Silsesquioxane - Background

Background

Since their initial discovery, silsesquioxanes have been a frequent and productive topic of research that has become interwoven into many fields of science, including energy, materials, catalysis and bioengineering. The extent of this variation is largely due to the molecules themselves, which have been found to form a number of different structure types. Though the basic formula for all silsesquioxanes has been found to be RSiO_3/2 with the identity of R typically being alkyl or organo-functional groups, the combined structure of these RSiO_3/2 units vary depending on synthesis methods, starting materials and the catalyst used. The four most common silsesquioxane structures are cage structures in which the units form a cage of n units in a designated T_n cage, partial cage structures, seen in Figure 2, in which the aforementioned cages are formed but lack complete connection of all units in the cage, ladder structures in which two long chains composed of RSiO_3/2 units are connected at regular intervals by Si-O-Si bonds, and finally random structures which include RSiO_3/2 unit connections without any organized structure formation.

The high three dimensional symmetry and nanometer size makes silsesquioxanes very useful building blocks for nanocomposites. The diversity of possible functional groups along with their controlled orientation in 3-D space allows for highly tailored nanometer-by-nanometer construction in all three dimensions with these unique nanobuilding blocks. The silica core gives rigidity and thermal stability that provides mechanical and thermal properties surpassing typical organics. Combining the robust core with the functionalities of the attached organic groups can also change the physical properties of the SQs allowing for easier processing than typical ceramics. The mixture of organic and inorganic functionalities can lead to the creation of novel nanocomposite materials that exhibit properties intermediate and superior to those of traditional polymer and ceramic properties. Tailored SQs provide a solution where processing conditions prevent ceramic-like materials from being plausible or mechanical requirements prevent polymer-like materials from being useful. The significance of SQs can be seen from their vast application possibilities in diverse fields including aerospace, antimicrobials, photonics, microelectronics, semiconductors, cosmetics and catalysis science.