Preparation and properties of hyperbranched poly(amidoamine) grafted onto a colloidal silica surface

Grafting of hyperbranched poly(amidoamine) (PAMAM) onto a colloidal silica surface was achieved in a solvent-free dry system and in a methanol solvent system using dendrimer synthesis methodology. The hyperbranched PAMAM was grown from amino groups on the colloidal silica surface by repetition of two steps: (1) Michael addition of methyl acrylate (MA) to amino groups on the surface and (2) amidation of the resulting terminal ester groups with ethylenediamine (EDA). The extent of PAMAM grafting in the solvent-free system and in the methanol solvent system were determined to be 60.4 and 62.8%, respectively. However, both of these values were considerably smaller than the previously calculated theoretical values. This indicates that propagation of PAMAM from the colloidal silica surface did not take place in the manner theoretically predicted; instead, due to steric hindrance, the polymer was grafted in hyperbranched fashion. The terminal amino groups of hyperbranched PAMAM-grafted silica were found to be effective in curing epoxy resin. The gel fraction of the cured resin increased as the proportion of PAMAM on the silica surface increased. Vinyl polymers were postgrafted to the terminal groups of the hyperbranched grafted PAMAM by radical polymerization, which was initiated by a system consisting of hyperbranched PAMAM-grafted silica with terminal trichloroacetyl groups (Silica–PAMAM–COCCl3) and Mo(CO)6.