Poly(methyl methacrylate) (PMMA)-clay nanocomposite (PCN) materials were synthesized through in situ intercalative polymerization. A cationic surfactant, [2(dimethylamino)ethyl]triphenylphosphonium bromide, was used as an intercalating agent with pristine Na+-mont-morillonite (MMT). The synthesized PCN materials were subsequently investigated by a series of characterization techniques, including wide-angle powder X-ray diffraction, Fourier transform IR spectroscopy, transmission electron microscopy, thermogravimetric analysis, and differential scanning calorimetry. Compared to pure PMMA, the PCN materials exhibit higher thermal degradation temperatures and glass-transition temperatures. The dielectric properties of PCN blending with a commercial PMMA material in film form with clay loading from 0.5 to 5.0 wt % were measured under frequencies of 100 Hz-1 MHz at 35-100 degrees C. Significantly depressed dielectric constants and losses were observed for these PCN-blending materials. (c) 2005 Wiley Periodicals, Inc.