Synthesis of exfoliated polystyrene/montmorillonite nanocomposite by emulsion polymerization using a zwitterion as the clay modifier

Montmorillonite (MMT) was modified with zwitterion aminoundecanoic acid (AUA). First AUA was protonized to facilitate molecules to get into the galleries of the montmorillonite to accomplish ion exchange, and the carboxyl groups were then ionized in the alkaline aqueous media to enable exfoliation of the clay. It was demonstrated by rheological measurements and atomic force microscopic studies that exfoliation of the clay driven by the electrostatic repulsion took place in an alkaline medium. Polystyrene/montmorillonite (PS/MMT) nanocomposite was synthesized via emulsion polymerization in the presence of the modified MMT. The exfoliated microstructure of the composites was studied by the X-ray diffraction and transmission electron microscopy. The exfoliated PS/MMT nanocomposite showed a greatly improved modulus, a higher glass transition temperature and a better thermal stability compared to the neat polystyrene and the intercalated PS/MMT composites.