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-(CH2)nC6H4 (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, 13C and 29Si 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 m2g-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.