Poly (styrene-acrylonitrile) (SAN)/clay nanocomposites have successfully been prepared by melt intercalation method. The hexadecyl triphenyl phosphonium bromide (P16) and cetyl pyridium chloride (CPC) are used to modify the montmorillonite (MMT). The structure and thermal stability property of the organic modified MMT are, respectively characterized by Fourier transfer infrared (FT-IR) spectra, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The results indicate that the cationic

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... urfactants intercalate into the gallery of MMT and the organic-modified MMT by P16 and CPC has higher thermal stability than hexadecyl trimethyl ammonium bromide (C16) modified MMT. The influences of the different organic modified MMT on the structure and properties of the SAN/clay nanocomposites are investigated by XRD, transmission electronic microscopy (TEM), high-resolution electron microscopy (HREM), TGA and dynamic mechanical analysis (DMA), respectively. The results indicate that the SAN cannot intercalate into the interlayers of the pristine MMT and results in microcomposites. However, the dispersion of the organic-modified MMT in the SAN is rather facile and the SAN nanocomposites reveal an intermediate morphology, an intercalated structure with some exfoliation and the presence of small tactoids. The thermal stability and the char residue at 700 C of the SAN/clay nanocomposites have remarkably enhancements compared with pure SAN. DMA measurements show that the silicate clays improve the storage modulus and glass transition temperature (Tg) of the SAN matrix in the nanocomposites.