Nanocomposites based on a sodium partially-neutralized ionomer of poly(ethylene-co-methacrylic acid) (EMAA) and MgAl layered double hydroxide (LDH) particles with and without organic modification were prepared from a melt mixing process. The structure was characterized using X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). Although TEM micrographies revealed the presence of agglomerates of LDH sheets, the achievement of an exfoliated structure was observed when dodecyl sulphate-modified LDH particles were used. The effects of the LDH particles on the thermomechanical properties of EMAA were analyzed using differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The thermal transition of the ionic aggregates and dynamic mechanical response of EMAA were found strongly modified by these particles, resulting in an increase on the storage modulus and a decrease on the loss factor values. Moreover, the alpha relaxation of the composites was visibly shifted to higher temperatures. (c) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2573-2579, 2010