Interaction Between Polymer Chains Covalently Fixed to Single‐Walled Carbon Nanotubes

Abstract

AbstractSummary: A single‐walled carbon nanotube (SWNT), which had been oxidized with a mixture of nitric acid and sulfuric acid to afford polar groups at its ends, was incubated with an azo‐type macroinitiator carrying dextran (DEX), poly(ethylene glycol) (PEG) or poly(N‐vinylpyrrolidone) (PVPy) chains at 70 °C. Similarly, the oxidized SWNT was incubated with 2,2′‐azoisobutyronitrile and acrylic acid (HAA) or N‐vinylpyrrolidone at 70 °C. Due to the large radical trapping ability of SWNT, the polymer chains corresponding to the cloven macroinitiator (PEG, DEX or PVPy) and the propagating polymer chains (poly(acrylic acid) (HPAA) or PVPy) were covalently fixed to the surface of the SWNTs. The hydrophilic polymer‐modified SWNTs could be stably dispersed in water. Furthermore, the SWNTs modified with PEG and DEX sedimented in the presence of free DEX and PEG, respectively, whereas there was no precipitation of the PEG‐ and DEX‐modified SWNTs in the presence of the same kind of free polymer. This seemed to be related to the phase separation phenomena in water soluble DEX and PEG systems induced by the repulsive interaction between PEG and DEX molecules. However, the mixture of two kinds of polymer‐modified SWNTs (PEG‐SWNT and DEX‐SWNT) did not show noticeable phase separation, probably due to steric hindrance for the efficient repulsive polymer‐polymer interaction by fixation to the gigantic SWNTs. Furthermore, upon mixing the dispersions of HPAA‐SWNT and PEG‐SWNT or PVPy‐SWNT, the turbidity of the dispersions gradually increased, while no increase in turbidity of the dispersion mixture was observed in the presence of dimethyl sulfoxide, indicating hydrogen bonding between the HPAA and PEG or PVPy chains on the surface of the SWNTs. The modification methods examined in this work would be promising to give various functions to SWNT.Susceptible processes of radical trap on SWNT surface.imageSusceptible processes of radical trap on SWNT surface.