Functionalization of carbon nanotubes by atomic nitrogen formed in a microwave plasma Ar + N2 and subsequent poly(ε-caprolactone) grafting

Abstract

Multi-walled carbon nanotubes (MWNTs) are placed under atomic nitrogen flow formed through an Ar + N₂ microwave plasma in order to functionalize covalently their side walls with nitrogen-containing groups. The MWNT surface analyzed by X-ray photoelectron spectroscopy shows the presence of amides, oximes and mainly amine and nitrile functions grafted in this way. In order to highlight the actual location of the amine functions grafted on MWNTs, they were considered as initiation species in ring-opening polymerization of ε-caprolactone using triethylaluminium as activator. The so-generated poly(ε-caprolactone) chains remain grafted on the MWNTs via amide bonds and form polyester islets along the nanotubes surface. TEM images of these MWNT surfaces grafted with poly(ε-caprolactone) show a good amino-sidewall distribution. This work demonstrates the side-wall amino-functionalization of carbon nanotubes readily achieved by microwave plasma with the possibility to reach within a short time period very high contents in nitrogen-based functions (∼10 at.%).