Functionalization of multiwalled carbon nanotubes with polyamide 6 by anionic ring-opening polymerization

Covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with polyamide 6 was accomplished by anionic ring-opening polymerization of ε-caprolactam in the presence of sodium caprolactamate as a catalyst and caprolactam functionalized MWCNTs as an initiator. The initiator precursor, isocyanate functionalized MWCNTs, was prepared by directly reacting commercial hydroxyl functionalized MWCNTs with excess toluene 2,4-diisocyanate. This anionic ring-opening polymerization was found to occur in a highly efficient manner at relatively low reaction temperature (170°C) and short reaction times (6h). FTIR spectroscopy was utilized to follow the introduction and consumption of isocyanate groups on the MWCNTs. Thermogravimetric analysis indicated that the polyamide 6 was successfully grown from the MWCNT surface, with the final products having a polymer weight percentage of ca. 40–65wt%. Transmission electron microscopy was utilized to image the polymer-functionalized MWCNTs, showing relatively uniform polymer coatings presented on the surface of MWCNTs.