Investigation and Preparation of Hydrolytically Stable Aminosilane-derived Layers on Silica Surfaces
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Aminosilanes are commonly used to functionalize silica substrates. The hydrolytic stability of aminosilane-derived layers is a major consideration in choosing suitable reagents for aqueous applications. We recently reported that aminosilane-derived layers prepared with the most widely used silane coupling agents, 3-aminopropylalkoxysilanes, suffer extensive loss upon exposure to water at moderate temperatures. This is likely caused by siloxane bond hydrolysis catalyzed by the amine functionality via the formation of a stable five-membered intermediate. In this study, we evaluated the performances of five silane coupling agents, 3-aminopropyltriethoxysilane (APTES), 3-aminopropyltrimethoxysilane (APTMS), N-(6-aminohexyl)aminomethyltriethoxysilane (AHAMTES), N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AEAPTES), and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPTMS). They have the general structures of NH2(CH2)kSi(OR)3 and NH2(CH2)nNH(CH2)mSi(OR)3 , where R represents either a methyl or an ethyl group. Silanization was carried out on silicon wafers in anhydrous toluene or in the vapor phase. The hydrolytic stability of aminosilane-derived layers was correlated with the reaction conditions and the silane structural features.