Synthesis and characterization of covalently functionalized laponite clay

Covalently functionalized Laponite clay was synthesized through a condensation reaction of the clay's silanol groups with mono- and trifunctional alkoxy silanes. Most of the work focuses on primary-amine-containing modifications because that group offers a wide range of derivitization options. Various 3-aminopropyltrimethoxy silane (APS) treatments yielded 4-14 wt % of organic material bound to the clay. APS-treated clay was further reacted to yield attached methacrylate, benzophenone, and tertiary bromine groups capable of polymerization, photoinitiation, and atom transfer radical polymerization initiation, respectively. Studies using a monoalkoxy analogue of APS, aminopropyldimethylethoxysilane (APES), are consistent with the hypothesis that multifunctional alkoxy silanes can cause the clay sheets to link together, hindering the clay's dispersibility and the efficiency of subsequent surface ion-exchange reactions. The attached amines were further reacted to 40 and 80% conversion in the APS- and APES-treated Laponites. Quantification studies show that there are about 200 siloxane-reactive sites per clay sheet at a concentration of 11 mequiv per 100 g of clay. All products were characterized with thermogravimetric analysis and solid-state C-13 NMR to study the organic content and composition. Si-29 solid-state NMR was also used to compare the treated clay with untreated sodium Laponite. Changes in the Si-29 spectra were consistent with the expected silanol reaction.