De novo growth of poly(amidoamine) dendrimers on the surface of multi-walled carbon nanotubes

Abstract

Carbon nanotubes (CNTs) are often used after modification. Poly(amidoamine) (PAMAM) dendrimers modified CNTs have attracted attentions due to their rich terminal amino groups. However, direct grafting of PAMAM dendrimers on CNTs’ surface is limited by the steric hindrance and its supply. De novo growth of PAMAM on multi-walled carbon nanotubes (MWCNTs), i.e., PAMAM@CNTs, is expected to eliminate the limits since the adopted reagents are readily available small molecular chemicals. It was realized using a divergent method and a “grafting from” technique by alternate amidization of terminal ester groups with ethylenediamine and Michael addition of methyl acrylate to the yielding amino groups. Spectral analysis, including Fourier transform infrared, Raman, hydrogen nuclear magnetic resonance, and X-ray photo-electron spectroscopy, verified that the functional groups were covalently grafted on the surface of MWCNTs, while thermogravimetric and elemental analysis showed that these groups were exponentially grown on MWCNTs, suggesting the formation of a dendritic PAMAM. Besides, high resolution transmission electron microscopy also confirmed that the spherical PAMAM was formed on the CNTs’ surface and an average particle size of 15–20 nm for G8.0-dendrimers was obtained.