Highly functionalized bridged silsesquioxanes |
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Authors: | Zhou Guannan Simerly Thomas Golovko Leonid Tychinin Igor Trachevsky Vladimir Gomza Yury Vasiliev Aleksey |
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Institution: | (1) Department of Chemistry, East Tennessee State University, PO Box 70695, Johnson City, TN 37614, USA;(2) Institute of Bioorganic Chemistry and Petrochemistry, NAS of Ukraine, 1 Murmanska St., 02094 Kiev, Ukraine;(3) Technical Centre, NAS of Ukraine, 13 Pokrovska St., 04070 Kiev, Ukraine;(4) Institute of Macromolecular Chemistry, NAS of Ukraine, 48 Kharkivske Shosse, 02150 Kiev, Ukraine; |
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Abstract: | The objective of this work was to synthesize functionalized mesoporous silsesquioxanes with high concentrations of amine groups.
During typical sol–gel syntheses, these materials are obtained by co-condensation of organic precursors with suitable linkers,
such as tetraethoxysilane, necessary to prevent the mesoporous structure from collapsing. Thus, concentrations of amine groups
in organosilicas usually do not exceed 2.7–3.4 mmol g−1. The use of bridged bis-trimethoxysilanes, however, allowed formation of mesoporous materials with no linker. Polycondensation of bis-trimethoxysilanes containing amine groups was conducted in acidic, neutral and basic media, resulting in high yields of solid
bridged silsesquioxanes. Gelation occurred quickly if no acid or base was added to the reaction mixture. The hybrid organic/inorganic
nature of obtained materials was confirmed by FT-IR and MAS CP NMR spectroscopy. Elemental analysis showed that amino group
concentration in the products was 3.3–4.1 mmol g−1. Measurement of particle size distribution confirmed that choice of reaction media significantly affects particle sizes and
agglomeration degrees, with the largest agglomerates (up to 50 μm) formed in basic media. A morphology study, using small-angle
X-Ray scattering, displayed two-level fractal structures composed of aggregated 6.5–10.5 nm particles. Reactions in the presence
of a surfactant resulted in formation of mesoporous structures. Furthermore, the obtained bridged silsesquioxanes were thermally
stable down to 260 °C, but could reversibly absorb water and CO2 at temperatures below 120 °C. Thus, condensation of the bridged precursor without a linker resulted in formation of a highly
functionalized mesoporous material. |
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