Functionalization of carbon nanotubes with biodegradable supramolecular polypseudorotaxanes from grafted-poly(ε-caprolactone) and α-cyclodextrins

Functionalization of multiwalled carbon nanotubes (MWNTs) with biodegradable supramolecular polypseudorotaxanes has been successfully performed by utilizing surface-initiated ring-opening polymerization of ε-caprolactone (CL) to yield poly(ε-caprolactone)-grafted MWNTs (MWNT-g-PCL), followed by forming inclusion complexes between grafted-PCL chains and α-cyclodextrins (α-CDs) to give α-CD-NTPCL hybrids. There are significant differences in the morphology and solubility of MWNTs before and after introduction of α-CD. Some protuberances are clearly observed for α-CD-NTPCL as compared with MWNT-g-PCL. Furthermore, the host–guest stoichiometry (monomeric unit of CL/α-CD molar ratio) for α-CD-NTPCL is much higher than that of polypseudorotaxanes consisted of linear PCL and α-CDs. This observation can be explained by a combination of several reasons including the steric hindrance of grafted-PCL, the competitive exclusion between adjacent PCL chains toward α-CD, and the addition order of α-CD as well as the host–guest feed ratio. The present methodology may open up a new opportunity toward the application of supramolecular chemistry for the chemical manipulation and processing of CNTs. Moreover, such novel supramolecular hybrids provide an entry to extend the applications of CNTs to medicine and biology fields through embedding the functional polymers and heterogeneous components.