We describe a simple and novel method for dispersing multiwalled carbon nanotubes (MWCNTs) in a flexible epoxy matrix. The MWCNTs were modified with half-neutralized dicarboxylic acids having different numbers of carbon atoms. The modified MWCNTs were prereacted with epoxy in the presence of triphenylphosphine. The dispersion of the MWCNTs and the enhancement in the tensile properties were found to be better for composites prepared with a solvent. Among the half-neutralized dicarboxylic acids used, half-neutralized adipic acid (HNAA) exhibited the best performance. Scanning electron microscopy and transmission electron microscopy studies clearly indicated an improvement in the level of dispersion of the MWCNTs with the addition of the modifier. The good dispersion of the MWCNTs and the resulting improvement in their properties were attributed to the cation- interactions (the cation of HNAA and the -electron clouds of the MWCNTs) between the HNAA and MWCNTs and the chemical bonding of COOH groups of HNAA and the epoxy resin. The cation- interaction and chemical bonding was assessed with Fourier transform infrared spectroscopy and Raman spectroscopy. This approach did not destroy the -electron clouds of the MWCNTs in contrast to a chemical functionalization strategy. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2610-2618, 2013