Multiwalled carbon nanotubes (MWNTs) with acyl chloride functional groups and a metallocene polyethylene-octene elastomer (POE) or an acrylic acid-grafted metallocene polyethylene-octene elastomer (POE-g-AA) were used to prepare hybrids (POE/MWNTs or POE-g-AA/MWNTs) using a melting method, with a view to identify a hybrid with improved thermal properties. Hybrids were characterized using Fourier transform infrared spectroscopy, C-13 solid-state nuclear magnetic resonance, X-ray diffraction, thermogravimetry analysis, and scanning electron microscopy. MWNTs were purified using acid treatment, and results showed that -COOH of MWNTs increased with acid treatment time and leveled off after 24-h treatment. Much better dispersion and homogeneity of MWNTs was obtained with POE-g-AA in place of POE as the matrix. As a result, tensile strength at break of POE-g-AA/MWNTs was significantly improved even at 5 wt % MWNT content. Moreover, temperature of thermal decomposition for POE-g-AA/MWNTs was about 40-50 degrees C higher than that for POE-g-AA, indicating higher thermal stability. This was because the carboxylic acid groups in POE-g-AA and the acyl chloride functional sites in MWNTs allow the formation of stronger chemical bonds. (c) 2007 Wiley Periodicals, Inc. J Appl Polyrn Sci 104: 1328-1337, 2007.