Exfoliated polystyrene (PS)/magadiite nanocomposites with a high suppression effect on thermal degradation were successfully prepared by in situ nitroxide-mediated radical polymerization of styrene monomer from the magadiite interlayer surface. Surface-initiated polymerization of styrene was conducted from the radical initiators immobilized on magadiite at 398 K. The number-average molecular weight (M n ) of the grafting PS increased with monomer conversion keeping a relatively low polydispersity index. The initiator efficiency was estimated to be less than 10% by size exclusion chromatography analysis. The results of X-ray diffraction and transmission electron microscopy suggested that the nanocomposites provided exfoliated structures. The fine dispersion state of magadiite in PS matrices contributed to effective suppression of the thermal degradation of PS. In addition, an interesting difference in the shape of the final residues was observed. Thermal decomposition of exfoliated PS/magadiite nanocomposites gave a substantial rigid solid as a residue, the shape of which largely depended on the concentrations of magadiite in the PS matrices. For instance, the thermal decomposition of nanocomposites produced a seamless residue that can effectively retard the decomposition rate. In contrast, the simple mixture of PS and magadiite was thermally decomposed to be powdery ash in the final residues.

A layered hydrous sodium silicate mineral, 'magadiite,' was uniformly exfoliated into polystyrene (PS) matrices to result in a PS/magadiite nanocomposite with high flame-retardant properties. Surface-initiated radical polymerization of styrene from the magadiite interlayer afforded PS graft chains along with exfoliation of each silicate layer to contribute to a uniform dispersion of inorganic nanosheet. The resulting PS-grafted magadiite (PS-g-magadiite) was then mixed with PS homopolymer by a meltblending process, forming PS/magadiite nanocomposites with fine dispersion of magadiite, which was confirmed by X-ray diffraction, transmission electron microscopy and dynamic mechanical analysis. A series of PS/magadiite composites with various dispersion states and blending ratios were molded into pressed-film-type test pieces to evaluate their flammabilities by cone calorimetric measurements. A peak heat release rate (PHRR) of well-dispersed PS/magadiite nanocomposites was half of that of the PS homopolymer. The dispersibility of magadiite was found to be a crucial factor for improving flammabilities for PS/magadiite composites. Polyphenylene ether-PS/magadiite nanocomposites were also prepared in a similar manner using the PS-g-magadiite nanosheet, but they could not suppress higher PHRR.