Facile and sustainable functionalization method for preparing graphene layers with different solubility parameters

Graphene has exceptional properties: high charge-carrier mobilities, in-plane thermal conductivity, very high elastic modulus. Such properties essentially arise from the six atoms aromatic ring repeating unit of graphene layers. Hence, objective of graphene synthesis and functionalization should be to obtain and preserve such structure. Graphene functionalization has indeed great importance: electronic and solubility properties, self-assembly and phaseforming behaviour are affected by functional groups. In this work, a functionalization method was developed (1,2), able to introduce functional groups in peripheral positions of graphene layers, without appreciably altering graphene structure. Functionalization was performed by using molecules whose basic structure is shown in Figure 1. A pyrrole ring with different substituents on the nitrogen atom was used. Synthesis of these molecules was performed with high atom economy (larger than 80%), high yield (up to 99%) and thus high atom efficiency, the only byproduct being water, in the absence of solvent and catalyst (3). Reaction between such molecules and nanosized high surface area graphites was performed by simply mixing them, donating either mechanical or thermal energy. Functionalization occurred with almost quantitative yield. This process has a low environmental impact. Thanks to such functionalization method, solubility parameter of graphene layer was changed in a broad range, obtaining stable layers’ suspension in water, hexane, toluene. Form such suspensions, few layers graphenes were isolated. Moreover, even dispersions of graphene layers were prepared in polymer matrices such as poly(1,4-cis-isoprene), poly(styrene-cobutadiene), poly(urethane). This work presents a facile, sustainable, economically viable functionalization method of graphene layers, suitable for preparing few layers graphene from nanosized graphite and for matching the solubility parameters of polymer matrices, achieving even dispersions and intimate interactions.