Covalent attachment of poly(allylamine hydrochloride) onto ordered silica foams

In this work, a new approach for the modification of mesocellular silica foam (MCF) with poly(allylamine hydrochloride) (PAH) through free radical polymerization of the respective monomer is reported. The modification route involved the functionalization of MCF with vinyltrimethoxysilane as first step followed by the free radical copolymerization of the grafted organosilane-coupling agent with the monomer allylamine hydrochloride (AA⋅HCl). As far as we know, this is the first report about the covalent modification of ordered-mesostructure silica with PAH by free radical polymerization of AA⋅HCl. Several parameters of polymerization reaction such as initiator and monomer concentrations, and reaction time were varied in order to tune the content of PAH in the obtained hybrid material MCF–PAH. Grafting was corroborated by infrared spectroscopy and X-ray photoelectron spectroscopy while the polymer content was determined by thermogravimetric analysis. The polymer content could be tuned from 12 to 42% without modification in the MCF structure as confirmed by small angle X-ray scattering, scanning electron microscopy, and transmission electron microscopy. Textural properties of MCF such as pore volume and BET surface decreased as the PAH content increased which confirmed the grafting of this polymer onto silica. The resulting silica composites could find application as gas adsorbents, drug delivery systems, and recovery of heavy metals from wastewater.