New Strategy for Functionalization of Silica Materials via Catalytic Oxa-Michael Reaction of Surface Silanol Groups with Vinyl Sulfones

This article demonstrates the catalytic oxa-Michael reaction of inorganic silanol groups with vinyl sulfones, which facilitates an efficient strategy for functionalization of the silica surface. The strategy was applied on materials ranging from nanoscale to macroscale silica, and the surface functionalization was achieved in hours using organo-catalysts at mild temperature. The formation of Si-O-C bonds on the surface was characterized by solid-state C-13 cross polarization magic angle spinning nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Our strategy showed several advantages over traditional methods, and the resulting Si-O-C bond exhibited distinct behaviors toward different solvents. Organic solvents would stabilize the functionalized silica materials, while aqueous solutions would result in degradation affected by both solution and surface factors. With use of divinyl sulfone as a cross-linker, a variety of molecules can be immobilized and sequentially released in a controllable manner, which would benefit a broad range of applications from sensing to drug and catalyst carriers.