Without previous modification, single-walled carbon nanotubes (SWCNTs) react as dienophiles in a single-step Diels-Alder [4 + 2] cycloaddition with diene terminal polymer strands. Cyclopentadienyl-capped poly(methyl methacrylate) (M-n, = 2900 g mol(-1), PDI = 1.2) was grafted onto SWCNTs under mild conditions at ambient temperature as well as at 80 C in the absence of any catalyst. Thermogravimetric analysis, elemental analysis, and X-ray photoelectron spectroscopy confirm the success of the reaction and allow to estimate the grafting density of the polymer chains on the SWCNTs via the above three independent methods (average grafting density of 0.064 mmol g(-1) (0.029 chains nm(-2)) for samples reacted at ambient temperature and 0.086 mmol g(-1) (0.039 chains nm(-2)) for samples reacted at 80 degrees C). In addition, high-resolution transmission electron microscopy images confirmed the presence of an amorphous polymer layer (similar to 3 nm) around the SWCNTs after functionalization.