The preparation and characterizations of new hybrid organic-inorganic nanocomposites consisting of acrylonitrile-butadiene-styrene terpolymer and a Na+-exchanged montmorillonite (MMT) are described by direct intercalation through onestep emulsion polymerization. Those products were purified by successive hot acetone and toluene extraction, respectively, for more than 2 days. The IR spectra for the purified samples revealed the characteristic absorbances as a result of those of styrene, butadiene, acrylonitrile, and MMT. X-ray diffraction spectra of the composites showed the enlarged 001 d-spacing as much as 1.75 nm, but no signals were found for the partial insertion of copolymer chains. Moreover, it was evident that this direct intercalation was not accompanied by delamination of the clay interlayer. The thermogravimetric analytic measurement for the purified product confirmed that the onset temperature of decomposition was transferred to the higher temperature region as much as 40-50 degreesC. Morphological observations by transmission electron microscopy, scanning electron microscopy, and optical micrography demonstrated homogeneous dispersion of MMT particles in the copolymer matrix. The possible physical picture of this direct intercalation was discussed in terms of swelling characteristics of compacted bentonite and the monomer containing micelle sizes. (C) 2001 John Wiley & Sons, Inc.