Macromolecular Templating Approach for the Synthesis of Hydrothermally Stable Mesoporous Organosilicas with High Periodicity and Thick Framework Walls

Hydrothermally stable mesoporous ethanesilica with a long-range hexagonal order (p6mm) and a relatively thick and micropore-free framework wall was synthesized by the core-shell approach using a nonionic PEO-PLGA-PEO triblock copolymer template and a 1,2-bis(triethoxysilyl)ethane (BTESE) organosilica precursor. The pore structure and morphology were characterized by SAXS, TEM, BET, and solid-state NMR measurement. The key parameters in the synthesis of mesoporous ethanesilica with a stable thick wall are the strong contrast between the hydrophilic PEO block and the hydrophobic PLGA block and the compatibility of PEO with the BTESE organosilicate precursor at an optimum reaction temperature of 323 K. The enhanced hydrothermal stability (i.e., the structural integrity was maintained for up to 25 days in boiling water of 373 K) is believed to be due to the thick pore wall (4.2 nm), the high degree of condensation and hydrophobicity of organosilica precursor used, and the significant reduction of micropores.