Properties Of Polyhedral Oligomeric Silsesquioxane Research Articles

Phenyl-Substituted Cage Silsesquioxane-Based Star-Shaped Giant Molecular Clusters: Synthesis, Properties, and Surface Segregation Behavior.

The crystallinity, solubility, and physical properties of polyhedral oligomeric silsesquioxane (POSS) compounds are highly dependent on their organic substituents. We previously synthesized a series of isobutyl-substituted star-shaped POSS derivatives with aliphatic chain linkers of different length. In this study, we prepared C3- and C6-linked phenyl-substituted star-shaped POSS derivatives (3Ph-C3 and 3Ph-C6) by the hydrosilylation of heptaphenylallyl- and hexenyl-POSS (1a and 1b) and octadimethylsiloxy-Q8-silsesquioxane (Q8M8H) (2), respectively, and their properties were compared with those of the corresponding isobutyl-substituted derivatives (5iBu-C3 and 5iBu-C6). Although 3Ph-C6 was only soluble in chloroform and insoluble in tetrahydrofuran (THF) and toluene, 3Ph-C3 was soluble even in THF and toluene, suggesting that the shorter linkers of the derivative afford a wider range of solvents for dissolution. Differential scanning calorimetry analysis showed that 3Ph-C3 exhibited a baseline shift at 190 °C and an endothermic peak at 316 °C. However, no clear baseline shift was observed for 3Ph-C6. Thermogravimetric analysis showed that the shorter linker in the phenyl-substituted star-shaped POSS derivative significantly increased the decomposition temperature compared with the longer linker. The annealed cast film of 3Ph-C3 at 340 °C above its melting temperature formed a transparent film even after cooling to room temperature. However, an opaque whitish film was formed in the case of 3Ph-C6. Poly(methyl methacrylate) (PMMA) films containing 2 wt % 3Ph-C3 and 3Ph-C6 were prepared by casting their chloroform solutions onto glass substrates overnight at room temperature. The static water contact angle measurements and XPS analysis for the castings film containing 3Ph-C3 and 3Ph-C6 suggested that degree of the segregation amount of 3Ph-C3 was larger than that of 3Ph-C6. The shorter linker length in the phenyl-substituted star-shaped POSS derivative, 3Ph-C3, with its greater predicted solubility in PMMA, exhibited entropy-driven surface segregation.

Effects of thiol‐ene click reaction on morphology and electro‐optical properties of polyhedral oligomeric silsesquioxane nanostructure‐based polymer dispersed liquid crystal film

AbstractPolymer dispersed liquid crystals (PDLCs) have lit a flash of interest due to the distinctive property of electrically controlled switching. However, too high‐driving voltage associated with porous polymer networks always limit their wider range of applications. Herein, we reported a PDLC system containing LCs, 2,2′‐(Ethylenedioxy)diethanethiol (DET) with thiol groups, cage‐like nanostructure acrylic polyhedral oligomeric silsesquioxane (KH570‐POSS) and KH570‐SiO2 nanoparticle modified by acrylic groups. The cage‐like KH570‐POSS microstructure was injected to the polymer matrix when KH570‐POSS reacted with DET via thiol‐ene click reaction. The morphological results demonstrated that the droplet size increased with the higher content of DET due to the decrease of the crosslink between the acrylic groups in KH570‐POSS, which results in a less dense of polymer network and thus make the LC droplets easier to be driven in the electric filed. Then, a silica‐based nanoparticle KH570‐SiO2 modified by acrylic groups was introduced into the system. The results indicated that KH570‐SiO2 could replace partial KH570‐POSS to form the polymer network via thiol‐ene click reaction, which increased the compatible ability of SiO2 nanoparticles in the as‐made film. The contrast ratio was increased to 165 when there was nearly 5 wt% content of KH570‐SiO2. Besides, the driving voltage was reduced by almost 60% and the sample could be fully driven by 30 V which is lower than the safe voltage (36 V). This study opens a route for the preparation of commercial PDLC films by thiol‐ene click reaction, enabling the creation of low‐voltage‐driven smart windows.

Fabrication and Mechanical Properties of POSS Coated CNTs Reinforced Expancel Foam Core Sandwich Structures

Background: Sandwich structures are progressively being used in various engineering applications due to the superior bending-stiffness-to-weight ratio of these structures. We adapted a novel technique to incorporate carbon nanotubes (CNTs) and polyhedral oligomeric silsesquioxanes (POSS) into a sandwich composite structure utilizing a sonochemical and high temperature vacuum assisted resin transfer molding technique. Objective: The objective of this work was to create a sandwich composite structure comprising of a nanophased foam core and reinforced nanophased face sheets, and to examine the thermal and mechanical properties of the structure. To prepare the sandwich structure, POSS nanoparticles were sonochemically attached to CNTs and dispersed in a high temperature resin system to make the face sheet materials and also coated on expandable thermoplastic microspheres for the fabrication of foam core materials. Methods: The nanophased foam core was fabricated with POSS infused thermoplastic microspheres (Expancel) using a Tetrahedron MTP-14 programmable compression molder. The reinforced nanophased face sheet was fabricated by infusing POSS coated CNT in epoxy resin and then curing into a compression stainless steel mold. Result: Thermal analysis of POSS-infused thermoplastic microspheres foam (TMF) showed an increase in thermal stability in both nitrogen and oxygen atmospheres, 19% increase in thermal residue were observed for 4 wt% GI-POSS TMF compared to neat TMF. Quasi-static compression results indicated significant increases (73%) in compressive modulus, and an increase (5%) in compressive strength for the 1 wt% EC-POSS/CNTs resin system. The nanophased sandwich structure constructed from the above resin system and the foam core system displayed an increase (9%) in modulus over the neat sandwich structure. Conclusion: The incorporation of POSS-nanofillier in the foam core and POSS-coated nanotubes in the face sheet significantly improved the thermal and mechanical properties of sandwich structure. Furthermore, the sandwich structure that was constructed from nanophased resin system showed an increase in modulus, with buckling in the foam core but no visible cracking.

A POSS-Phosphazene Based Porous Material for Adsorption of Metal Ions from Water.

The development of adsorptive materials continues to be an important area of research for removal of heavy metal ions from waste water. The adsorption capacity can be modulated by both physical and chemical modification of the adsorbent. Herein, we combine the unique properties of polyhedral oligomeric silsesquioxane (POSS) and organocyclophosphazene as the building units to synthesize a hybrid porous material, abbreviated as PN-POSS. The synthetic method follows a Heck reaction between hexa(4-bromophenoxy)cyclotriphosphazene and octavinylsilsesquioxane (OVS). The Brunauer-Emmett-Teller (BET) analysis shows that the material possesses micro- and mesopores of 1.5 and 3.8 nm size and a surface area on the order of 500 m2 g-1 . These attributes in combination with the donor ability of the phosphazene units qualify the material for high adsorption of Pb2+ , Hg2+ and Cu2+ ions with maximal adsorption capacities on the order of 1326, 1927 and 2654 mg g-1 , respectively. The adsorbent exhibits a good regeneration performance and can be effectively used for water treatment.

The effect of solvent on the mechanical properties of polyhedral oligomeric silsesquioxane (POSS)–epoxy nanocomposites

The present study investigated the influence of different compatibilizer on the dispersion of polyhedral oligomeric silsesquioxane (POSS). The effect of POSS dispersion in the epoxy resin in terms of mechanical, and thermal properties were reported. The three solvent used to disperse POSS in this work are ethanol, acetone, and toluene. The POSS was initially dispersed in the solvent followed by an addition in the epoxy resin by systematically varying the weight fraction from 0.5 to 8 wt%. Mechanical properties of nanocomposites were characterized in terms of elastic modulus, and fracture toughness. The obtained result illustrates that nanocomposites prepared by polar solvent dispersion such as ethanol showed an increase in values of elastic modulus and fracture toughness value. The increase in the modulus and fracture toughness value is due to the better interaction between POSS and ethanol disperse the POSS uniformly in the epoxy resin while avoiding the agglomeration. However, nanocomposites prepared by nonpolar solvent does not show substantial change in the mechanical properties. Fractured surface morphology was studied using scanning electron microscopy. Differential scanning calorimetry and dynamic mechanical analysis illustrates that with better POSS dispersion value of glass transition temperature (Tg) increased. Fourier transformation infrared spectroscopy showed that POSS completely interacted with the epoxy resin and no phase separation was observed.

Facile preparation and properties of polyhedral oligomeric silsesquioxane (POSS) nano-hybrid materials with disaggregation effect

This work reports on a facile and efficient strategy for preparing a class of chromophores- including organic-inorganic functional hybrid materials. These hybrid materials are based on pyrene and octavinyl-polyhedral oligomeric silsesquioxane (OV-POSS), in which the positive vinyls in OV-POSS were heck coupling reacted with pyrenes. It was found that the incorporation of polyhedral oligomeric silsesquioxane (POSS) can significantly precluded aggregation of hybrid molecules due to the inhibition of π-π stacking between chromophore units, which were also further confirmed by theoretical simulation. Moreover, the fluorescence quantum efficient of H2 (Φsolid = 80%) is higher than H1 (Φsolid = 65%) and H3 (Φsolid = 68%), respectively. AFM and OM images showed the smooth surface structure of the hybrid film, which demonstrated that the incorporation of inorganic POSS could improve the film-forming property of organic chromophores. Simultaneously, thermogravimetric analysis (TGA) results also display inorganic POSS core leads to the good thermal stabilities (>250 °C) of the functional hybrids materials.

Quantitative evaluation of the effect of dispersion techniques on the mechanical properties of polyhedral oligomeric silsesquioxane (POSS)–epoxy nanocomposites

This experimental study investigates the effects of dispersion techniques on the mechanical properties of POSS‐epoxy nanocomposites. The POSS is dispersed into the epoxy resin by stoichiometrically varying the weight fraction from 0.5 to 10 wt% and materials are prepared using three different dispersion techniques. Various mechanical properties are reported as functions of processing parameters and weight fractions. It is found that the nanocomposites with highly dispersed POSS show higher modulus and toughness values. For example, nanocomposites prepared by ultrasonication show increases in elastic and flexural modulus values by average amounts of 23% and 15%, respectively. Also, it is found that fracture toughness values increased for all three processing techniques, with the highest increase by an average of 50% at 8 wt% of POSS inclusion for nanocomposites prepared by ultrasonication. TEM images of the nanocomposites demonstrate that the properties are also affected by the formation of soft domains at higher loading levels of POSS. Further evidence on the soft domains is found in the variations of Tg. FTIR spectroscopy shows evidence of SiOSi stretching, again suggesting the formation of compliant domains due to POSS‐POSS agglomeration. POLYM. COMPOS., 39:E2445–E2453, 2018. © 2018 Society of Plastics Engineers

Facile Synthesis and Self-Assembly of Amphiphilic Polyether-Octafunctionalized Polyhedral Oligomeric Silsesquioxane via Thiol-Ene Click Reaction.

We demonstrated here a facile and efficient synthesis of polyhedral oligomeric silsesquioxane-based amphiphilic polymer by thiol-ene click chemistry. The properties of polyhedral oligomeric silsesquioxane (POSS)–PEG amphiphilic polymers were studied in detail by a combination of 1H NMR, 13C NMR, 29Si NMR FT-IR, GPC, and TG analysis. The newly-designed thiol-ene protocol obtains only anti-Markovnikov addition POSS-based amphiphilic polymers when compared with platinum-catalysed hydrosilylation method. The critical micelle concentration (CMC) of the resulting polymers are in the range of 0.011 to 0.050 mg/mL, and dynamic light scattering (DLS) results revealed that the obtained amphiphilic polymers can self-assemble into nanoparticles in aqueous solutions with a bimodal (two peaks) distribution. Furthermore, the specific polymer showed obvious thermo-sensitive behaviour at 45.5 °C.

Polyhedral oligomeric silsesquioxanes (POSSs): an important building block for organic optoelectronic materials

Due to the unique hybrid structures and physical properties of polyhedral oligomeric silsesquioxanes (POSSs), hybridation with POSS has been demonstrated to be an important approach to build high-performance organic optoelectronic materials for applications in organic light-emitting diodes (OLEDs), liquid crystal display, sensors and electrochromic devices.

Dielectric properties of polyhedral oligomeric silsesquioxane (POSS)-based nanocomposites at 77k

The goal of this study is to develop dielectric nanocomposites for high energy density applications at liquid nitrogen temperature by utilizing a unique nano-material polyhedral oligomeric silsesquioxanes (POSS). A POSS molecule is consisted of a silica cage core with 8 silicon and 12 oxygen atoms and organic functional groups attached to the corners of the cage. In this study, we utilize POSS for the fabrication of nanocomposites both as a silica nanoparticle filler to enhance the breakdown strength and as a surfactant for effective dispersion of high permittivity ceramic nanoparticles in a polymer matrix. The matrix materials selected for the study are polyvinylidene fluoride (PVDF) and poly(methyl methacrylate) (PMMA). The ceramic nanoparticles are barium strontium titanate (BST 50/50) and strontium titanate. The dielectric properties of the solution-cast nanocomposites films were correlated to the composition and processing conditions. We determined that the addition of POSS did not provide enhanced dielectric performance in PVDF- and PMMA-based materials at either room temperature or 77K. In addition, we found that the dielectric breakdown strength of PMMA is lower at 77K than at room temperature, contradicting literature data.

Preparation and properties of polyhedral oligomeric silsesquioxane and carbon nanotube grafted carbon fiber hierarchical reinforcing structure

A novel route of grafting carbon nanotubes onto carbon fibers using polyhedral oligomeric silsesquioxanes as coupling agents was reported. The fiber tensile strength did not show any discernable decrease. The content of surface functional groups sharply increased, and the interfacial adhesion of the resulting composites showed a dramatic improvement.

Tuning Electronic Properties of Functionalized Polyhedral Oligomeric Silsesquioxanes: A DFT and TDDFT Study

The structure and electronic properties of polyhedral oligomeric silsesquioxane (POSS) cages functionalized with different organic groups have been studied using density functional theory and time-dependent density functional theory calculations. Accordingly, the POSS-T8 cage is quite rigid upon functionalization and thus provides a means for spatially separating conjugated organic fragments, which is useful for the realization of novel organic molecular architectures for light-emitting diodes. Moreover, electronic properties can be tuned through the choice of functional groups and their positioning on or within the POSS cage. Attaching an electron-donating group, such as 4-carbazolephenyl, to the silicon atom at the corner of the cage raises the HOMO level, while attaching an electron-withdrawing group, such as 4-cyanophenyl, or inserting an inert molecule, such as N(2), into the POSS cage lowers the LUMO level. Frontier orbital analysis indicates that the POSS cage is partially conjugated and serves a role as electron acceptor. Carrier transport rates are discussed in the frame of Marcus' electron hopping theory. On the basis of the calculated reorganization energies, these POSS compounds can be used as carrier transporting or blocking materials, depending on the functionalization. Exciton binding energies strongly depend on the spatial arrangement of frontier orbitals rather than on molecular sizes.

Thermal and mechanical properties of polyhedral oligomeric silsesquioxane (POSS)/polycarbonate composites

A series of composite materials were produced incorporating polyhedral oligomeric silsesquioxane (POSS) derivatives into polycarbonate (PC), by melt blending. Significant differences in compatibility were observed depending on the nano-scale filler's specific structure: trisilanol POSS molecules generally provided better compatibility with PC than fully-saturated cage structures, and phenyl-substituted POSS grades were shown to be more compatible with PC than fillers with other functional groups. Trisilanolphenyl-POSS/PC composites possess the best overall performance among the POSS materials tested. The high compatibility between the trisilanolphenyl-POSS and polycarbonate matrix results in generation of transparent samples up to 5 wt% POSS content. Slightly enhanced mechanical properties including tensile and dynamic mechanical modulus are observed with the increase of trisilanolphenyl-POSS loading at the cost of decreasing ductility of the nanocomposites. Importantly, upon orientation of the PC/POSS nanocomposite, crystallization of POSS within the oriented material results—this observation is consistent with a growing number of observations which suggest that ‘bottom-up’ formation of structures incorporating multiple POSS cages result from orientation of these nanocomposites, and that the hybrid organic–inorganic inclusions may be at the heart of observed nano-scale reinforcement.

Structure of Hybrid Polyhedral Oligomeric Silsesquioxane Propyl Methacrylate Oligomers Using Ion Mobility Mass Spectrometry and Molecular Mechanics

Ion mobility and molecular modeling methods were used to examine the gas phase conformational properties of polyhedral oligomeric silsesquioxanes (POSS) propyl methacrylate (PMA) oligomers. MALDI was utilized to generate sodiated [(PMA)Cp7T8]xNa+ ions, x = 1, 2, and 3, and their collision cross-sections were measured in helium using ion mobility based methods. Experimental results indicate only one conformer for the Na+1-mer and Na+3-mer, but two or more conformers for the Na+2-mer. Theoretical modeling of the Na+1-mer using the AMBER suite of programs indicates only one family of low-energy structures is found, in which the sodium ion binds to the carbonyl oxygen on the PMA and 4 oxygens on one face of the POSS cage. The calculated cross-section of this family agrees very well with the experimental value, with <2% deviation. For the Na+2-mer, theory predicts three separate conformer families based on whether the backbone attachments to the two POSS cages are “cis”, “extended trans” (larger), or “trans” (...

Mechanical properties of polyhedral oligomeric silsesquioxane (POSS) thin films submitted to Si irradiation

The nanoindentation technique was used to measure hardness and elastic modulus of polyhedral oligomeric silsesquioxane (POSS) thin films irradiated with 1 MeV Si ions. The fluences ranged from 10 13 to 10 16 Si + cm −2, corresponding to averaged deposited energy densities from 0.3 to 70 eV/A 3. Elastic recoil detection analysis, nuclear reaction analysis, infrared (FTIR) and Raman spectroscopy were used to characterize the compositional changes as a function of the deposited energy by the Si irradiation. The film starts to decompose at the lowest fluence reaching progressively an amorphous structure of Si–O–Si at the highest fluence. The hardness and elastic modulus of the pristine film are 0.11 and 5 GPa, respectively. At the highest Si fluence, the hardness and elastic modulus reaches around 6 and 65 GPa, respectively, that are typical values for silicate glasses (Si–O–Si).