Poly(methyl methacrylate) (PMMA)/single-walled carbon nanotube (SWNT) composites were synthesized by the grafting of PMMA onto the sidewalls of SWNTs via in situ radical polymerization. The free-radical initiators were covalently attached to the SWNTs by a well-known esterification method and confirmed by means of thermogravimetric analysis and Fourier transform infrared spectroscopy. Scanning electron microscopy and transmission electron microscopy were used to image the PMMA-SWNT composites; these images showed the presence of polymer layers on the surfaces of debundled, individual nanotubes. The PMMA-SWNT composites exhibited better solubility in chloroform than the solution-blended composite materials. On the other hand, compared to the neat PMMA, the PMMA-SWNT nanocomposites displayed a glass-transition temperature up to 6.0 degrees C higher and a maximum thermal decomposition temperature up to 56.6 degrees C higher. The unique properties of the nanocomposites resulted from the strong interactions between the SWNTs and the PMMA chains. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 452-459, 2011