Polyhedral oligomeric silsesquioxanes constitute a group of organosilicon compounds with a general formula (RSiO3/2)8 which – from chemical point of view – locate between ceramics and organic materials. The presence of Si-O bonds in the central core of POSS imparts superior thermal, mechanical, and chemical stability, which makes these compounds extremely interesting from an industrial point of view.

Their attractiveness is due to the fact that various R substituents can be effectively anchored to the silicon atom (Figure 1). Covalently bonded organic arms make reactive functionalities suitable for polymerization or grafting. That makes silsesquioxanes unusual because they establish an inorganic silicate core and an organic outer sphere. Such a structure can simply affect rigidity, thermal stability, hydrophobicity, and other remarkable properties. Within the class of cage-like organosilicons such as T6, T8, T10, and T12 considerable attention is focused on T8 cages, which are the most widely studied. Silsesquioxanes nanostructures have diameters in the range of 1–3 nm and, hence, may be considered as the smallest existing silica particles. Silsesquioxanes particles have been classified as having a zero-dimensionality; however, they have the ability to create higher dimensionalities (1, 2 or 3D building blocks) through the functionality of side chains.

Figure 1. Types of octameric (T8) POSS.

Functionalized silsesquioxanes with attractive properties are successfully used in various areas of chemistry, and many interesting examples that illustrate them have already been described. For example, systems based on cage-like silsesquioxanes have been intensively examined in photonics and electronic devices. Phthalimide and o-sulfobenzimide-functionalized silsesquioxanes have been found to be promising materials for the further functionalization of other nitrogen-based silsesquioxanes. Tetraphenyl silsesquioxanes based on covalent-organic frameworks are reported to be efficient hydrogen storage materials. Shape and confinement effects on the supramolecular interactions of hydrogen-bonded bent-core liquid crystals based, inter alia, on silsesquioxanes systems have also been studied for various terminal siloxane groups. The above-discussed materials constitute only a handful of examples of their potential applications in chemistry and industry.