Green chemical functionalization of multiwalled carbon nanotubes with poly(ɛ-caprolactone) in ionic liquids

Multiwalled carbon nanotubes (MWNTs) have been successfully functionalized by free radical addition of 4,4′-azobis(4-cyanopentanol) in aqueous media to generate the terminal-hydroxyl-modified MWNTs (MWNT–OH), followed by surface-initiated in situ ring-opening polymerization of ɛ-caprolactone in 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF4) to obtain poly(ɛ-caprolactone)-grafted MWNTs (MWNT-g-PCL). Spectroscopic methods in conjunction with electron microscopy clearly revealed that hairy PCL chains were chemically attached to the surface of MWNTs to form core–shell nanostructures with the latter as core and the former as shell. With increasing polymerization time from 2 to 8 h, the amount of the grafted-PCL synthesized in BmimBF4 varies from 30.6 to 62.7 wt%, which is clearly higher than that (41.5 wt%) obtained in 1,2-dichlorobenzene under comparable conditions (8 h). The proposed methodology here uses water and room temperature ionic liquids (RTILs) as the reaction media and promises a green chemical process for functionalizing nanotubes.