Grafting of water-soluble sulfonated monomers onto functionalized fumed silica nanoparticles via surface-initiated redox polymerization in aqueous medium

Abstract

Sulfonated polymer/fumed silica hybrid nanoparticles were prepared via surface-initiated free radical polymerization of 2-acrylamido-2-methyl-1-propane sulfonic acid (PAMPS-g-FSN), styrene sulfonic acid sodium salt (PSSA-g-FSN) and vinyl sulfonic acid sodium salt (PVSA-g-FSN) from the surface of aminopropyl-functionalized fumed silica nanoparticles (AFSNs) dispersed in aqueous medium. Cerium(IV) ammonium nitrate/nitric acid and sodium dodecyl sulfate were used as redox initiator and stabilizer respectively. AFSNs were prepared by covalently attaching 3-aminopropyltriethoxysilane onto the surface of fumed silica nanoparticles. Sulfonated monomers (AMPS, SSA or VSA) were then grafted onto the AFSNs ultrasonically dispersed in water via redox initiation at 40 °C. Structure, thermal properties, particle size and morphology of the AFSNs and PAMPS-g-FSN, PSSA-g-FSN and PVSA-g-FSN hybrid nanoparticles were characterized by Fourier transform infrared spectroscopy, TGA, SEM, transmission electron microscopy (TEM) and dynamic light scattering (DLS). The results indicated that the sulfonated monomers were successfully grafted onto the fumed silica nanoparticles. Grafting amounts of the sulfonated polymers onto the fumed silica nanoparticle surface were estimated from TGA thermograms to be 59%, 13% and 29% for the PAMPS, PSSA and PVSA, respectively. From SEM, TEM and DLS analysis, polymer-grafted fumed silica nanoparticles with an average diameter smaller than 70 nm and a (semi-) spherical shape were observed. A significant bimodal particle size distribution was observed only for the PAMPS-g-FSN with average diameters of 39.6 nm (84.1% per number) and 106 nm (15.9% per number). The hydrophilic sulfonated polymer/grafted fumed silica obtained from the redox graft polymerization gave a stable colloidal dispersion in acidic aqueous medium. © 2012 Society of Chemical Industry.