Solid-state NMR evaluation of the silane structure on nanoporous silica fillers

Abstract

Coupling agents play a critical role in the function of organic/inorganic composite materials. However, the structure of these compounds as they reside on the filler surface is not well understood. Solid-state CP-MAS T13C and 29Si FT-NMR were used to study the coupling of γ-methacryloxypropyltrimethoxysilane (MPS) on experimental nanoporous silica fillers following exposure to different coupling environments. The progressive consumption of Si OH species by the coupling reaction was clearly detected. Ethanol, a widely utilized solvent in coupling reactions, competes with the coupling agent for the surface. Different degrees of coupling apparently produce surface structures that vary from isolated MPS molecules to heavily condensed films. The use of CP-MAS 13C-NMR presents some advantages, as it detects uncondensed MPS molecules in the most condensed film. These results show that NMR can provide information that is otherwise unavailable on the attachment and structure of silane coupling agents resident on the surface of porous silica fillers.