Polymer-grafted multi-walled carbon nanotubes through surface-initiated ring-opening polymerization and click reaction

Multi-walled carbon nanotubes (MWNTs) are modified to possess the hydroxyl groups and are used as coinitiators to polymerize poly(ε-caprolactone) (PCL) or poly(α-chloro-ε-caprolactone) (PαClCL) by surface-initiated ring-opening polymerization. Pendent chlorides were converted into azides by the reaction with sodium azides. Finally, various types of terminal alkynes were reacted with pendent azides by copper-catalyzed Huisgen's 1,3-dipolar cycloaddition (click reaction). Chemical structure of resulting product and the quantities of grafted polymer were determined by Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS). High-resolution transmission electron microscopy (HR-TEM) images clearly indicate that the nanotubes were coated with a polymer layer. The MWNT-g-PCLs and MWNT-g-(PαN₃CL-g-alkyne)s are well dispersed in the organic solvent. The dispersability of MWNTs with grafted organic moieties is easier in CHCl₃ than in THF. The average thickness of the enwrapped polymer layer is approximately 8-10 nm for MWNT-g-PCL and 3 nm for MWNT-g- (PαN₃CL-g-PBA).