Multiwalled carbon nanotubes (MWNT) were functionalized with segmented polyurethanes (PU) by the "grafting to" approach. Raman and X-ray photoelectron spectroscopy (XPS) spectra show that the sidewalls of MWNTs have been functionalized with acid treatment, and the amount of COOH increases with increasing acid treatment time. FTIR and X-ray diffraction (XRD) spectra confirm that PU is covalently attached to the sidewalls of MWNTs by esterification reaction. Similar to the parent PU, the functionalized carbon nanotube samples are soluble in highly polar solvents, such as dimethyl sulfoxide (DMSO) and NN-dimethyfformamide (DMF). The functionalized acid amount and the grafted PU amount were determined by thermogravimetric analyses (TGA). Comparative studies, based on SEM images between the PU-functionalized and chemically defunctionalized MWNT samples, also reveal the covalent coating character. Dynamic mechanical analysis (DMA) of nanocomposite films prepared from PU and PU-functionalized MWNTs show enhanced mechanical properties and increased soft segment T.. Tensile properties indicate that PU-functionalized MWNts are effective reinforcing fillers for the polyurethane matrix. (c) 2007 Wiley Periodicals, Inc.