Poly(methyl acrylate)/Na-montmorillonite intercalated composites were prepared by free-radical polymerization using benzoyl peroxide as a radical initiator in an aqueous medium. XRD patterns confirmed that the increase in interlayer spacing of Na-montmorillonite (Na-MMT) from 1.21 to 1.64 nm supports the intercalation. Although the width of the intercalated, delaminated montmorillonite aggregates are less than 100 nm (as seen in transmission electron microscopy), the prepared samples are members of the intercalated composite group. The samples exhibited better thermal stability than the pure polymer. Nitrogen adsorption capacity decreased due to the hindering of molecule diffusion and shielding of the intercalated aggregates by the polymer matrix. The decrease in moisture and water uptake of the samples indicated that the hydrophilic nature of montmorillonite changed greatly due to the hydrophobicity with increasing polymer content. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 3662-3667, 2012