Plane-wave density functional theoretic study of formation of clay-polymernanocomposite materials by self-catalyzed in situ intercalative polymerization

It has recently been shown that the intercalation and subsequent in situ po lymerization of organic monomers within the interlayer of clay minerals yie lds nanocomposites with novel material properties. We present results of pl ane-wave density functional theory (DFT) based investigations into the init ial stages of the polymerization of methanal and ethylenediamine within the interlayer of sodium montmorillonite. Nucleophilic attack of the amine on the aldehyde is only observed when the aldehyde is protonated or coordinate d to a metal ion. No evidence is found for the dissociation of water in the hydration sphere of the sodium counterions. The Bronsted acidity of the hy droxyl groups present in the silicate layers is significantly affected by t heir proximity to sites of isomorphic substitution. However, the most obvio us Bronsted acid sources are shown to be unlikely to catalyze the reaction. Instead catalysis is shown to occur at the clay mineral lattice-edge where hydroxyl groups and exposed aluminum ions act as strong Bronsted and Lewis acid sites, respectively.