Octaphenyl Silsesquioxane Polyhedral Oligomeric Silsesquioxanes (POSS) nanostructures have diameters in the range 1–3 nm and, hence, may be considered as the smallest existing silica particles. POSS particles have been classified as having a zero-dimensional, however the ability to create higher dimensional POSS (1, 2 or 3-D scaffolds) through aggregation or crystallization of the these particles within the polymer matrix has also been reported. This ability of POSS to serve as building blocks plays a key role in motivating the study of POSS in polymer matrices.

Octaphenyl Silsesquioxane POSS-containing polymer composites depend on the successful incorporation of POSS particles in polymeric matrices. Two approaches have been adopted to incorporate POSS particles into polymer matrices: (i) chemical cross-linking and (ii) physical blending. In the first approach, POSS nanoparticles are bonded covalently with polymer and in the second approach, they are physically blended with polymer by melt mixing or solvent casting methods.

Octaphenyl Silsesquioxane POSS are nanostructures with the empirical formula RSiO_1.5, where R may be a hydrogen atom or an organic functional group, e.g., alkyl, alkylene, acrylate, hydroxyl or epoxide unit. POSS may be referred to as a silica nanoparticles consisting of a silica cage core, as well as other organic functional groups attached to the corners of the cage. POSS consists of both organic and inorganic matter with an inner core of inorganic silicon and oxygen and an outer layer of organic constituents, which could be either polar or non polar.

Octaphenyl Silsesquioxane POSS nanoparticles embedded into a polymer increase the strength, modulus, rigidity and reduce the flammability, heat discharge and viscosity of the polymer, while retaining its light weight and ductile features. These enhanced properties allow for a wider range of applications of these nanocomposites, e.g., drug delivery, polymer electrolytes, thermoplastic and thermosetting polymers. Other benefits to POSS include being non-volatile, odorless and overall environmentally friendly. In addition, the ease with which they can be synthesized makes them commercially available. Considering these potential commercial uses and their increased performance over their non-hybrid counterparts, POSS-containing polymer nanocomposites have been widely investigated.

Octaphenyl Silsesquioxane POSS combines the rigid cage of C60 with the high functionality of hyper branched polymers .This has helped POSS find some applications. For example in Colorless Polyimide; Polyimide is a transparent, high temperature polymer with a characteristic orange tint. A copolymer of fluoropolyimide and POSS gives a colorless material with increased resistance to etch from atomic oxygen in Low Earth Orbit (important for satellites) or from oxygen plasma. When exposed to strongly oxidizing conditions, the POSS vitrifies to make a protective glassy layer.