Epoxy self-polymerization in smectite clays

The diglycidyl ether of bisphenol A, epoxy resin Epon-828, undergoes self-polymerization when heated with acidic onium ion exchanged forms of montmorillonite to form polyether-clay nanocomposites. Nanocomposite formation is accomplished by a dramatic transition from a gel state to a dry powder with a very low bulk density. XRD and TEM studies indicated that the final product contains a uniform dispersion of exfoliated 10 Angstrom thick clay plates separated by a few nanometers of polyether polymer, thus verifying the nanocomposite structure. DSC results showed that two exothermic catalytic processes occur during the reaction. The lower temperature process is attributed to polymerization of pre-intercalated epoxide on the internal gallery surfaces where the proton concentration is a maximum. Polymerization of the extragallery monomer on the external and internal surfaces of the day particles occurs at the higher temperature. The acidity of the clay exchange cation plays a major role in catalyzing epoxy self-polymerization, especially the intragallery polymerization process. The activation energies for polymerization of intra- and extragallery monomer, as determined by DSC measurements, are 84 and 130 KJmol(-1), respectively.