Silica surface modification by cationic polymerization and carbenium intermediates

Modification reactions of bare silica particles with cationically polymerizable monomers are reported. Suitable monomers for silica surface functionalization are p-methoxystyrene, cyclopentadiene, 2-furfuryl alcohol, 2-vinylfurane and 1,3-divinyl-imidazolidin-2-one. It is of importance that the initiating surface group and the propagating chain are mediated on to surface silanol groups by basic counter ions, e.g. chloride, bromide, hydrogen sulfate or trifluoroacetate. A general mechanism of cationic surface polymerization on acidic surfaces is discussed based on model reactions of 1,4-cyclohexadiene upon surface linked carbenium intermediates, electrokinetic measurements, UV/Vis spectroscopy and various MAS NMR spectroscopic methods. The formation of silicon oxygen carbon bonds and their occurrence on the polymer silica interface of the novel solid hybrid materials is investigated by solid state C-13 NMR spectroscopy and DRIFT spectroscopy. The surface properties of silica can be widely controlled by grafting and post functionalization as demonstrated by zetapotential, NMR spectroscopy and XPS measurements. (C) 2000 Elsevier Science Ltd. All rights reserved.