Polystyrene-block-poly(4-vinylpyridine) (PSb-P4VP) was synthesized by two steps of reversible addition-fragmentation transfer (RAFT) polymerization of styrene (St) and 4-vinylpyridine (4VP) successively. After P4VP block was quaternized with CH3I, PS-b-quaternized P4VP/montmorillonite (PS-b-QP4VP/MMT) nanocomposites were prepared by cationic exchange reactions of quaternary ammonium ion in the PS-b-QP4VP with ions in MMT. The results obtained from X-ray diffraction (XRD) and transmission electron microscopy (TEM) images demonstrate that the block copolymer/MMT nanocomposites are of intercalated and exfoliated structures, and also a small amount of silicates' layers remained in the original structure; differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) results show that the nanocomposites displayed higher glass transition temperature (T-g) and higher thermal stability than that of the corresponding copolymers. The blending of PS-b-QP4VP/MMT with commercial PS makes MMT to be further separated, and the MMT was homogeneously dispersed in the polymer matrix. The enhancement of thermal stability of PS/PS-b-QP4VP/MMT is about 20 degrees C in comparison with commercial PS. (c) 2006 Wiley Periodicals, Inc.