact on dynamic mechanical properties was observed. Rubber compounds were also prepared with functionalized carbon allotropes with oxygen and nitrogen containing functional groups: vulcanization behaviour and mechanical reinforcement is discussed.