Silsesquioxane (POSS)

Silsesquioxane (POSS) List

The general formula of cage silsesquioxane, POSS, for short, is (RSiO1.5) n, in which R is the group connected by eight vertex Si atoms, usually hydrogen, alkyl, aryl, alkenyl, halogen and so on. POSS has a clear three-dimensional structure, and its organic and inorganic groups are combined by the covalent bond. Therefore, POSS has the characteristics of inorganic/organic compounds and has good compatibility with organic polymers, so it can be used to construct polymer / POSS nanocomposites. Besides, the organic groups connected to Si atoms can be derivatized to prepare new POSS with different structures. Some POSS with active functional groups can be copolymerized with polymer monomers to prepare nanocomposites with excellent properties.

Figure 1. Three-dimensional structure of POSS.

Applications:

• Optical materials: Much attention has been paid to the application of POSS in optical materials, especially in luminescent materials. Fluorescent POSS can be prepared by introducing fluorescent dyes or active metal ions (lanthanide) into the preparation of POSS. The preparation method is simple, the product is easy to separate, the fluorescence intensity is high, the light resistance and chemical resistance are strong. The fluorescent material can be used in bioanalysis, biomedical materials, especially cell labeling in vivo. In addition, fluorescent POSS materials with functional biomolecules (such as proteins, enzyme molecules, peptides, and DNA) are expected to be used in high-throughput detection, imaging systems, and drug delivery systems.

Figure 2. Synthesis of POSS fluorescent microspheres.

• Biomedical carrier materials: How to improve the therapeutic effect of radiotherapy and chemotherapy, photodynamic therapy and the signal contrast and diagnostic sensitivity of contrast agents used in magnetic resonance imaging (MRI) are the focus of oncology. POSS has become a new generation carrier of anticancer drugs, photosensitive agents and contrast agents because of its surface effect, quantum confinement effect and specific functional groups. For example, cisdichlorodiammine platinum (cisplatin) was loaded into POSS and then modified with polyethylene glycol to improve biocompatibility. The prepared PEG-cisplatin-POSS nanospheres can be used in drug release and anti-tumor therapy.
• Flame retardant material: POSS has good thermal and chemical stability and can be used as a high-temperature resistant material, especially polysesquisiloxane (PPSQ), with high charring benzene ring is an excellent flame-retardant material. Some researchers modified PPSQ to improve the adhesion, mechanical properties and thermal stability of flame retardant materials, to prepare polyvinyl phenol silsesquioxane microspheres and poly epoxy phenyl siloxane microspheres with good flame retardancy.
• Other applications: POSS also has potential applications in functional hybrid coatings, adsorption, chromatographic analysis and electrochromic materials. Studies have shown that POSS is a kind of solid amine carbon dioxide adsorption material with excellent adsorption performance and renewable. In addition, PMSQ, PVSQ and PMPSQ MPs were used in the superhydrophobic treatment of cotton fabrics (adding isocyanate cross-linking agent). The results show that the cotton fabrics treated with PMSQ and PVSQ with hydrophobic groups have durable super-hydrophobic properties. In addition, metal hybrid POSS (such as POSS-Au and POSS-Pd) can also be used in templates, reducing agents and ligands.

References

1. Chunxin Zhang, Florence Babonneau. (1998) “Highly Porous Polyhedral Silsesquioxane Polymers. Synthesis and Characterization.” J. Am. Chem. Soc. 120 (33), 8380-8391
2. Hao Lifen, Yang Ruini.(2017) “Progress in synthesis and application of polysilsesquioxane micro/nanospheres.” FINE CHEMICALS. 34 (1), 5214-5224