Li and Zn ionomers of poly(ethylene-co-methacrylic acid) were modified by two organically modified montmorillonites by melt mixing. In the nanocomposites (NCs), the increase in the loss tangent main peak temperature indicated a reduction in the mobility of the long-chain segments Containing neutralized acid groups. The stack compaction observed by wide-angle X-ray scattering and transmission electron microscopy in the Cloisite 30B c based NCs was attributed to the partial degradation of the surfactant and to the irreversible character of the ion-exchange process of the ammonium cation of the surfactant with the Li cation. The considerable dispersion that occurred in the poly(ethylene-co-methacrylic acid) zinc salt (PEMA-Zn)/Cloisite 20A (20A) NCs was attributed to the high volume of the surfactant, which reduced undesired interactions between the inorganic clay surface and the ionomer. The ductile nature of the matrix remained in all of the NCs, and the increase in the modulus of elasticity of the PEMA-Zn/20A NCs reached a value five times greater than that of the PEMA-Zn matrix. The results Suggest that this ionomer is suitable for use both as a matrix for 20A NCs and as a compatibilizer of polyolefin-based NCs with 20A. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2374-2383, 2010