Periodic Mesoporous Organosilicas with Phenylene Bridging Groups, 1,4-(CH₂)nC₆H₄ (n = 0−2)

Periodic mesoporous organosilicas (PMOs) were prepared by polymerizing phenylene-bridged silsesquioxane precursors containing an incremental increase in methylene spacers [1,4-(CH 2 ) n C 6 H 4 ( n = 0−2)] in combination with polyoxyethylene(10) cetyl ether (Brij 56) oligomers as structure-directing species under acid catalysis. Surfactant templates were removed from the nanoporous inorganic−organic hybrids using acidified ethanol extractions. Mesoporous organosilicas were characterized by powder X-ray diffraction, nitrogen gas sorption, 13 C and 29 Si solid-state NMR, scanning and transmission electron microscopy, and thermogravimetric analysis. Organosilica materials formed uniform arrays of 2D-hexagonal mesopores with pore diameters ranging from 2 to 3 nm and corresponding surface areas of 750−1200 m 2 g - 1 . Addition of two methylene groups to the phenylene bridge resulted in a substantial decrease in the pore size, surface area, and pore volume. The thermal stability of the materials decreases in the following order: phenylene > 4-benzyl > p -xylene. Aryl−silicon bonded networks display greater thermal stability than methylene−silica covalently bound frameworks. Decomposition of aryl−silica units occurred between 450 and 750 °C, whereas methylene−silica moieties decomposed in the range 300−600 °C. These hybrid mesoporous materials represent the first introduction of precursors with two-structural organic-bridging units as an integral part of the organosilicate-bonded matrix.