Single-walled carbon nanotubes functionalized with high bonding density of polymer layers and enhanced mechanical properties of composites

Single-walled carbon nanotubes (SWNTs) with high covalent bonding density of polymer layers have been prepared by a "grafting to" approach, where the benzyl chloride groups of styrene copolymers (M-n = 47 600) reacted with the alkyne groups on SWNTs under relatively mild conditions, resulting in a higher grafting efficiency, as high as 81 wt % of (TGA). Microscopic observations clearly displayed the uniform, thick polymer layers formed on the SWNT surface. The high density of covalent bonding between polymer and nanotubes was confirmed by Raman, H-1 NMR, and FTIR, which makes them well dissolved in organic solvents and homogeneously dispersed in polymer matrices. The in situ UV-vis observations during the dissolution indicated that for such a multifunctional system almost no cross-links occurred between SWNTs due to the physical absorption and steric hindrance of polymer chains during the functionalization of SWNTs. The functionalized SWNTs exhibited a pronounced effect on the mechanical properties of polystyrene composites. Only 0.06 wt % of SWNTs resulted in 82% and 78% of increases in tensile strength and elastic modulus of the composites, respectively, indicating an efficient interfacial stress transfer between SWNTs and polymer.