POSS-Based Functional Nanomaterials, Composites, and Additives

Dear Colleagues,

Polyhedral oligomeric silsesquioxanes (POSSs) have been used over the past few decades for a variety of applications, including as functional materials in optoelectronics, lightweight structures, and additive manufacturing. Moreover, among the significant advances made towards their use in fuel cells, optical devices, sensors, optoelectronics, solar energy harvesting, and thermoelectric devices, the POSS family is predicted to have high demand due to their capability in functional tunability via ligand-tailoring chemistry and having rigid and thermally stable silsesquioxane core structure. Thus, these hybrid structures have been incorporated into a variety of materials to enhance their properties, such as thermal stability, optical transparency, toughness, and solubility.

POSSs are specifically classified as cubic T₈ silsesquioxanes, which consist of a rigid, crystalline silica-like core that has a perfectly defined atomic spatiality in the range of 0.5–0.7 nm, and the core is linked covalently to eight R groups. Depending on the number of repetitive units in the general formula (RSiO_1.5)_n (n = 4, 6, 8, and 10–16), there are different types of T_n silsesquioxane structures, which also belong to POSS family. In addition to fully condensed T_n silsesquioxane structures with n = 4, 6, 8, 10, 12, 14, and 16, incompletely condensed structures containing Si–OH groups are known, which have the generic formula [R–SiO_1.5−x(OH)_2x]_n or T_n(OH)_m. Thus, the structures of POSS family include perfect polyhedra, incompletely condensed polyhedra (species with 1–3 OH per molecule), ladder-type structures (species with 4 OH per molecule), open structures (species with more than 5 OH per molecule), linear structures, and all their possible combinations. For example, POSSs with functionalizable sites at silicon vertices wherein the number of reactive sites can be varied from 1 to 8 can yield an entire class of silicon-based organic–inorganic hybrid materials with a POSS incorporated as the central core in dendrimers and hyperbranched polymers, as well as pendants on polymer chains.

The aim of this Special Issue is to highlight the progress on the synthesis, characterization, properties, and applications of functional POSSs and POSS-based composites, additives, and nanomaterials.

Dr. Hemali Rathnayake
Guest Editor

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