Postgrafting of hyperbranched dendritic polymer from terminal amino groups of polymer chains grafted onto silica surface

This paper describes postgrafting of hyperbranched dendritic polyamidoamine initiated from terminal amino groups of polymer chains grafted onto ultrafine silica surface in order to modify the silica surface. Surface grafting of polymer having terminal amino groups as initiator sites was performed by a reaction of terminal diamine-type polyoxyethylene with epoxy groups previously introduced onto the surface by 3-glycidoxypropyltrimethoxysilane treatment. The postgrafting reaction of dendritic polyamidoamine from the terminal amino groups was achieved by repeating the Michael addition of methyl acrylate: to amino groups followed by amidation of the resulting ester moieties with ethylenediamine or hexamethylenediamine. Both the amount of amino groups and the percentage of postgrafting of the resulting polyamidoamine increased with an increase in the number of generations: the amino group content increased from 0.40 mmol/g to 2.68 mmol/g, and the percentage of postgrafting reached 61.0% after the 12th generation by using ethylenediamine in amidation. These values, however, were considerably smaller than the theoretical values. This indicates that the postgrafted polyamidoamine was a hyperbranched polymer but not a precise dendrimer. Ethylenediamine as a reactant in amidation was more effective than hexamethylenediamine. and a low content of initial amino groups was also preferred to a large amount of them probably because of steric hindrance in the propagation of hyperbranched dendritic polyamidoamine. The average particle size of hyperbranched dendritic polyamido-amine-postgrafted silica measured by light scattering photometry increased with an increase in the number of generations of the resulting polyamidoamine.