Structures of oligomeric silsesquioxanes (POSS)
Polyhedral oligomeric silsesquioxanes (POSS) compounds described by the chemical formula (RSiO3/2)n (where n = 6, 8, 10, 12; R = H, alkyl, aryl), constitute a family of three-dimensional organosilicon compounds containing siloxane Si–O–Si moieties. Such species possess various structures including ladder-like, cage-like, and open-cage motifs. Their molecular structure strictly depends on reaction conditions. Because of the well-defined 3D structure, the most promising seem the cage-like systems. It is possible to obtain these type of compounds with a variety of structural frameworks like hexamers (T6),octamers (T8), decamers (T10), and dodecamers (T12). Their synthesis is challenging and in many cases cumbersome due to the formation of variety of structures derived from different Si–O connections types. Molecular silsesquioxanes are organosilicon are considered as the smallest existing silica nanoparticles, due to their diameters in the range of 1–3 nm. Another advantage of POSS building blocks lies in their high thermal stability and chemical versatility, which means that various R substituents can be covalently attached to the silicon atom.
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