Polyhedral Oligomeric Silsesquioxane (POSS) Chemistry

Epoxy nanocomposite vitrimers containing polyhedral oligomeric silsesquioxane (POSS) were reported by Hongkun Yang, Changfei He, Thomas P. Russell, and Dong Wang in Giant in 2020. Studies devoted specifically to POSS in vitrimer networks remain scarce, and this one still carries the subject almost on its own. Glycidyl POSS was incorporated as a nanoscale filler into a transesterification-based epoxy, raising tensile strength and strain at break simultaneously while shifting the topology-freezing transition upward by more than 36 °C. A handful of related reports place silsesquioxane particles in other dynamic matrices, among them the bio-based polymethacrylate vitrimer nanocomposites of Hajiali, Tajbakhsh, and Marić, and in every case the cage serves as reinforcing filler. Key findings at a glance 10 wt% glycidyl POSS raises the ultimate tensile strength of a transesterification epoxy vitrimer from 21.9 to 35.8 MPa (+63.5%) and the strain at break from 190 to 334% (+75.8%). The topolog...

中文版本 / Chinese version: POSS 八亚胺倍半硅氧烷：晶体结构与热性能 Four novel octa-imine-functionalized polyhedral oligomeric silsesquioxane (POSS) derivatives, designated POSS-6 through POSS-9 , have been reported by Mateusz Janeta and Sławomir Szafert in the Journal of Molecular Structure in 2025. These compounds were obtained by modular Schiff base condensation of octa(3-aminopropyl)silsesquioxane hydrochloride with the appropriate aromatic aldehyde in isolated yields ranging from 84 to 92 percent without chromatographic purification, and their structures were fully established by single-crystal X-ray diffraction. The identity of the peripheral substituent (hydroxyphenyl, bromophenyl, thiophene, or dibenzofuran) was found to govern both the non-covalent interaction topology in the solid state and the thermal behavior, with T 5% decomposition onset temperatures spanning from 305 to 326 °C across the four derivatives.

Among the large and structurally diverse family of polyhedral oligomeric silsesquioxanes (POSS) , octamethylsilsesquioxane — formally designated Si 8 O 12 (CH 3 ) 8 and commonly abbreviated as T 8 -Me or OMS — occupies a unique position as the structurally simplest and historically most studied member of the cubic T 8 series. Its eight methyl groups, one attached to each silicon vertex of the Si 8 O 12 cage, make it the prototype for understanding the geometry, dynamics, spectroscopy, and reactivity of the entire POSS family. Despite its apparent simplicity, T 8 -Me continues to attract sustained scientific interest across disciplines as diverse as materials science, polymer chemistry, computational chemistry, and ceramic engineering.

Bromination of the phenyl rings of octaphenyloctasilsesquioxane proceeds in the ortho position without any Lewis acid catalyst, in contradiction to the regiochemical rules that govern isolated aromatic substrates. The study titled “Why Do the [PhSiO 1.5 ] 8,10,12 Cages Self-Brominate Primarily in the Ortho Position? Modeling Reveals a Strong Cage Influence on the Mechanism” by M. Bahrami, H. Hashemi, X. Ma, J. Kieffer, and R. M. Laine, published in Physical Chemistry Chemical Physics in 2014, accounts for this outcome. The modeling places the bromine molecule 2.7 Å above a cage face, tilted by 30°, with a Br−Br separation of 2.32 Å and an induced dipole moment of 0.33 D, an arrangement that delivers Br δ+ to the ortho carbon. The premise of the present entry, namely that the Si 8 O 12 framework acts as an electron withdrawing center that stabilizes anionic guests and polarizes neutral molecules approaching its faces, is treated in full in the companion entry on the electronic p...

Octavinyloctasilsesquioxane is among the most versatile and widely studied polyhedral oligomeric silsesquioxane (POSS) platforms in hybrid materials chemistry. Its eight peripheral vinyl groups, arranged symmetrically about the cubic silsesquioxane core, consistent with the T8 cage classification , provide an exceptionally rich surface for chemical functionalization through reactions characteristic of terminal alkenes, enabling the rational synthesis of dendrimers, polymer networks, glycoclusters, and metal-coordinating ligands. This article reviews how octavinyloctasilsesquioxane (octavinyl POSS, OVS) is prepared and surveys the principal routes to its derivatives — thiol-ene and radical phosphine addition, epoxidation, platinum-catalysed hydrosilylation, palladium-catalysed Heck coupling and ruthenium-catalysed olefin metathesis — together with the architectures each of them delivers.

HOMO-LUMO Gap and Insulating Character of the Silsesquioxane Core Quantum-mechanical calculations performed for octahydrooctasilsesquioxane showed that the highest occupied molecular orbital (HOMO) of this compound is composed of atomic orbitals associated with the lone pairs of the oxygen atoms, whereas the lowest unoccupied molecular orbital (LUMO) is spherical and is located at the center of the silsesquioxane core, as shown in the figure below. The calculations further indicated that the energy gap between the HOMO and the LUMO amounts to approximately 6 to 7 eV. This value exceeds the 3 eV threshold for conductivity, which confirms that the silsesquioxane core behaves as an insulator.

Wacker-Chemie Patent Origins and the Absence of Early Characterization Data Octa(3-aminopropyl)silsesquioxane salts constitute the practical entry point to polyhedral oligomeric silsesquioxanes (POSS) bearing nitrogen in the organic arms. A one step hydrolytic condensation of (3-aminopropyl)triethoxysilane that affords the chloride, trifluoroacetate and triflate salts in high yield, together with their subsequent conversion into amide derivatives by means of acyl chlorides, has established these compounds as readily accessible building blocks. 1 The history of the parent compound is nevertheless considerably longer. Octa(3-aminopropyl)silsesquioxane hydrochloride (OAS) was first described in a patent filed by Wacker-Chemie GmbH, 2 although that document reports neither a method for its preparation nor the spectroscopic data required for its full identification. 3

Hydrolytic condensation of organotrichlorosilanes remains the workhorse preparation of octameric polyhedral oligomeric silsesquioxanes (POSS). This entry treats that single route in detail, covering the hydrolysis and condensation sequence, the steric control that favors the T 8 cage, and the practical influence of solvent, acidity and reaction time. A comparison of this route with the two remaining synthetic strategies is given on the dedicated overview page linked below. This entry is a focused companion to the main reference page Synthetic Routes to Octameric POSS , which surveys all three principal categories of cage synthesis, including corner capping of incompletely condensed precursors and post synthetic modification of preformed cages. Figure 1. Hydrolysis of an organotrifunctional silane and subsequent polycondensation of the resulting silanols to the octameric T 8 framework.

Silsesquioxane nomenclature governs how chemists name and communicate the structures of polyhedral oligomeric silsesquioxane (POSS) compounds and related organosilicon frameworks. The term silsesquioxane derives from the Latin silicium (silicon), sesqui (one and a half), and oxygenium (oxygen), reflecting the characteristic oxygen-to-silicon atomic ratio of 1.5. Because systematic IUPAC designations for polyhedral silsesquioxanes are unwieldy — reaching 40 or more characters for even the simplest T 8 cage — the field relies on the concise M, D, T, and Q silicon atom classification and on the compact R n T n shorthand notation.

Polyhedral oligomeric silsesquioxane (POSS) chemistry, based on compounds of the general formula RSiO 1.5 , was established in 1946 when D. W. Scott reported the first synthesis of octamethylsilsesquioxane (Me 8 T 8 ) during the thermal rearrangement of branched-chain methylpolysiloxanes. A. Barry subsequently confirmed the crystallinity and oligomeric nature of these compounds in 1955 through powder X-ray diffraction and cryoscopic molar mass determination. J. Brown then extended this work by isolating discrete polyhedral cage compounds containing 8, 10, and 12 silicon atoms, designated T 8 , T 10 , and T 12 , demonstrating that the rigid Si 8 O 12 inorganic core combined with peripheral organic substituents confers both exceptional thermal resistance and broad compatibility with organic polymer matrices. Later developments, from cage functionalization to catalysis and functional materials, are summarized in POSS Silsesquioxane Chemistry: Synthesis to Applications .