Hydrolysis-condensation kinetics of 3-(2-amino-ethylamino)propyl-trimethoxysilane

The kinetics of the hydrolysis and self-condensation reactions of 3-(2-amino-ethylamino)propyl-trimethoxysilane (DAMS) were investigated by in situ29Si NMR spectroscopy using pure water and an alcoholic (80:20 w/w ethanol/water) solvent mixture as reaction media. In both media, the reactivity of the silane was strongly influenced by the pH of the medium during the initial stage of the reaction. The silanols produced by hydrolysis in water were much more stable than those produced in the alcoholic solvent mixture, the latter of which were susceptible to self-condensation, yielding siloxane bridges. The active silanol reactivity (SR), which is a simple parameter that reflects the silanol content in the solution as a function of the reaction time, was proposed for evaluating the reactivity of a solution of DAMS. SR was maintained at a good level (high silanol group concentration) when pure water was used as the reaction medium. The pH of the reaction appears to be the predominant parameter for determining the SR during the first 2 h, regardless of the reaction solvent.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► In situ29Si NMR as a tool to study the kinetics of a silane coupling agent. ► The effect of the solvent and the pH were evaluated. ► Equilibrium between hydrolyzed and condensed species in pure aqueous medium. ► The reactivity index of the studied silane in water solutions is very high. ► This silane coupling agent is potentially interesting to graft natural fibres.