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Bridged
Polysilsesquioxanes: Porous Materials
 
Bridged polysilsesquioxane gels can
be air dried or crushed, washed and oven dried to afford xerogels or supercritcally
extracted with carbon dioxide to give aerogels. Xerogels under significant
shrinkage during drying-losing up to 95% of their volume. However, despite
these losses in volume many bridged polysilsesquioxane xerogels routinely
have surface areas in excess of 1000 m2/g and pore volumes greater than
1 mL/gram. The nature of the bridging group can have remarkable effects
on the pore size distributions. Rigid groups such as arylenes give rise
to mostly microporous xerogels. Flexible spacers such as long, linear alkylenes
give rise to nonporous or mesoporous xerogels-depending on if the polymerizations
were carried out under acid or basic conditions, respectively. We have also
shown that the average pore size can be controlled by the nature of the
bridging group with monomodal pore size distributions rivaling those of
templated amorphous or microcrystallline zeolites. Bridged polysilsesquioxane
aerogels retain much more of their original gel volume and have significantly
higher surface areas (up to 1850 m2/g) and larger pore sizes. Efforts are
underway to capitalize on these extraordinarily high surface areas and the
high degree of chemical functionality for membranes, sorbents, chromatographic
stationary phases, and catalyst supports.
Small, James H.; Shea, Kenneth J.; Loy,
Douglas A. Arylene- and Alkylene-Bridged Polysilsesquioxanes. J.
Non-Cryst. Solids (1993), 160(3), 234-46.
Contact: Doug Loy
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