Fishing polymer brushes on single-walled carbon nanotubes by in-situ free radical polymerization in a poor solvent

Single-walled carbon nanotubes (SWNTs) exhibit unique thermal and electrical conductivity and high mechanical strength. The ability to effectively functionalize the SWNT surface and control their dispersion in a polymer matrix will be crucial to exploit their physical properties in nanocomposites. Here we report the first example of grafting polymers onto SWNTs in a poor solvent through a "fishing" process. The SWNTs act as "fishhooks", and the "living" polymer radicals are "fish", which are enthalpically favored to absorb onto the surface of SWNTs and continue to propagate until all the active sites are consumed. We demonstrate to graft 1 g of SWNTs with similar to 20 wt % poly(methyl methacrylate) in 100 mL of methanol/water (1/4 by volume) with monomer concentration as low as 5 mg/mL and monomer/SWNTs ratio of 0.5:1 by weight. The structure of functionalized SWNTs was characterized by Raman spectroscopy, UV-vis spectroscopy, HRTEM, and AFM. The polymer grafting method we described is fundamentally different from the reported approaches, where the polymerization takes place either solvent-free or in a good solvent but requires much higher monomer concentrations and monomer/SWNTs ratios. The promise of synthesizing gram-scale functionalized SWNTs from a wide range of polymers in a small volume of solvent may greatly improve our ability to engineer novel SWNT composites.