Structure Of Polyhedral Oligomeric Silsesquioxane Research Articles

Thermal Insulating and Mechanically Strong Polyimide Aerogel Composites Reinforced by Polyhedral Oligomeric Silsesquioxane-Grafted Carbon Nanotubes

In the ship industry, developing thermal insulation materials with exceptional high-temperature resistance, structural stability and light weight is essential. Herein, polyimide (PI) composite aerogels were synthesized. Carbon nanotubes (CNTs) introduced cross-linking structures within the aerogel matrix, effectively reducing shrinkage and forming micrometer-scale pores. Furthermore, the rigid cage-like structure of polyhedral oligomeric silsesquioxane (POSS) generated additional nanoscale pores. This multiscale pore structure enhanced both compressive strength and thermal insulation properties. The PI-CNT-POSS composite aerogel with a 2 wt% CNT content (PI-CP2) demonstrated outstanding overall performance, with compressive strength, modulus and thermal conductivity values of 167.7 KPa, 360.3 Kpa and 40.6 mW/(m·K), respectively, possessing remarkable advantages over the neat PI aerogel. Consequently, this PI composite aerogel can be used as a promising material for heat management in complex environments.

Preservation of Luminescent Properties of Zinc Complexes in the Solid State by Accumulating into Polyhedral Oligomeric Silsesquioxane

AbstractMultinuclear complexes have attracted great attention because of their superior properties originating from the cooperative effects between the metal ions. In this study, we synthesized polynuclear zinc complexes by chelation between the side‐chains of polyhedral oligomeric silsesquioxane (POSS). From the NMR spectroscopy, high‐resolution mass spectrometry and Fourier transform infrared spectroscopy (FT‐IR), it was confirmed the four equivalents of zinc ions were coordinated to the single POSS molecule. Optical measurements indicated that luminescent properties can be preserved even in the solid state. The three‐dimensional structure of POSS should play a significant role in suppressing concentration quenching followed by solid‐state emission properties.

Redox‐Active Organic Molecules Supported by Polyhedral Oligomeric Silsesquioxane

AbstractOrganic redox molecules have attracted considerable attention because of their abundant availability and excellent design flexibility. For practical applications, these molecules must be anchored onto scaffolds such as polymers to prevent crystallization and elution into the electrolyte. In this study, we explore the use of polyhedral oligomeric silsesquioxane (POSS) derivatives as scaffolds for anthraquinone (AQ) and hydroquinone. We investigated the cage structure of POSS and the number of redox units incorporated. Notably, a corner‐opened POSS (CO‐POSS) variant with three AQ units exhibited reversible redox behavior under neutral, acidic, and basic conditions. Furthermore, we examined the air‐battery performance of AQ‐modified CO‐POSS as an anode‐active material.

Influence of vinyl polyhedral oligomeric silsesquioxane with different functionalities and cage structures on the mechanical properties and ablation resistance of EPDM composites

AbstractFour vinyl polyhedral oligomeric silsesquioxane (POSS) with different functionalities and cage structures, monovinyl‐POSS (monov‐POSS), divinyl‐POSS (div‐POSS), trivinyl‐POSS (triv‐POSS), and tetravinyl‐POSS (tetrav‐POSS) were prepared and blended into fiber‐reinforced ethylene propylene diene monomer (EPDM—EPDM/AF) in the form of chemical cross‐linking to obtain four modified composites with various cross‐linked network structures and cage structures to investigate the influences and improvement of cross‐linking network and cage structures on the mechanical, thermal stability and ablation resistance of EPDM/AF. The results showed that the POSS of multi‐functionality with small steric hindrance, such as tetrafunctional tetrav‐POSS, can most significantly improve mechanical properties of EPDM/AF by forming denser crosslinking network structures, and the tensile strength and elongation at break of EPDM/AF/tetrav‐POSS can be increased 73.3% and 42.1% compared with EPDM/AF, respectively. POSS that has a complete cage structure and enables the modified composites to obtain a relatively dense cross‐linked network structure, such as difunctional div‐POSS can more substantially enhance the thermal stability and ablative resistance of EPDM/AF with the LAR and MAR of EPDM/AF/div‐POSS reduced by 25.2% and 10.5% compared to EPDM/AF, respectively. High‐temperature thermal transition of four modified composites at gradient temperatures was investigated to explain the relationship between the structure of POSS and ablation properties.Highlights Four POSS with different functionalities and cage structures were designed. Mechanical and ablative properties were reinforced by four vinyl POSS. Multifunctional POSS can most significantly improve mechanical properties. Functionality and cage structure together influence ablative property. High‐temperature thermal transition of modified composites was investigated

"Clicking" trimeric peptides onto hybrid T8POSS nanocages and identifying synthesis limitations.

Macromolecule branching upon polyhedral oligomeric silsesquioxanes (POSS) via "click" chemistry has previously been reported for promoting natural biological responses in vitro, particularly when regarding their demonstrated biocompatibility and structural robustness as potential macromolecule anchoring points. However, "clicking" of large molecules around POSS structures uncovers two main challenges: (1) a synthetic challenge encompassing multi-covalent attachment of macromolecules to a single nanoscale-central position, and (2) purification and separation of fully adorned nanocages from those that are incomplete due to their similar physical characteristics. Here we present peptide decoration to a T8POSS nanocage through the attachment of azido-modified trimers. Triglycine- and trialanine-methyl esters "clicked" to 97% and 92% completion, respectively, resulting in 84% and 68% yields of the fully-adorned octamers. The "clicks" halt within 27-h of the reaction time, and efforts to further increase the octamer yield were of negligible benefit. Exploration of reaction conditions reveals multiple factors preventing full octa-arm modification to all available POSS nanocages, and offers insights into macromolecule attachment between both peptides and small inorganic-organic structures, all of which require consideration for future work of this nature.

A "Green" Stirring Plasma Functionalization Strategy for Controllable Oxygen-Containing Functional Groups on Octa-Methyl POSS Microstructure.

The distinctive cage-like structure of polyhedral oligomeric silsesquioxane (POSS) materials makes them highly effective fillers in composite membranes for separation applications. However, realizing their full potential in the application often requires specific surface functionalization with various groups. However, this requirement remains challenging owing to the limitations of wet-chemistry approaches, which frequently result in the generation of hazardous chemical by-products. In this paper, a "green" stirring plasma strategy is presented for the functionalization of octa-methyl POSS sub-micron particles into designable oxygen-containing functional groups using a low-pressure oxygen plasma from combined continuous wave and pulsed (CW+P) modes. Plasma from oxygen gas with CW mode offers highly oxygen-reactive species to continuously etch and activate the surface of the POSS. The resulting pulsed plasma assists in grafting more reactive oxygen species onto the active methyl groups of the POSS to form specific oxygen-containing functional groups including hydroxyl and carboxyl. A precise control of nearly one hydroxyl or one carboxyl group at the corner of the cage structure of the POSS is demonstrated, without damaging the core. Therefore, the plasma process discussed in this work is suggested by the authors as controllable fundamental research for the surface functionalization of sub-micron particles, promoting a more environmentally friendly pathway for the preparation of designable fillers.

In situ formation of POSS layer on the surface of polyimide film and anti-atomic oxygen of SiO2/POSS coatings

Polyhedral oligomeric silsesquioxane (POSS) nanoparticles have attracted wide attention due to their unique capability to reinforce polymers. However, if POSS cannot be uniformly dispersed in the polymer matrix, the desired properties of composites will be reduced. To solve this problem, a method of in situ formation of POSS layer on the surface of polyimide (Kapton) was explored, which not only kept the original properties of polymer unaffected, but also endowed the composites with new properties. The Kapton film completely wetted by γ-aminopropyltriethoxysilane (APTES) was placed in a solution containing tetraethylammonium hydroxide (TEAOH) catalyst, and a POSS layer was gradually grown on the Kapton surface. Subsequently, SiO2 coating was deposited on the surface of POSS layer by magnetron sputtering to prepare SiO2/POSS/Kapton (SPK) samples. FTIR and XPS analyses showed that a layer with POSS structure was formed on the surface of Kapton after 6 h self-growth. Atomic oxygen irradiation test shows that the erosion rate of 6 h SPK sample is 0.19 × 10−24 cm3/atom, only equivalent to 6.0 % of original Kapton, which improves the corrosion resistance of polymer materials.

Preparation of bisDOPO-NH2-POSS flame retardant and its application to plywood using modified urea-formaldehyde resin

ABSTRACT A new type of polyhedral oligomeric silsesquioxanes bisDOPO-NH2-POSS flame retardant consisting of one polyhedral oligomeric silsesquioxane (POSS), two units of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and reactive –NH2 groups, was synthesized and characterized by FTIR, 1H NMR, and 31P NMR. It was applied to modified conventional environmentally friendly E0 grade urea formaldehyde (UF) resin to prepare flame-retardant plywood. Two other POSS structure flame retardants were used for comparison. The results showed that the addition of bisDOPO-NH2-POSS flame retardant to E0 UF resin improved bonding strength while lowering formaldehyde emission owing to the increase in cross-linking of the UF molecule chain in condensation. TGA curves showed that bisDOPO-NH2-POSS-E0 UF exhibited the highest thermal stability. The flammability characteristics of the plywood were evaluated by a cone calorimeter test (CCT), and the results indicated that the heat release and smoke production of flame-retardant plywood were lower than those of the control E0-UF plywood. Moreover, compared to E0-UF plywood, the char residue remaining after the CCT test of the flame-retardant plywood with POSS structure increased. In particular, bisDOPO-NH2-POSS-E0-plywood had a continual compact outer carbon layer, which was conducive to effectively forming a physical barrier to hinder the penetration of oxygen and heat and exhibiting the outstanding synergistic effect of phosphorous, silicon and nitrogen.

Synthesis of Functionalized Silsesquioxane Nanomaterials by Rhodium‐Catalyzed Carbene Insertion into Si−H Bonds

AbstractWe report carbene insertion into Si−H bonds of polyhedral oligomeric silsesquioxanes (POSS) for the synthesis of highly functionalized siloxane nanomaterials. Dirhodium(II) carboxylates catalyze insertion of aryl‐diazoacetates as carbene precursors to afford POSS structures containing both ester and aryl groups as orthogonal functional handles for further derivatization of POSS materials. Four diverse and structurally varied silsesquioxane core scaffolds with one, three, or eight Si−H bonds were evaluated with diazo reactants to produce a total of 20 new POSS compounds. Novel diazo compounds containing a fluorinated octyl group and boron‐dipyrromethene (BODIPY) chromophore demonstrate the use of highly functionalized substrates. Transformations of aryl(ester)‐functionalized POSS compounds derived from this method are demonstrated, including ester hydrolysis and Suzuki–Miyaura cross‐coupling.

Synthesis of Functionalized Silsesquioxane Nanomaterials by Rhodium-Catalyzed Carbene Insertion into Si-H Bonds.

We report carbene insertion into Si-H bonds of polyhedral oligomeric silsesquioxanes (POSS) for the synthesis of highly functionalized siloxane nanomaterials. Dirhodium(II) carboxylates catalyze insertion of aryl-diazoacetates as carbene precursors to afford POSS structures containing both ester and aryl groups as orthogonal functional handles for further derivatization of POSS materials. Four diverse and structurally varied silsesquioxane core scaffolds with one, three, or eight Si-H bonds were evaluated with diazo reactants to produce a total of 20 new POSS compounds. Novel diazo compounds containing a fluorinated octyl group and boron-dipyrromethene (BODIPY) chromophore demonstrate the use of highly functionalized substrates. Transformations of aryl(ester)-functionalized POSS compounds derived from this method are demonstrated, including ester hydrolysis and Suzuki-Miyaura cross-coupling.

Modified POSS nano-structures as novel co-initiator-crosslinker: Synthesis and characterization

ObjectiveTo synthesize an amine-modified polyhedral oligomeric silsesquioxane (POSS) nano-structure as a novel co-initiator-crosslinker (co-Ini-Linker) and to determine the effect of the co-Ini-linker on the physical and mechanical behavior of an experimental dental composite. MethodsThe amine-methacrylate POSS nano-structures (AMA-POSS) were chemically synthesized by anchoring a tertiary amine functionality on the methacrylate POSS (MA-POSS) branches. Three types of AMA-POSS, having different amine branches in their structures, were synthesized through the Aza Michael reaction. The chemical structure of AMA-POSSs were evaluated by1H-NMR spectroscopy. Afterward, the AMA-POSS was incorporated into a dental resin system composed of Bis-GMA, TEGDMA, and photo-initiator. Three resin systems with different AMA-POSS types were then prepared, and their properties were compared with a resin containing DMAEMA as a conventional co-initiator. The degree of conversion evaluated by FTIR spectroscopy and the shrinkage kinetics of the resins were determined through the bonded-disk technique. The flexural properties of the photopolymerized resins were also investigated. The distribution of nano-structures in the matrix resin was analyzed using EDX analysis. ResultsThe modified POSS structure and the number of amine branches were confirmed with1H-NMR spectroscopy. The resin containing 8 amine branches (P8) showed the same degree of conversion (DC%) as the resin containing DMAEMA (P > 0.05). Decreasing the amine branches in the POSS structure, however, revealed an increasing trend in DC%. The resin containing P8 showed the lowest shrinkage strain. By incorporating AMA-POSS into the resin system, the water sorption significantly decreased (P < 0.05). The flexural strength and modulus increased by adding P3 into the resin system (P < 0.05). EDX Si-map revealed that the co-Ini-linker was well dispersed in the resin matrix. SignificanceThe synthesized novel amine-methacrylate POSS nanostructures not only act as an amine co-initiator but also work as a reinforcing filler and a cross-linking agent.

Kinetic Analysis on the Stabilization Effects of Substituted POSS Powders Embedded in γ-Radiolyzed Polypropylene

The present paper proposes a reliable alternative for the increasing stability of polypropylene (PP) by modified polyhedral oligomeric silsesquioxanes (POSS). The chemiluminescence measurements and FTIR records point complementarily out the determinant influence of substituents on the progress of oxidation during the accelerated degradation caused by γ-irradiation. The main kinetic approach of oxidation acting in radiation-induced aging recommends some of the studied structures of modified POSS as appropriate compounds for improving stability of polypropylene at low additive concentration. The analysis of the present results is based on the implication of substituted POSS, whose contribution to the limitation of oxidation is conditioned by the influence of substituents. The delay of the oxidative degradation in studied γ-irradiated polypropylene is the consequence of the interaction between molecular PP fragments and the silanol moieties generated during radiolysis, which are the most vulnerable points of POSS structure.

Behaviour of PLA/POSS nanocomposites: Effects of filler content, functional group and copolymer compatibilization

The main purpose of this study was to investigate influences of three parameters on the mechanical and thermal properties of the polylactide (PLA) matrix nanocomposites filled with polyhedral oligomeric silsesquioxane (POSS) particles. For the first parameter of “Filler Content”, nanocomposites with 1, 3, 5, 7 wt% basic POSS structure were compared. For the second parameter of “Functional Group,” basic POSS structure having only nonpolar isobutyl groups were compared with three other functionalized POSS structures; i.e. aminopropylisobutyl-POSS (ap-POSS), propanediolisobutyl-POSS (pd-POSS) and octasilane-POSS (os-POSS). Finally, for the third parameter of “Copolymer Compatibilization,” all specimens were compared before and after their maleic anhydride (MA) grafted copolymer compatibilization. Specimens were produced with twin-screw extruder melt mixing and shaped under compression molding. Various tests and analyses indicated that the optimum filler content for the improved mechanical properties was 1 wt%; while the optimum structure for strength and modulus was pd-POSS structure, in terms of fracture toughness it was basic POSS structure. Additional use of MA compatibilization was especially effective for the basic POSS and os-POSS particles.

Thioxanthone attached polyhedral oligomeric silsesquioxane (POSS) nano-photoinitiator for preparation of PMMA hybrid networks in air atmosphere

2-(9-Oxo-9H-thioxanthene-2-yloxy)-N-(3-silsesquioxanylpropyl) acetamide was synthesized with 2-(carboxymethoxy) thioxanthone and aminopropylisobutyl POSS as precursors. Absorption characteristics of 2-(9-Oxo-9H-thioxanthene-2-yloxy)-N-(3-silsesquioxanylpropyl) acetamide is similar to the thioxanthone, even its molar absorptivity is much higher than bare precursor thioxanthone. The one-component nature of this nano-photoinitiator allowed us to use it as a photoinitiator even in the air atmosphere. Initiation mechanism of 2-(9-oxo-9H-thioxanthene-2-yloxy)-N-(3-silsesquioxanylpropyl) acetamide is based on intramolecular hydrogen abstraction and resulted alkyl radical which initiate polymerization. Intramolecular hydrogen abstraction of 2-(9-oxo-9H-thioxanthene-2-yloxy)-N-(3-silsesquioxanylpropyl) acetamide ends up as the covalent linkage of POSS structure to the polymer. The important contribution of incorporation and good dispersion of POSS in poly(methyl methacrylate) matrices were observed as an improve in thermal stability and led to the formation of robust polymer/filler network. Poly(methyl methacrylate) hybrid network prepared with 2-(9-oxo-9H-thioxanthene-2-yloxy)-N-(3-silsesquioxanylpropyl) and aminopropylisobutyl POSS / 2-(carboxymethoxy) thioxanthone and scanning electron microscopy images of casts film surfaces presented two different views. First formulation displayed smaller and more homogeneous pores. Second formulation, which contains two component system, led to disordered porous structures.

First-principles insights into atomic oxygen diffusion inside polyhedral oligomeric silsesquioxane cages

Atomic oxygen erosion is a significant threat to exterior spacecraft polymers. Polyhedral oligomeric silsesquioxane (POSS) is a potential kind of material in resisting AO diffusion erosion, but lack of mechanism studies for application supports. In this research, we used the first-principles calculations to investigate the mechanism based on two types of nominally hydrated POSS named T8 (Si8O12H8) and T10 (Si10O15H10). According to the results, we found that the minimum energy path (MEP) of AO diffusing inside POSS is the adjacent-edge-path rather than the center-path. We also found the energy barriers that hinder the diffusion motion of AO inside POSS are originated from the structural distortion of POSS, which are negatively correlated to Si-O bond length and positively correlated to structural compactness. Thus, compacter POSS structures with shorter Si-O bond length are expected to give better AO diffusion resistance properties.

The effect of incompletely condensed polyhedral oligomeric silsesquioxanes (POSS) on hybrid film adhesion

The objective of this study was to investigate the influence of polyhedral oligomeric silsesquioxane (POSS) structure on the adhesion behaviour of composite films onto a metallic surface. The composite films consisted of UV cured bisphenol A glycidylmethacrylate/triethylene glycol dimethacrylate (Bis-GMA/TEGDMA) as matrix and reactive POSS structures as adhesion enhancers. Composites were made with 1, 3 and 5 wt % of POSS. Adhesion was evaluated using the micro Vickers hardness testing method. The contact angle of composite films to a brass substrate was measured and compared to the adhesion parameter obtained from microhardness measurements. Optical microscopy indicated morphological segregation in the hybrid films suggesting the compatibility extent between the matrix and each particle. The shape and size of the indent were analyzed and correlated with adhesion quality. The methods used for the estimation of adhesion strength and quality clearly indicated that the highest adhesion enhancement of the Bis-GMA/TEGDMA matrix was POSS reagent containing both polar (hydroxyl) and nonpolar (unsaturated aliphatic - allyl) side groups.

Polyhedral oligomeric silsesquioxane/epoxy coatings: a review

Nowadays, there is a need for a paradigm shift in material selection for surface coatings so as to meet the requirements of advanced systems. Polyhedral oligomeric silsesquioxanes (POSS) are three-dimensional networks with a silica-like core covered by an organic shell, a promising nanosized structure for organic coatings. The use of POSS structures in coating materials has experienced an almost erratic period over the past decade, mainly because of the synthesis of POSS being exclusive and, to some extent, expressive. However, there has been a big return to the use of POSS in coatings during the last years. Epoxy is best known for its versatility of usage as an organic coating. Hybrid organic–inorganic POSS nanostructures with unique properties are a complement to the epoxy for coating applications. The tailorable compatibility and considerable reactivity of POSS molecules towards organic groups have made them promising candidates for emerging multifunctional epoxy coatings. In this sense, the focus of this review is placed on POSS/epoxy nanocomposite coatings. The thermal, mechanical, anti-corrosion and dielectric properties of POSS/epoxy coatings have been comprehensively studied and discussed.

Optimizing the monomer structure of polyhedral oligomeric silsesquioxane for ion transport in hybrid organic–inorganic block copolymers

ABSTRACTPoly(ethylene oxide)‐b‐polyhedral oligomeric silsesquioxane (PEO–POSS) mixed with lithium bis(trifluoromethanesulfonyl)imide salt is a nanostructured hybrid organic–inorganic block copolymer electrolyte that may enable lithium metal batteries. The synthesis and characteristics of three PEO–POSS block copolymer electrolytes which only differ by their POSS silica cage substituents (ethyl, isobutyl, and isooctyl) is reported. Changing the POSS monomer structure results in differences in both thermodynamics and ion transport. All three neat polymers exhibit lamellar morphologies. Adding salt results in the formation of a disordered window which closes and gives way to lamellae at higher salt concentrations. The width of disordered window decreases with increasing length of the POSS alkyl chain substituent from ethyl to isobutyl and is absent in the isooctyl sample. Rheological measurements demonstrate good mechanical rigidity when compared with similar all‐organic block copolymers. While salt diffusion coefficient and current ratio are unaffected by substituent length, ionic conductivity increases as the length of the alkyl chain substituent decreases: the ethyl substituent is optimal for ion transport. This is surprising because conventional wisdom suggests that ion transport occurs primarily in the PEO‐rich domains, that is, ion transport should be unaffected by substituent length after accounting for the minor change in conducting phase volume fraction. © 2020 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2020 © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 363–371

A robust immobilization strategy in the nano-dispersed Ziegler-Natta catalyst: non-covalent O-Ti coordination.

An immobilization strategy of catalytic TiCl4 on polyhedral oligomeric silsesquioxanes (POSSs) is developed, which features both robustness and equivalence of active sites in ethylene polymerization thanks to the non-covalent O-Ti coordination. The symmetric structure of POSS homogenizes the coordination of the TiCl4 molecules, enabling considerable activity in the synthesis of narrowly distributed polyethylene.

Control of Crystalline-Amorphous Structures of Polyhedral Oligomeric Silsesquioxanes Containing Two Types of Ammonium Side-Chain Groups and Their Properties as Protic Ionic Liquids.

Polyhedral oligomeric silsesquioxanes (POSSs), Am-POSS(x,y), prepared by hydrolytic condensation, contains two types of ammonium side-chain groups, where the numbering of x and y represents the type of ammonium ions in the POSS structure, corresponding to primary (1), secondary (2), tertiary (3), and quaternary (4) ammonium ions. Mixtures of the two starting materials selected from organotrialkoxysilanes containing primary, secondary, and tertiary amines and a quaternary ammonium salt [(RO)3Si(CH2)3R′, R = CH3 or CH2CH3, R′ = NH2, NHCH3, N(CH3)2, and N(CH3)3Cl] were dissolved in dimethyl sulfoxide (DMSO). The hydrolytic condensation was performed in the presence of bis(trifluoromethansulfonyl)imide (HNTf2) and water. All Am-POSS(x,y) structures consisted of a cage-type octamer (T8-POSS), as confirmed by 29Si NMR spectrometry and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analyses indicated that Am-POSS(1,3), Am-POSS(1,4), and Am-POSS(2,4) had amorphous structures. These POSSs have two or three differences in the number of methyl groups between the two types of ammonium side-chains. Conversely, Am-POSS(1,2), Am-POSS(2,3), and Am-POSS(3,4) had crystalline structures. The difference in the number of methyl groups between the two types of ammonium side-chains in these POSSs is only one. Therefore, the crystalline-amorphous structure of Am-POSS(x,y) is controlled by the side-chain group combinations. Furthermore, Am-POSS(1,3), Am-POSS(1,4), and Am-POSS(2,4) are protic ionic liquids with relatively low flow temperatures.