Intercalation of polymerization initiators into montmorillonite nanoparticle platelets: free radical vs. anionic initiator clays

We have investigated the properties of clay surface bound initiators for the preparation of polymer-layered silicate nanocomposite materials: one for anionic and two for free radical polymerization. These organic cations were intercalated into the galleries of montmorillonite clay by cation exchange. The structural, thermal, and compositional properties of the three types of initiator clays were studied and compared. X-ray diffraction studies showed that all three systems were swelled after initiator intercalation and the increase of interlayer d-spacing was dependent on the structure and molecular chain length of the initiators. Thermal gravimetric analysis, differential scanning calorimetry, and X-ray photoelectron spectroscopy traces indicated the presence of the initiator on clay and a complete cation exchange process was achieved only by adding excessive amounts of initiator. Infrared spectra compositionally confirmed the successful initiator intercalation into the clay platelets. Important differences were found between surface bound mono and dicationic free radical initiators.