Nanocomposites based on organically modified montmorillonites (OMMTs) and sodium montmorillonite (CLO-Na+) with poly(styrene-b-butadiene-b-styrene)(SBS) diblock copolymer have been investigated. Solution blending of OMMT suspension in toluene with SBS and Subsequent static casting and annealing resulted in transparent films. Final samples were processed by compression molding, The intercalation spacing in the nanocomposites, microphase separation of the SBS, and the degree of dispersion of nanocomposites were investigated by X-ray diffraction (Wide and small-angle X-ray scattering), transmission optical microscopy (TOM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The increase of basal spacing of OMMT in the nanocomposites suggested the intercalation of SBS. The lamellar structure perfection was extensively affected by both OMMT. AFM images and TOM micrographs only showed well dispersed but not exfoliated nanocomposite. On the other hand, TEM showed inserted tactoids into both blocks depending on the SUrfactant used (stained samples) and the dispersion of those tactoids (unstained samples). Fourier transform infrared spectroscopy indicated only the presence of the OMMT into the SBS. Deviations of hie decomposition pathway of pristine SBS with addition of the OMMT were found by thermogravimetric analysis. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3624-3637,2008