Grafting of adipic anhydride to carbon nanotubes through a Diels-Alder cycloaddition/oxidation cascade reaction

Accepted Manuscript

Different reactions have been reported for the successful functionalization of carbon nanotubes (CNT). The Diels-Alder cycloaddition is recognized as a plausible chemical approach, but few reports are known where this strategy has been used. In this study, the functionalization was performed by 1,3-butadiene generated from 3-sulfolene under heating conditions in diglyme. This simple and easily scalable method resulted in functionalized CNT with mass losses of 10 - 23 % by thermogravimetric analysis (nitrogen atmosphere). The functionalization was also supported by acid-base titration, elemental analysis, temperature programmed desorption and X-ray photoelectron spectroscopy. The high content in oxygen detected on the CNT surface was assigned to anhydride formation due to a cascade oxidation of the alkene groups generated in the cycloaddition reaction. The complete evolution of the alkene leads to a grafting density of 4.2 mmol g-1 for the anhydride moiety. Ab-initio calculations in CNT model systems indicate that the Diels-Alder addition of butadiene is a feasible process and that subsequent oxidation reactions may result in the formation of the anhydride moiety. The presence of the anhydride group is a valuable asset for grafting a multitude of complex molecules, namely through the nucleophilic addition of amines.

Centro de Química and Instituto de Polímeros e Compósitos of the University of Minho and Fundação para a Ciência e Tecnologia (FCT) through the Portuguese NMR network (RNRMN), the Project F-COMP-01-0124-FEDER-022716 (ref. FCT PEst-C/QUI/UI0686/2011) FEDER-COMPETE, Project PEst-C/CTM/LA0025/2013 (Strategic Project - LA 25-2013-2014) and also Project Scope UID/CEC/00319/2013. TG Castro acknowledges FCT for a doctoral grant (SFRH/BD/79195/2011) RF Araújo for a Post-doc grant (SFRH/BPD/88920/2012) and MMF also acknowledges FCT through the program Ciência 2008. Access to computing resources funded by the Project "Search-ON2: Revitalization of HPC infrastructure of UMinho" (NORTE-07-0162-FEDER-000086) is also gratefully acknowledged.