Direct synthesis, characterization and solid-state NMR spectroscopy of large-pore vinyl-functionalized cubic mesoporous silica FDU-12

Abstract

Large-pore vinyl-functionalized cubic mesoporous silica FDU-12 materials have been synthesized through the room temperature co-condensation of tetraethoxysilane (TEOS) and trimethoxyvinylsilane (TMVS) under acidic conditions templated with triblock copolymer Pluronic F127. The materials thus obtained were characterized by a variety of techniques including powder X-ray diffraction, multinuclear ( 1H, 13C, 29Si) solid-state NMR, two-dimensional (2D) 13C{ 1H} and 29Si{ 1H} HETCOR NMR, IR, thermogravimetric analysis, and nitrogen sorption measurements. Direct evidence of the presence of chemically attached vinyl moieties was provided by solid-state 1H, 29Si, and 13C NMR. The 2D 13C{ 1H} and 29Si{ 1H} HETCOR NMR experiments correlated the well-known vinyl 13C and 29Si T group resonances with their corresponding 1H NMR peak at 5.8 ppm, respectively. In particular, 29Si{ 1H} HETCOR NMR established that the vinyl groups were cross-linked to the mesoporous silica framework, instead of forming a separate phase. This provides direct molecular-level evidence for the co-condensation of TMVS and TEOS in the synthesis of mesoporous organosilicas. The vinyl functional groups were stable to at least up to 300 °C. The accessibility and the reactivity of the vinyl groups in the mesopores were demonstrated by the formation of a polymer/silica composite through in situ polymerization of vinyl groups with adsorbed methyl methacrylate monomer.