Increasing Polyhedral Oligomeric Silsesquioxane Content Research Articles

Molecular Dynamics Simulation of Polyhedral Silsesquioxane Nanoparticles on Cathodes of Polymer Electrolyte Membrane Fuel Cells

The effect of octahedral cage-structured polyhedral oligomeric silsesquioxane (POSS) on the cathode catalyst layer (CCL) for polymer electrolyte membrane fuel cells (PEMFCs) is investigated via molecular dynamics simulations. A model of CCL is constructed consisting of Pt/C substrate/ionomer–POSS/water–gas. The pair correlation function analysis shows that the dense cover of ionomer chains on the Pt surface and the interaction between sulfonate groups and water molecules are weakened by POSS. At high hydration, the effective water content in the ionomer–POSS phase is drastically reduced with increasing POSS content. Interestingly, at low hydration, the effective water content is slightly improved as the POSS content increases. This water retention effect is probably due to the trapping of water molecules in the POSS cage. The diffusion coefficients of O2 and H3O+ are effectively increased. The method of inserting nanocages into ionomer can avoid the formation of a high-density ionomer film at the Pt/ionomer interface. Moreover, POSS-modified CCLs possess a self-balance of water content, thus achieving enhanced multicomponent transport involving proton, water, and oxygen transfer. It provides a strategy for designing high-performance PEMFC, particularly for fuel cell vehicles due to the self-balance property under changing humidity.

Liquid crystallinity and thermal properties of polyhedral oligomeric silsesquioxane/side-chain azobenzene hybrid copolymer

Abstract Acrylic acid-modified polyhedral oligomeric silsesquioxane (AC-POSS) was synthesized by the reaction between the amine groups in polyhedral oligomeric silsesquioxane (POSS) and acrylic acid, which could dissolve in water and can be easily purified. Free-radical copolymerization was applied to synthesize azobenzene liquid crystalline polymer silsesquioxane (LCP-POSS) with different proportions of AC-POSS and liquid crystalline monomers. The trans-isomers of azobenzene moieties in LCP-POSS were gradually transformed to cis-isomers with increasing ultraviolet irradiation time. The photoisomerization reaction of liquid crystalline polymer (LCP) and LCP-POSS showed the first-order dynamic reaction. Compared with the LCP, the photoisomerization rate constant of LCP-POSS was decreased due to the space steric hindrance of the POSS as a rigid segment. The phase transition temperature of liquid crystalline in LCP-POSS increased with increasing POSS content, and the liquid crystalline texture in LCP-POSS became smaller under the polarized light. With further increasing the POSS content (>50 wt%) in LCP-POSS, the ordered structure of the liquid crystalline phase was gradually affected, resulting in one-way liquid crystal (LC) phase behavior. The synthesized LCP-POSS has LC properties, light-responsive properties, and thermal stability. When the POSS is introduced into the LC material, the phase state of the LC material will become more abundant and the LC phase will become more stable. The significance of this study is to develop and extend its applications as stimuli-responsive materials and devices.

Polyurethane–imide–polyhedral oligomeric silsesquioxane hybrid nano-composites

In order to improve thermo-stability of polyurethane (PU), both imide group and polyhedral oligomeric silsesquioxane (POSS) were introduced into PU backbones, and PU–imide–POSS hybrid nano-composites (PUI–POSS) were synthesized with high reaction efficiency. The spherical domain formed through strong aggregation effect of POSS units, and the trend of micro-phase separation of PU was strengthened. The TDI–POSS aggregates with urethane linkage dispersed uniformly in PU matrix and maintained self-assembling ability by the formation of crystal phases with tight crystalline lamella. With increasing POSS content, the thermal degradation temperature and char yield increased, and degradation rate decreased remarkably. Moreover, the difference of degradation temperature significantly increased with degradation progressing, indicating more pronouncing thermo-stabilizing effect of POSS units at high temperature. Compared with PUI, T60% of PUI–POSS with 14.96 mass POSS increased by 270 °C. The degradation activation energy showed a large improvement, and high storage modulus can be kept with increasing temperature by introducing POSS units.

유연한 디스플레이 소자의 보호막용 직접 패턴 형성이 가능한 POSS계 저유전 물질의 제조

The passivation layer, which is located between a pixel electrode and a data elec- trode, must provide sufficiently low parasitic capacitance and sufficient electrical insulation to reduce cross talk and signal distortion. The present demand for passivation materials for next-generation displays has created interest in substitutes with low dielectric constant, high transmittance, thermal stability, and patternability; these requirements cannot be met by the silicon nitride layer and silicon dioxide used currently. To meet these requirements, negative-tone patterning systems containing polyhedral oligomeric silsesquioxane (POSS) were developed by adopting two different approaches: use of POSS in the polymeric matrix and in the crosslinker. The polymeric matrix, poly(methacryl isobutyl POSS-r- hydroxy styrene), showed improved dielectric property and thermal stability. However, the POSS content was limited owing to poor solubility. A POSS crosslinker with epoxy func- tional groups was used along with phenol group containing polymeric matrices; poly(4- hydroxy styrene). It was possible to pattern the POSS crosslinker system by irradiating it with UV light and subjecting it to subsequent thermal treatment. With increasing POSS content, the crosslinked materials showed increased transparency, higher thermal stability, and lower dielectric constant. The system could also be patterned by irradiating it with UV through a patterned mask.

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 (Tg) of the nanocomposites was significantly increased and the maximum degradation temperature (Tdmax) of nanocomposites was slightly increased compared with pure PB, implying an increase in thermal stability.

Material Properties and Reliability of Anisotropic Conductive Films (ACFs) Modified by POSS for Chip-on-Glass Assembly

This paper describes the effect of polyhedral oligomeric silsesquioxane (POSS) in anisotropic conductive films (ACFs) composition on the material properties and reliability of ACF interconnections for chip-on-glass (COG) applications. Series of POSS modified ACFs containing 0wt%, 2wt%, 4wt%, 6wt% and 8wt% contents of octa-methacrylated POSS were formulated and characterized. The POSS added in the formulations favorably affected on the materials properties of ACFs by lowering coefficient of thermal expansion (CTE) and increasing modulus (E′). In addition, an increase in the POSS contents led to higher curing density and, as a result, thermo-mechanical properties of ACFs were improved. But, the adhesion strength of ACF materials was decreased with the POSS content, due to higher modulus originated from octa-functional POSS. The reliability performances of COG assemblies using POSS modified ACFs were also investigated. In conclusion, the materials properties and module reliability of COG assemblies were improved with increasing POSS content in ACFs.

Curing dynamics and network formation of cyanate ester resin/polyhedral oligomeric silsesquioxane nanocomposites

Curing dynamics and network formation of cyanate ester resin (PT-30)/TriSilanolPhenyl polyhedral oligomeric silsesquioxane (POSS) nanocomposites were studied by means of differential scanning calorimetry (DSC), modulated temperature differential scanning calorimetry MTDSC), Fourier transform infrared (FTIR) and Raman spectroscopies. The incorporation of the POSS showed a strong catalytic effect (decrease in curing temperature and activation energy) on the curing reaction of PT-30. The activation energy of the PT-30 decreased with increasing POSS content. The most effective catalytic effect was observed at 5 wt% of the POSS. Both FTIR and Raman spectra monitored the formation of triazine (i.e. cyanurate) ring in the PT-30 and its nanocomposites with the POSS. Raman spectra revealed that the PT-30 resin preferentially reacted with –OH group in the POSS firstly to form a –O–(CNH)–O– bond, rather than react with itself to form the triazine rings, during the network formation of the PT-30/POSS nanocomposites. The strong catalytic effect of the POSS on the curing process of the PT-30 appears to be due to the formation of this –O–(CNH)–O– bond.

A solid-state NMR study of structure and segmental dynamics of poly(propylmethacryl-heptaisobutyl-pss)-co-styrene nanocomposites

The domain structure and mobility of poly(propylmethacryl-heptaisobutyl-pss)-co-styrene nanocomposites with different polyhedral oligomeric silsesquioxane (POSS) contents were investigated by various solid-state NMR techniques in combination with XRD. The NMR relaxation time measurements suggested that increasing POSS content trended to mobilize the chains in PS unit. Although XRD results showed that POSS was well dispersed into the polymer matrix, 2D WISE NMR indicated that the dispersion of POSS into the polymer matrix led to a composite structure composed of rigid and densely packed PS domain and mobile and amorphous POSS domain. This implied that the size of the two domains was very small. 2D HETCOR NMR implied that the distance between PS network and POSS unit gradually decreased when the POSS content successively increased. The dispersed POSS domain size determined by 2D spin-diffusion NMR experiments was increased with the POSS loading, being about 3.0, 3.9, 6.0 nm for the POSS15, POSS25 and POSS45 nanocomposites, respectively.

Effect of POSS on morphology and properties of poly(2,6-dimethyl-1,4-phenylene oxide)/polyamide 6 blends

Poly(2,6-dimethyl-1,4-phenylene oxide)/polyamide 6 (PPO/PA6) (50/50 w) blends filled with epoxycyclohexyl polyhedral oligomeric silsesquioxane (POSS) were prepared via melt-mixing. The reactions between POSS and PPO/PA6 blends were studied by Fourier transform infrared spectroscopy, end group and gel content tests. The morphology of PPO/PA6/POSS composites was observed by field emission scanning electron microscope and transmission electron microscope. As a chain extender and a crosslinking agent for PA6, POSS largely affected the morphology of the composites, which was mainly dependent on the melt-viscosity ratio and interfacial tension between the components. With increasing POSS content from 2 to 4 phr, the morphology of the composites transformed from droplet/matrix to co-continuous morphology. The PPO/PA6/POSS composites with co-continuous morphology had the better mechanical properties than those with droplet/matrix morphology. Dynamic mechanical thermal analysis showed that the addition of POSS increased the T g of PA6.

Preparation of polymer/POSS nanocomposites by radiation processing

Multifunctional polyhedral oligomeric silsesquioxane (POSS)-reinforced polypropylene (PP) nanocomposites were prepared by a simple and economical radiation processing, which has a great potential for the preparation of high-performance materials. The tensile strength of PP/POSS nanocomposites increased with an increasing POSS content up to 5 wt% and with an increasing absorption dose up to 50 kGy. The tensile strength of irradiated PP/POSS nanocomposites decreased at high absorption dose due to the main chain scission of PP by radiation. The PP/POSS nanocomposites showed improved thermal stability due to the formation of crosslinked network between PP and POSS by radiation.

Viscoelastic properties and residual stresses in polyhedral oligomeric silsesquioxane‐reinforced epoxy matrices

AbstractFiber‐filled thermosetting polymer composites are extensively used in aerospace industries. One disadvantage of these materials is cure induced or thermally induced residual stresses in the matrix, which may result in deteriorated performance and premature failure. This article explores the use of epoxy/multifunctional polyhedral oligomeric silsesquioxane (POSS) nanocomposites as resins with reduced thermal stress coefficients that result in mitigated residual stresses. The effect of POSS loading on the thermal stress coefficient of the epoxy/POSS nanocomposite resins was investigated from below the β‐relaxation to the α‐relaxation, or glass transition temperature, (i.e., from −100 to 180 °C) by measuring the shear modulus and linear thermal expansion coefficient. The thermal stress coefficient of the epoxy/POSS nanocomposites is found to be a strong function of temperature, decreasing rapidly with decreasing temperature through the α‐relaxation region, increasing in the vicinity of the β‐relaxation, and then decreasing below the temperature associated with the peak in the β‐relaxation. With increasing POSS content, the thermal stress coefficient is reduced compared with the neat resin in the vicinity of the α‐relaxation; however, the thermal stress coefficient increases with increasing POSS content below the temperature of the β‐relaxation peak. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2719–2732, 2008

Polyhedral oligomeric silsesquioxane-reinforced polyurethane acrylate

Hybride nanocomposite films of polyhedral oligomeric silsesquioxane (POSS) and polyurethane acrylate (PUA) were prepared by introducing POSS into PUA by free-radical photopolymerization, to enhance thermo-mechanical properties of PUA. The addition of POSS to PUA resulted in increases in the following properties: elasticity, glass transition temperature, thermal stability and dimensional stability. With increasing POSS content, the elastic modulus and thermal stability of PUA films increased due to an increased crosslinking density and the reinforcing effect of POSS particles on the PUA, whereas the surface free energies of these films decreased. The water contact angle against water increased due to the enhancement of the hydrophobicity of the polymer surface, caused by the low surface energy of POSS molecular. However, at high POSS content the mechanical properties of the films were decreased, as a result of aggregation of the POSS particles.

Preparation and characterization of styrene/styryl–polyhedral oligomeric silsesquioxane hybrid copolymers

AbstractBACKGROUND: Organic–inorganic nanocomposites were prepared by copolymerization of various monomers and polyhedral oligomeric silsesquioxane (POSS) derivatives. Preliminary results showed that styrene/styryl–POSS copolymers could be obtained using CpTiCl3 catalyst. In the work reported here, the copolymerization of styrene and styryl‐substituted POSS was studied in detail for a more effective catalyst, Cp*TiCl3.RESULTS: The glass transition temperature (Tg) of the copolymers prepared increased with increasing POSS content. The degradation temperature (Td) of the copolymers was 60 °C higher than that of syndiotactic polystyrene under nitrogen. Although the thermal properties were improved by incorporation of POSS, the catalytic activity decreased with POSS content. The racemic triad and syndiotactic index of the copolymers decreased with increasing POSS content. Gel permeation chromatograms of the copolymers exhibited multimodal distribution due to the presence of multi‐active centres, which were formed by interaction of Ti with the POSS siloxane linkage.CONCLUSION: With the incorporation of POSS, the thermal properties of polystyrene were improved. The styrene/styryl–POSS copolymers are formed through the various active sites arising from the interactions of Ti with POSS. Copyright © 2008 Society of Chemical Industry

Preparation and properties of POSS grafted polypropylene by reactive blending

The octavinyl polyhedral oligomeric silsesquioxane (POSS) grafted polypropylene (PP) was first prepared by reactive blending. The structure and properties of physical blending and reactive blending composites of PP/POSS were investigated by wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA). WAXD analysis shows that the POSS in the reactive blending composites has better compatibility with PP than in the physical blending composites. The β-form crystalline hence disappears even the non-reactive POSS can act as an effective β-nucleating agents. DSC analysis shows the reactive blending composites have higher crystalline temperature while POSS in the physical blending composites have little effect on the crystalline temperature. The modulus of reactive blending composites increases in the presence of POSS, while that of the physical blending composites decreases with increasing POSS content.

Rheological behavior of polypropylene/octavinyl polyhedral oligomeric silsesquioxane composites

AbstractThe 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

In‐situ Synthesis and Characterization of Polyamide 6/POSS Nanocomposites

AbstractThe nanocomposites of polyamide 6 (PA6) and polyhedral oligomeric silsesquioxane (POSS) containing primary and secondary amino groups were synthesized through in‐situ polymerization. The chemical structure of the PA6/POSS nanocomposites was characterized with FT‐IR and 1H‐NMR spectroscopies. The solution viscosity results showed the increase in intrinsic viscosity with increasing POSS loadings. The random positioning of the POSS molecules in PA6 chain was confirmed by x‐ray diffraction studies. The gradual decrease in the melting point and crystallization temperature with increasing POSS content was observed by the differential scanning calorimetry. The thermogravimetric analysis results showed that the POSS incorporation does not enhance the thermal resistance of PA6/POSS nanocomposites.

Hybrid Styryl-Based Polyhedral Oligomeric Silsesquioxane (Poss) Polymers

The authors have taken a unique approach to the synthesis and study of hybrid organic/inorganic materials. The method involves synthesizing nano-size inorganic P{sub 1}R{sub 7}Si{sub 8}O{sub 12} clusters which contain seven inert R groups for solubility and only one functional P group for polymerization. This strategy permits the synthesis of melt processable, linear hybrid polymers containing pendent inorganic clusters and allows one to study the effect these clusters have on chain motions and polymer properties. The synthesis of styrene-based polyhedral oligomeric silsesquioxane (POSS) macromers, their free radical homopolymerization and copolymerizations with varying amounts of 4-methylstyrene, and analysis of the effect of the pendent POSS group is presented. All of these polymers decompose under nitrogen between 365 and 400 C, and the glass transitions for these materials vary from around 110 C up to the decomposition point. Both T{sub dec} and T{sub g} increase with increasing POSS content. The shorter the spacer unit between the POSS group and the polymer chain the higher the T{sub g}. Interestingly, a slight change in the inert R groups on the POSS cluster has a large effect on the glass transition indicating that POSS-POSS interactions have an effect on chain mobility.