Preparation, characterization and properties of polymer-layered silicate nanocomposites

This study focused on the synthesis and characterization of polymer-layered silicate nanocomposites. A polycarbonate-layered silicate nanocomposite was prepared by in-situ ring opening polymerization. Poly(methyl methacrylate)-layered silicate nanocomposites were prepared by both in-situ suspension polymerization and emulsion polymerization.; A partly exfoliated bisphenol A polycarbonate nanocomposite was prepared using carbonate cyclic oligomers and ditallow dimethyl ammonium exchanged montmorillonite. Wide angle X-ray diffraction (WARD) indicated that exfoliation of this organically modified layered silicate occurs after mixing with the cyclic oligomers in a Brabender mixer for 1 hour at 180°C. Subsequent ring-opening polymerization of the cyclic oligomers converted the matrix into linear polymer without disruption of the layer dispersion. Transmission electron microscopy (TEM) revealed that a partially exfoliated structure was obtained, although no indication of layer correlation was observed in WAXD. Melt intercalation of polycarbonate gave intercalated nanocomposites.; Poly(methyl methacrylate) (PMMA) nanocomposites were prepared by in-situ suspension polymerization and emulsion polymerization. In the suspension polymerization method, a modified layered silicate was used as suspension stabilizer. Different modified layered silicates produced different structures (intercalated or exfoliated). In the emulsion polymerization method, PMMA polymers were first prepared by emulsion polymerization without silicate present. Then the polymer emulsion and an aqueous dispersion of inorganic layered silicate were mixed and the nanocomposites precipitated. Structures of the nanocomposites were controlled by using different surfactants in the emulsion polymerization step. WAXD, TEM and atomic force microscopy (AFM) were used to characterize the structure of the nanocomposites. These polymer-layered silicate nanocomposites demonstrated improved thermal stability when compared to pure polymer.