Functionalization of Single-Walled Carbon Nanotubes with Well-Defined Polystyrene by “Click” Coupling
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Covalent functionalization of alkyne-decorated SWNTs with well-defined, azide-terminated polystyrene polymers was accomplished by the Cu(I)-catalyzed [3 + 2] Huisgen cycloaddition. This reaction was found to be extremely efficient in producing organosoluble polymer-nanotube conjugates, even at relatively low reaction temperatures (60 degrees C) and short reaction times (24 h). The reaction was found to be most effective when a CuI catalyst was employed in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene as an additive. IR spectroscopy was utilized to follow the introduction and consumption of alkyne groups on the SWNTs, and Raman spectroscopy evidenced the conversion of a high proportion of sp(2) carbons to sp(3) hybridization during alkyne introduction. Thermogravimetric analysis indicated that the polymer-functionalized SWNTs consisted of 45% polymer, amounting to approximately one polymer chain for every 200-700 carbons of the nanotubes, depending on polymer molecular weight. Transmission electron microscopy and atomic force microscopy were utilized to image polymer-functionalized SWNTs, showing relatively uniform polymer coatings present on the surface of individual, debundled nanotubes.
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