Alkoxysilylated-derivatives of double-four-ring silicate as novel building blocks of silica-based materials

Novel oligomeric alkoxysilanes consisting of double-four-ring (D4R) units functionalized with mono-, di-, and trialkoxysilyl groups (designated as 1, 2, and 3, respectively) were designed as nanobuilding blocks for synthesizing silica-based nanomaterials. Hydrolysis and polycondensation of these oligomers were performed under acidic conditions. The gelation occurred much faster than monomeric, dimeric, and cubic octameric alkoxysilanes, which should depend on both molecular size and siloxane structures. Structural analyses of the xerogels derived from 1-3 strongly suggested that the D4R units are at least partly retained in their frameworks. The number of alkoxy groups had a large effect on their porosities: the xerogel derived from 2 was a microporous solid with the BET surface area of 600 m² g^-1, whereas 1- and 3-derived xerogels had very low BET surface areas. Furthermore, mesostructured silica films were successfully synthesized from 2 and 3 by using amphiphilic triblock copolymer surfactant as a structure-directing agent. Such an approach will lead to the construction of molecularly designed siloxane networks.