Water-soluble SWCNTs from sulfonation of nanotube-bound polystyrene

Polystyrene functionalized SWCNTs, prepared by copper(I) catalyzed click coupling of alkyne-decorated SWCNTs with well-defined, azide-terminated polystyrene, were transformed to water-soluble structures through sulfonation of the grafted polystyrene chains. The degree of polystyrene sulfonation was varied from 20 to 34 mol%, and was found to be directly proportional to the aqueous solubility of the material. The resulting sulfonated polystyrene-functionalized SWCNTs (SPS-SWCNTs) were found to be pH responsive, forming homogeneous solutions in water at pH values between 3 and 13. Outside of this pH range, the SPS-SWCNTs rapidly precipitate from solution. In addition, it was found that nanotube aggregation could be significantly reduced at high pH, where the sulfonate groups led to electrostatic repulsion between nanotubes.