A Novel Method to Covalently Functionalize Carbon Nanotubes with Isocyanates
Tinh Nguyen, Aline Granier, Kristen L. Steffens, Hajin Lee, Naomi Eidelman, Jonathan W. Martin
We have developed a novel method to covalently functionalize carbon nanotubes (CNTs) that carry free isocyanate (N=C=O) groups. NCO-functionalized CNTs (NCO-fCNTs) are very desirable, because the NCO group is highly reactive with hydrogen-active groups, such as OH, COOH, and NH, which are commonly present in synthetic and natural polymers. The functionalization utilizes a di-isocyanate compound in which one NCO group has a higher reactivity than the other. By controlling the reaction parameters, the higher reactive NCO is allowed to react with hydrogen-active CNTs, while the less reactive NCO groups remain free. Both NCO-fSingle-walled CNTs (NCO-fSWCNTs) and NCO-fMulti-walled CNTs (NCO-fMWCNTs) have been successfully prepared using hydrogen-active carboxylic-terminated CNTs. Spectroscopic and thermal analysis results clearly showed that the functionalized CNTs bear a substantial amount of organic molecules and free NCO groups, and that the functionalization effectiveness is strongly dependent on catalyst concentration. The NCO-fCNTs have been shown to react readily with amines and polyols. Since the NCO group is highly reactive with a variety of natural and synthetic polymers, NCO functionalization potentially opens up many new applications of CNTs.