Using a prehydrolysis technique, transparent gels with very high aluminum content can be achieved with the use of isopropanol. Here 13C, 27Al, 29Si and 17O NMR at various stages of preparation show that when the aluminum added exceeds the number that silanols can fully protect, the excess aluminum alkoxide groups readily undergo transesterification with isopropanol. The aluminum isopropoxide (Al-OPri) groups thus formed are shown to be sufficiently stable that attack by water is impeded, thus allowing the remaining silicon alkoxide groups to hydrolyze and condense to form a homogeneous gel.
Bibliographical noteFunding Information:
This work was supported by the Office of Naval Research and by a fellowship to GAP from the University of Minnesota Center for Interfacial Engineering, an NSF Engineering Research Center. The authors are also grateful for helpful discussions with Prof. Christopher Macosko, Dr. Jorge Sanchez (U. of Minnesota), and Dr. Joseph Bailey (3M), and Kangtaek Lee (U. of Minnesota).
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