Ozin prepared the materials, which they call "periodic mesoporous dendrisilicas," by self-assembly of carbosilane-type dendrimers around a template [Science, 306, 1529 (2004)]. "The main advantage of using carbosilane-type dendrimers as precursors to hybrid mesoporous sieves is that it allows one to control not only the content of the organic functional groups precisely--that is, the silicon-to-carbon ratio--but also the local architecture within the mesoporous walls," comments Andreas Stein, chemistry professor at the University of Minnesota, Twin Cities. "The local connectivity is predesigned into the building blocks and appears to be largely maintained in the templated products." Landskron and Ozin synthesized the building blocks by ethanolysis of Si[(C2H4)SiCl3]4 and related compounds. They then hydrolyzed and condensed the dendrimers around a cylindrical template. "We use ionic surfactants or triblock copolyethers as templates," Landskron explains. "The dendrimers carry a polymerizable triethoxysilyl group. Upon polymerization around the template, an ordered template-polydendrimer nanocomposite is formed." The template is extracted with an organic solvent to give the ordered mesoporous polydendrimer.
by MICHAEL FREEMANTLE |
November 29, 2004