Preparation and properties of polyhedral oligomeric silsesquioxane polymers

Polyhedral oligomeric silsesquioxane (POSS) polymers were synthesized by the dehydrogenative condensation of (HSiO_3/2)₈ with water in the presence of diethylhydroxylamine followed by trimethylsilylation. Coating films were prepared by spin‐coating of the coating solution prepared by the dehydrogenative condensation of POSS. The hardness of the coating films was evaluated using a pencil‐hardness test and was found to increase up to 8H with increases in the curing temperature. Free‐standing film and silica gel powder were prepared by aging the coating solution at room temperature. The silica gel powder was subjected to heat treatment under air atmosphere to show a specific surface area of 440 m² g⁻¹ at 100 °C, which showed a maximum at 400 °C as 550 m² g⁻¹. Copyright © 2011 John Wiley & Sons, Ltd.     

A novel poly-benzoxazinyl functionalized polyhedral oligomeric silsesquioxane and its nanocomposite with polybenzoxazine

The novel poly-benzoxazinyl functionalized polyhedral oligomeric silsesquioxane macromonomer (BZ-POSS), containing 7.6 benzoxazine groups per molecule on average was synthesized from octaaminophenylsilsesquioxane, p-cresol and paraformaldehyde. BZ-POSS was well miscible with bisphenol A-based benzoxazine (BBZ) melt. By ring-opening copolymerization of BBZ and BZ-POSS under condition similar to that used for polymerizing neat BBZ, the transparent and uniform BBZ/BZ-POSS organic-inorganic hybrid nanocomposites were prepared. The nano-scale dispersion of POSS cores in the nanocomposite was verified by powder X-ray diffraction and transmission electron microscopy studies. Dynamic mechanical analyses and thermal gravimetric analysis indicated that thermal stabilities, cross-link densities and the flame retardance of the nanocomposites were increased in comparison with neat PBBZ resin, although only small amounts of inorganic POSS cores were incorporated into the systems. Structural analyses of BZ-POSS and BBZ/BZ-POSS nanocomposites are discussed herein.     

Flame retardant and mechanism of vinyl ester resin modified by octaphenyl polyhedral oligomeric silsesquioxane

Flamability is one of the major issues for utilization of bisphenol A–type vinyl ester resin (VER) polymeric composites in practical applications. The thermal stability and mechanical property of VER composites containing octaphenyl polyhedral oligomeric silsesquioxane (OPS) were investigated and discussed in detail. With increasing the mass ratio of OPS, the residues yield at 800°C and bending strength at break of the VER/OPS composites were enhanced, accompanied with the gradually decreased values of the peak heat release rate, total heat release, and total smoke release due to the formation of dense carbon/silica protective layers that acted as a barrier to heat and mass transfer. In addition, the flame‐retardant mechanisms of condensed phase and gas phase were analyzed by XPS, TGA‐FTIR, and GC‐MS. The results showed that when OPS was incorporated to the resin matrix, the characteristic peaks intensity of the gaseous products was reduced obviously due to some of the characteristic groups still retained in condensed phase. Therefore, the significance of this work is providing an optional method to fabricate flame‐retarding VER composites with excellent mechanical properties.     

Morphology and thermal properties of polyhedral oligomeric silsesquioxane/polybutadiene nanocomposites prepared by anionic polymerization

The morphology and thermal properties of Allylisobutyl Polyhedral Oligomeric Silsesquioxane (POSS)/Polybutadiene (PB) nanocomposites prepared through anionic polymerization technique were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results of XRD, SEM and TEM showed that the aggregation of POSS in PB matrix occurred obviously, forming crystalline domains and the size of POSS particles increased with increasing POSS content. The DSC and TGA results indicated that the glass transition temperature (T _g) of the nanocomposites was significantly increased and the maximum degradation temperature (T _dmax) of nanocomposites was slightly increased compared with pure PB, implying an increase in thermal stability.     

Surface modification of gold nanoparticles with polyhedral oligomeric silsesquioxane and incorporation within polymer matrices

A new approach to achieve polymer‐mediated gold ferromagnetic nanocomposites in a polyhedral oligomeric silsesquioxane (POSS)‐containing random copolymer matrix has been developed. Stable and narrow distributed gold nanoparticles modified by 3‐mercaptopropylisobutyl POSS to form Au‐POSS nanoparticles are prepared by two‐phase liquid‐liquid method. These Au‐POSS nanoparticles form partial particle aggregation by blending with poly(n‐butyl methacrylate) (PnBMA) homopolymer because of poor miscibility between Au‐POSS and PnBMA polymer matrix. The incorporation the POSS moiety into the PnBMA main chain as a random copolymer matrix displays well‐dispersed gold nanoparticles because the POSS‐POSS interaction enhances miscibility between gold nanoparticles and the PnBMA‐POSS copolymer matrix. This gold‐containing nanocomposite exhibits ferromagnetic phenomenon at room temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 811–819, 2009     

Novel gel polymer electrolyte based on matrix of PMMA modified with polyhedral oligomeric silsesquioxane

Journal of Solid State Electrochemistry - One novel cage kind of polyhedral ligomeric silsesquioxane (POSS), for modification application of gel polymer electrolyte (GPE) in lithium ion batteries...     

The mechanical properties of crystalline cyclopentyl polyhedral oligomeric silsesquioxane

The anisotropic elastic constants of crystalline octacyclopentyl polyhedral oligomeric silsesquioxane (CpPOSS) were determined using molecular dynamics. The force field used for these calculations was shown to model accurately the rhombohedral and triclinic crystal structures of octasilsesquioxane and CpPOSS, respectively, as well as the vibrational frequencies of octasilsesquioxane. The moduli for CpPOSS are anisotropic, with a Reuss-averaged bulk modulus of 7.5 GPa, an isotropic averaged Young's modulus of 11.78 GPa, and an isotropic averaged shear modulus of 4.75 GPa. These isotropic averages or, alternatively, the full anisotropic stiffness tensor of the crystal can be used with micromechanical composite models to calculate the effective elastic properties of polymer nanocomposites that contain crystalline aggregates of CpPOSS.     

Cross-linking of carboxyl-terminated nitrile rubber with polyhedral oligomeric silsesquioxane

Glycidyl polyhedral oligomeric silsesquioxane (POSS) was used as a cross-linking agent to prepare a new organic–inorganic hybrid material from carboxyl-terminated poly(acrylonitrile-co-butadiene) (CTBN). The structure of the reacted material was characterized by Fourier transform infrared spectroscopy. Differential scanning calorimetry (DSC) at different heating rates in the presence and absence of catalyst, triphenyl phosphine (TPP), was conducted to investigate the curing kinetics. The reaction is catalyzed by the addition of TPP, and rate is maximum at higher catalyst concentrations. Different kinetic models were used to analyze the kinetic parameters. The effect of catalyst on curing process was determined by calculating the activation energy (E _a) using Kissinger method. Dependency of E _a with extent of conversion was monitored by different isoconversional methods. The curing mechanism of POSS–CTBN system followed autocatalytic model. Moreover, the predicted curves from the kinetic models fit well with the non-isothermal DSC curve. The E _a of gelation obtained from rheological studies matched with that from DSC study, in league with the Flory’s theory of cross-linking.     

Unique rodlike surface morphologies in trisilanolcyclohexyl polyhedral oligomeric silsesquioxane films

A trisilanol derivative of polyhedral oligomeric silsesquioxane (POSS), trisilanolisobutyl-POSS, has recently been reported to form stable monolayers at the air/water interface. This paper explores the mono- and multilayer properties of another POSS derivative, trisilanolcyclohexyl-POSS, with pi-A isotherm and Brewster angle microscopy measurements. Results show that with continuously increasing surface concentration via symmetrical compression, trisilanolcyclohexyl-POSS amphiphiles at the air/water interface undergo a series of phase transitions from traditional Langmuir monolayers (one-POSS-molecule thick) to unique rodlike hydrophobic aggregates in multilayer films (approximately eight-POSS-molecules thick) that are dramatically different from "collapsed" morphologies seen in other systems. Stable and hydrophobic rodlike structure formation on water is presumably due to trisilanolcyclohexyl-POSS' unique molecular structure and strong tendency to form intermolecular hydrogen bonds in the solid state. This result is consistent with existing POSS/polymer composite research, which shows that POSS molecules tend to aggregate and crystallize into lamellar nanocrystals.     

Modified bentonite by polyhedral oligomeric silsesquioxane and quaternary ammonium salt and adsorption characteristics for dye

To remove methylene blue dye from water by adsorption, bentonites were modified by polyhedral oligomeric silsesquioxane (POSS) and three kind of quaternary ammonium surfactants (dodecyl trimethyl ammonium bromide, tetrabutyl ammonium bromide, cetyl trimethylammonium bromide) in aqueous solution. Systematic adsorption experiments were carried out, the adsorption mechanism was studied, and the factors governing the adsorption of methylene blue on modified bentonite were discussed. The adsorption capacity of methylene blue on all three modified bentonites in 1000 mg·L⁻¹ solutions quickly reached equilibrium within 2000 s, and the removal rate was basically 100%; however, the removal rate in raw bentonite samples was only 60%. The pseudo second-order kinetic model can provide satisfactory kinetic data fitting. The obtained adsorption isotherms fit well with the Dubinin-Radushkevich isotherm model. The thermodynamic results showed that the adsorption process was a spontaneous endothermic physical adsorption process. With increasing pH and KCl concentration, the removal of methylene blue increased significantly. The results of this study confirmed that the modified bentonite is a candidate material as a cationic dye adsorbent.     

Nanocomposites through copolymerization of a polyhedral oligomeric silsesquioxane and methyl methacrylate

The mechanical properties and thermal stability of polymers can be enhanced through the formation of nanocomposites. Nanocomposites consisting of hybrid copolymers of methacrylcyclohexyl polyhedral oligomeric silsesquioxane (POSS‐1) and methyl methacrylate (MMA) with up to 92 wt % (51 mol %) POSS‐1 and with superior thermal properties were synthesized using solution polymerization. The POSS‐1 contents of the copolymers were similar to or slightly higher than those in the feeds, the polydispersity indices were relatively low, and the degree of polymerization decreased with increasing POSS‐1 content. POSS‐1 enhanced the thermal stability, increasing the degradation temperature, reducing the mass loss, and preventing PMMA‐like degradation from propagating along the chain. The mass loss was reduced in a high POSS‐1 content copolymer since the polymerization of POSS‐1 with itself reduced sublimation. Exposure to 450 °C produced cyclohexyl‐POSS‐like remnants in the POSS‐1 monomer and in all the copolymers. The degradation of these remnants, for the copolymers and for the POSS‐1 monomer, yielded 75% SiO₂ and an oxidized carbonaceous residue. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4264–4275, 2007     

Rheological behavior of polypropylene/octavinyl polyhedral oligomeric silsesquioxane composites

The reactive blending composites of isotactic polypropylene (PP)/octavinyl polyhedral oligomeric silsesquioxane (POSS) were prepared in the presence of dicumyl peroxide. Comparison of the rheological behavior of physical and reactive blending composites was made by oscillatory rheological measurements. It was found that the viscosity of physical blending composites drops at lower POSS content (0.5–1 wt %) and thereafter increases with increasing POSS content; that of reactive blending composites increases with increasing POSS content and displays a solid‐like rheological behavior at low frequency region when POSS content is higher than 1 wt %. The deviation of reactive blending composites from the scaling log G′–log G″ of linear polymer in Han plot, upturning at high viscosity in Cole–Cole plot, and from van Gurp–Palmen plot are related to the gelation behavior reactively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 526–533, 2008     

Preparation and characterization of epoxy/polyhedral oligomeric silsesquioxane hybrid nanocomposites

We have prepared epoxy/polyhedral oligomeric silsesquioxane (POSS) nanocomposites by photopolymerization from octakis(glycidylsiloxy)octasilsesquioxane (OG) and diglycidyl ether of bisphenol A. We used nuclear magnetic resonance, Raman, and Fourier transform infrared spectroscopies to characterize the chemical structure of the synthetic OG. Differential scanning calorimetry and dynamic mechanical analysis (DMA) revealed that the nanocomposites possessed higher glass transition temperatures than that of the pristine epoxy resin. Furthermore, DMA indicated that all of the nanocomposites exhibited enhanced storage moduli in the rubbery state, a phenomenon that we ascribe to both the nano‐reinforcement effect of the POSS cages and the additional degree of crosslinking that resulted from the reactions between the epoxy and OG units. Thermogravimetric analysis revealed that the thermal stability of the nanocomposites was better than that of the pristine epoxy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1927–1934, 2009     

Synthesis,characterization and catalytic application of a new organometallic oligomer based on polyhedral oligomeric silsesquioxane

Although homogeneous catalysts provide high performance and selectivity, the difficulty of separation and recycling of these catalysts has bothered the scientific community worldwide. Therefore, the demand for heterogeneous catalysts that possess the advantages of homogeneous ones, with ease of separation and recyclability remains a topic of major impact. The oligomeric catalyst synthesized in this work was characterized using elemental analysis, Fourier transform infrared, ¹³C NMR, ²⁹Si NMR and energy‐dispersive X‐ray spectroscopies, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy and Brunauer–Emmett–Teller analysis and compared to its homogeneous counterpart [W(CO)₃Br₂(ATC)] in the epoxidation of 1‐octene, cyclooctene, (S )‐limonene, cis ‐3‐hexen‐1‐ol, trans ‐3‐hexen‐1‐ol and styrene. The results showed that the percentage conversion for the homogeneous species [W(CO)₃Br₂(ATC)] was slightly higher than for the oligomeric catalyst (POSS‐ATC‐[W(CO)₃Br₂]). Furthermore, the selectivity for epoxide of the oligomeric catalyst was greater than that of the homogeneous catalyst by about 25% when (S )‐limonene was used. Great conversions (yields) of products were obtained with a wide range of substrates and the catalyst was recycled many times without any substantial loss of its catalytic activity.     

Synthesis and properties of thermoplastic and dissolvable polysiloxanes containing polyhedral oligomeric silsesquioxane

There are many benefits associated with thermoplastic silicones, but very few examples exist: silicone resins or rubbers are normally thermosets. In this article, a facile and efficient approach was reported to prepare thermoplastic silicone by introducing a bulky side siloxane group. Monofunctional polyhedral oligomeric silsesquioxane (POSS), as the bulky siloxane group, was grafted onto the linear polysiloxane backbone via thiol–ene click reaction, endowing the liquid polysiloxane with thermoplastic nature. The POSS-grafted polysiloxane could be remolded by a hot-melting or solution casting process. It was worth noting that the novel thermoplastic silicone was composed of both linear siloxane main chains and siloxane side groups, which was distinctly different from previous researches on thermoplastic silicones consisted of siloxane main chains and organic side groups. Thermal analysis, rheological characterization and molecular dynamics simulation results revealed the thermoplastic properties of POSS-grafted polysiloxane depended on the bulky POSS's hindrance to the movement of the polymer backbone rather than the interaction between the organic side groups.     

Combustion and thermal properties of epoxy/phenyltrisilanol polyhedral oligomeric silsesquioxane nanocomposites

Organic–inorganic hybrid composites of epoxy and phenyltrisilanol polyhedral oligomeric silsesquioxane (Ph₇Si₇O₉(OH)₃, POSS-triol) were prepared via in situ polymerization of epoxy monomers. The nanocomposites of epoxy with POSS-triol can be prepared in the presence of metal complex latent catalyst, aluminum triacetylacetonate ([Al]) for the reaction between POSS-triol and diglycidyl ether of bisphenol A (DGEBA). The dispersion morphology of organic–inorganic hybrid was characterized by scanning electronic microscopy (SEM). The thermostability of composites was evaluated by thermal gravimetric (TG) analysis. The flammability was evaluated by cone calorimeter test. The presence of [Al] latent catalyst leads to a decrease in combustion rate with respect to epoxy and epoxy/POSS composites as well as reduction in smoke, CO and CO₂ production rate. The effect of [Al] is to reduce the size of spherical POSS particles from 3–5 μm in epoxy/POSS to 0.5 μm in epoxy/POSS[Al]. Furthermore, POSS with smaller size may form compact and continue char layer on the surface of composites more efficiently.     

Synthesis and characterization of luminescent organic-inorganic hybrid nanocomposite from polyhedral oligomeric silsesquioxane

<正>A novel polyhedral oligomeric silsesquioxane(POSS)-based organic-inorganic hybrid nanocomposite(EF-POSS) was prepared by Pt-catalyzed hydrosilylation reaction of octahydridosilsesquioxane(T_8H_8,POSS) with a luminescent substituted acetylene(2- ethynyl-7-(4-(4-methylstyryl)styryl)-9,9-dioctyl-9H-fluorene(EF)) in high yield.The hybrid nanocomposite was soluble in common solvents such as CH_2Cl_2,CHCl_3,THF and 1,4-dioxane.Its structure and property were characterized by FTIR, NMR,TGA,UV and PL,respectively.The results show that the hybrid nanocomposite with high thermal stability emits stable blue light as a result of photo excitation and possesses high photoluminescence quantum efficiency(φ_(FL)).     

Self-assembled morphologies of monotethered polyhedral oligomeric silsesquioxane nanocubes from computer simulation

Self-assembly of functionalized nanoscale building blocks is a promising strategy for "bottom-up" materials design. Recent experiments have demonstrated that the self-assembly of polyhedral oligomeric silsesquioxane (POSS) "nanocubes" functionalized with organic tethers can be utilized to synthesize novel materials with highly ordered, complex nanostructures. We have performed molecular simulations for a simplified model of monotethered POSS nanocubes to investigate systematically how the parameters that control the assembly process and the resulting equilibrium structures, including concentration, temperature, tether lengths, and solvent conditions, can be manipulated to achieve useful structures via self-assembly. We report conventional lamellar and cylindrical structures that are typically found in block copolymer and surfactant systems, including a thermotropic order-order transition, but with interesting stabilization of the lamellar phase caused by the bulkiness and cubic geometry of the POSS nanocubes.     

Morphological evolution in dewetting polystyrene/polyhedral oligomeric silsesquioxane thin film bilayers

Morphological evolution in dewetting thin film bilayers of polystyrene (PS) and a polyhedral oligomeric silsesquioxane (POSS), trisilanolphenyl-POSS (TPP), was studied as a function of annealing temperature and annealing time. The results demonstrate unique dewetting morphologies in PS/TPP bilayers at elevated temperatures that are significantly different from those typically observed in dewetting polymer/polymer bilayers. During temperature ramp studies by optical microscopy (OM) in the reflection mode, PS/TPP bilayers form cracks with a weak optical contrast at approximately 130 degrees C. The crack formation is attributed to tensile stresses within the upper TPP layer. The weak optical contrast of the cracks observed in the bilayers for annealing temperatures below approximately 160 degrees C is consistent with the cracking and dewetting of only the upper TPP layer from the underlying PS layer. The optical contrast of the morphological features is significantly enhanced at annealing temperatures of >160 degrees C. This observation suggests dewetting of both the upper TPP and the lower PS layers that results in the exposure of the silicon substrate. Upon annealing the PS/TPP bilayers at 200 degrees C in a temperature jump experiment, the upper TPP layer undergoes instantaneous cracking as observed by OM. These cracks in the upper TPP layer serve as nucleation sites for rapid dewetting and aggregation of the TPP layer, as revealed by OM and atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) results indicated that dewetting of the lower PS layer ensued for annealing times >5 min and progressed up to 90 min. For annealing times >90 min, OM, AFM, and XPS results revealed complete dewetting of both the layers with the formation of TPP encapsulated PS droplets.