Functionalization of Multiwalled Carbon Nanotubes by Atom Transfer Radical Polymerization and Defunctionalization of the Products

Abstract

A core−shell hybrid nanostructure, possessing a hard backbone of multiwalled carbon nanotube (MWNT) and a soft shell of brushlike polystyrene (PS), was successfully prepared by in situ atom transfer radical polymerization (ATRP), using Cu(I)Br/N,N,N',N'',N''-pentmethyldiethylenetriamine (PMDETA) as the catalyst, at 100 °C in diphenyl ether solution. The molecular weight of PS was well controlled, as was the thickness of the shell layer. TEM images of the samples provided direct evidence for the formation of a core−shell structure, i.e., the MWNT coated with polymer layer. FTIR, 1H NMR, SEM, and TGA were used to determine the chemical structure, morphology, and the grafted PS quantities of the resulting products. To further establish the covalent linkage between PS and MWNT moieties, the resulting PS-functionalized MWNTs were defunctionalized by hydrolysis or by thermal decomposition. Comparative studies, based on TEM and SEM images between the PS-functionalized and chemically defunctionalized MWNT samples, also revealed the covalent coating character. GPC analysis showed that the number-average molecular weight (Mn) of the grafted PS chains ranged from 5000 to 11 000 with a relatively broad polydispersity index (PDI, ca. 1.77−3.57). Further copolymerization of tert-butyl acrylate (tBA) with the PS-linked MWNTs as initiators was realized, illustrating that (1) the PS species is still "living" although the lower controllability of PDI and (2) acrylate-type monomers can be copolymerized with styrene-type ones on the sidewalls of the MWNT. We believe that achieving these hybrid objectives, on the basis of such simple grafting, will pave the way for the design, fabrication, optimization, and eventual application of more functional carbon nanotube-related nanomaterials.