Polyhedral Oligomeric Silsesquioxane Filler Research Articles

Rationalizing the Composition Dependence of Glass Transition Temperatures in Amorphous Polymer/POSS Composites.

We report that the fractions of "bonded" or "unbonded" monomers at a filler interface dictate the composition dependence of the glass transition temperatures (Tg) of polyhedral oligomeric silsesquioxane (POSS)-containing nanocomposites. Tg is arguably the single most important material property; however, predicting Tg in nanocomposites is often challenging because of confounding interfacial effects. To this end, we design a model nanocomposite to systematically study Tg of nanocomposites by leveraging the "all-interfacial" nature of ultrasmall POSS fillers loaded into random copolymers of styrene and 2-vinylpyridine (2VP). The amine-functionalized POSS forms hydrogen bonds only with 2VP, which behaves as a "bonded" monomer. The influence of copolymer composition and POSS loading on the Tg of this model composite is successfully explained by a Fox equation framework. This model also captures the Tg increase of other POSS-based polymer composites and potentially directs the future design of nanocomposite materials with tailored Tg.

In situ implantation of cross-linked functional POSS blocks in Nafion® for high performance direct methanol fuel cells

Polyhedral oligomeric silsesquioxane (POSS) has attracted increasing attention because of its organic/inorganic, nanosize, easily functional nature, especially in the applications of direct methanol fuel cells (DMFCs). In this work, we have successfully synthesized a novel bifunctional POSS (Vi-POSS-SO3Na) with vinyl and sulfonic acid groups by thiol-ene click reaction. Vi-POSS-SO3Na was introduced into Nafion® matrix and cross-linked by in-situ simply thermal treatment. The implantation of the bifunctional POSS filler gives significant improvements in the performance of such proton exchange membranes (PEMs). The cross-linked hybrid membrane with 12 wt% of Vi-POSS-SO3Na (X-Nafion@POSS-12) has a high proton conductivity (121 mS cm−1) at 80 °C, excellent dimensional stability and the lowest methanol permeability (5.4 × 10−8 cm2 s−1). The highest power density of the DMFCs was obtained by using the X-Nafion@POSS-12 as PEM in DMFC at 80 °C, and its value (34.93 mW cm−2) is twice higher than that of Nafion 212 membrane (14.90 mW cm−2). The novel in-situ fabrication method gives a simple and potential approach for the preparation of PEMs used in DMFCs.

Enhanced Electrochromic Performances of Polyhedral Oligomeric Silsesquioxane (POSS) Modified Viologen Derivatives

Polyhedral oligomeric silsesquioxane (POSS) is an inorganic silica nanocage surrounded by organic functional groups. Due to the presence of organic peripheries around the rigid case, functionalized POSS has often exhibited outstanding properties, thus finding useful for constructing porous inorganic-organic hybrid networks.The electrochromic devices (ECDs) offer noticeable color changes due to the electron transfer and redox reaction. The electrochromic materials play a critical role in determining the optical response and absorption intensity of the ECDs. Various electrochromic materials have been investigated, including inorganic metal oxides, viologens, and conducting polymers. Among these, viologen derivatives have been studied in depth owing to high electron-accepting capability and facile synthetic routes. Besides, viologen based ECDs have found various applications, such as smart windows, electronic paper, and the famous antiglare rearview mirrors developed by Gentex. However, critical weaknesses of viologens include low coloration efficiency, slow switching speed, and reduced long-term stability. Furthermore, the durability in the repeated operation of ECDs is limited in non-complementary device structures.Herein, we present the modification of viologen derivatives with the incorporation of POSS, in which the structural rigidity of POSS fillers and the synthetic versatility of viologen compounds are combined to ensure improved electrochromic performances. The solid-state ECDs are fabricated by sandwiching the single-layered ion gel containing POSS-modified viologens between two transparent electrodes. The resulting electrochromic behaviors are compared with those of conventional viologens, in terms of cyclic voltammetry, spectroelectrochemistry, and kinetic stability. Furthermore, the preparation of flexible ECDs using silver nanowire-PEDOT:PSS composite electrode is presented, and stable electrochromic operation in the repeated redox transitions is demonstrated on various plastic substrates.

Molecular fillers for increasing the refractive index of polystyrene hybrids by chain assembly at polyhedral oligomeric silsesquioxane

We developed a molecular filler based on polyhedral oligomeric silsesquioxane (POSS) containing halogenated aromatic substituents to increase the refractive indices (RIs) of polystyrene (PS). PS hybrid films with a series of POSS derivatives were prepared through the solution method, and RI measurements were performed. Accordingly, it was revealed that these halogenated POSS fillers can increase the RI of the films. In particular, the degree of increase was larger than those estimated by theoretical prediction, suggesting that the accumulation of polymer chains around the POSS filler plays a key role in the increasing effect. In addition, it was shown that critical losses of thermal and mechanical properties were barely observed by adding POSS fillers. Preparation without the conventional sol‒gel method for the single-molecule-type filler with high-RI polymer hybrids based on chain assembly can be demonstrated. The halogenated polyhedral oligomeric silsesquioxane (POSS) fillers can increase the refractive indices (RIs) of the films. In particular, the degree of increases was larger than those estimated by the theoretical prediction, suggesting that accumulation of polymer chains around the POSS filler plays a key role in the increasing effect. Moreover, critical losses of thermal and mechanical properties were hardly observed. Preparation without the conventional sol‒gel method for the single-molecule-type filler with high-RI polymer hybrids based on the chain assembling can be demonstrated.

Fluoroalkyl POSS with Dual Functional Groups as a Molecular Filler for Lowering Refractive Indices and Improving Thermomechanical Properties of PMMA.

The dual-functionalized polyhedral oligomeric silsesquioxane (POSS) derivatives, which have the seven fluorinated alkanes and the single acrylate ester on the silica cube, were designed as a filler for lowering the refractive index (RI) and improving thermomechanical properties in poly(methyl methacrylate) (PMMA). The desired dual-functionalized POSS fillers were prepared, and because of its high miscibility, homogeneous films were readily obtained, by the casting method, with the mixture solutions containing the modified POSS and the polymers. From optical measurements, it was found that the larger effects of lowering the RIs of the PMMA matrices were observed from the modified POSS than those of the octa-substituted POSS derivatives with the homogeneous substituents. It should be mentioned that the degradation temperatures and the storage moduli were able to be greatly elevated by loading the present POSS fillers. Finally, it was demonstrated that the methacrylate ester-tethered POSS should be the most effective filler for modulating PMMA (Δn = −0.020, ΔTd20 = +53 °C, ΔE’/E’ = +72%).

Enhanced PIM-1 membrane gas separation selectivity through efficient dispersion of functionalized POSS fillers

Polyhedral oligomeric silsesquioxane (POSS) are silica based nano-fillers with tunable functionality, nanometric cage structure and are promising fillers for generating high-performance mixed matrix membranes (MMMS) for gas separation processes. Here, we report highly permeable and selective MMMs fabricated from the polymer of intrinsic microporosity (PIM-1) filled with functionalized and unfunctionalized octaphenyl substituted POSS particles. Amine and nitro functionalized POSS particles (OAPS and ONPS) showed greater dispersibility in PIM-1 solution compared to unfunctionalized POSS (OPS). The OPS MMMs showed an increase in single and mixed gas (CO2: N2 and CO2: CH4, 50:50vol%) permeability and a decrease in selectivity. In contrast the OAPS MMMs showed significantly enhanced selectivity for air-oxygen and hydrogen-natural gas mixed gases with minimal changes in permeability. Higher loadings led to reduced permeability but significantly enhanced selectivity (~200%). The physical aging behavior of nanometric level dispersed MMMs in thick (~70µm) and thin film configurations (~2.5µm and ~200nm), showed that the addition of POSS-based particles could delay the rate of aging. We could directly correlate the enhanced performances to both an increase in mechanical rigidity of the membrane, as well as an enhanced degree of interfacial hydrogen bonding for amine functionalized POSS fillers.

POSS-based molecular fillers for simultaneously enhancing thermal and viscoelasticity of poly(methyl methacrylate) films

It was previously shown that polyhedral oligomeric silsesquioxane (POSS)-based molecular fillers can enhance the mechanical properties of polymer matrices as a viscoelastic material. However, POSS fillers hardly affected the initial pyrolysis step. Therefore, it was still challenging to reinforce thermal durability of polymers. This manuscript demonstrates development of molecular fillers for simultaneously enhancing decomposition temperature and both storage (E′) and loss (E″) moduli. The series of molecular fillers based on POSS having various functional groups to make an interaction with poly(methyl methacrylate) (PMMA) matrices were designed and synthesized. Initially, the single and multiple reactive units as methacrylate ester to form covalent bonds with PMMA were introduced into octaisobutyl POSS (iBu-POSS). It was proposed that cross-linking reactions with polymer chains proceeded after annealing at 65°C. Then, significant enhancements of both E′ and E″ were observed. To obtain further enhancements especially for thermal stability, the POSS fillers of second generation having amine and 1,2-diol groups, which were expected to make strong interaction with the side chains in PMMA, were designed and loaded into polymer matrices. From the series of measurements with the homogeneous film samples containing POSS fillers, it was presented that all modified POSS derivatives can greatly improve thermal stability and mechanical properties as we expected.

Synthesis of POSS Derivatives Having Dual Types of Alkyl Substituents and Their Application as a Molecular Filler for Low-Refractive and Highly Durable Materials

Abstract The preparation of polyhedral oligomeric silsesquioxane (POSS) derivatives possessing different types of alkyl substituents and their application as a molecular filler for simultaneously lowering refractive indices and enhancing thermal and mechanical properties of poly(methyl methacrylate) (PMMA) are described. The modified POSS derivatives were prepared in situ through sol–gel reactions in the presence of two types of alkylsilanes. The products had molecular distributions originating from the formation of cubic and pentagonal prism structures and variable introduction ratios of alkyl substituents. Owing to the reduction of symmetry, the POSS fillers showed high miscibility with PMMA. From optical and thermal measurements, it was demonstrated that the POSS fillers with dual types of substituents can lower refractive indices (RIs) of PMMA matrices and enhance thermal and mechanical properties.

Remarkably high miscibility of octa-substituted POSS with commodity conjugated polymers and molecular fillers for the improvement of homogeneities of polymer matrices

This manuscript describes the extremely high affinities of polyhedral oligomeric silsesquioxane (POSS) with conjugated polymers. Polymer films of polyfluorene (PF) and poly(3-hexylthiophene) (P3HT) containing a series of octa-substituted POSS at variable concentrations were prepared. The relationships between the thermal and optical properties of commodity-conjugated polymers and the chemical structures of the substituents in POSS were evaluated by a series of experiments. It was shown that the POSS fillers with relatively longer alkyl substituents can enhance the thermal stabilities of the polymer matrices, even though most of the POSS fillers reduced the decomposition temperatures. The UV−Vis absorption measurements showed that the narrower absorption bands were obtained from the POSS-containing film with PF. It was suggested that the aggregation of the polymer chains could be suppressed by the POSS filler, leading to highly homogeneous states in the films. Moreover, for the P3HT films, the extension of the main-chain conjugation was induced by the POSS fillers with shorter alkyl substituents via the suppression of intermolecular interactions among the polymer chains. These data mean that the POSS fillers can have a significant role in the improvement of the homogeneity in the polymer films due to their high affinity to the conjugated systems. Cubic silsesquioxanes (POSS) with various alkyl substituents were loaded onto commodity-conjugated polymers such as polyfluorene and poly(3-hexylthiophene-2,5-diyl) to investigate structure-property relationships between the substituents of POSS fillers and properties of the polymer films. It was found that the series of POSS fillers can be introduced into conjugated polymer films with high concentrations. Owing to high miscibility, it was demonstrated that POSS can work as a superior molecular filler for realizing homogeneous amorphous films with high thermal stability based on conjugated polymers.

Synthesis of sulfonic acid-containing POSS and its filler effects for enhancing thermal stabilities and lowering melting temperatures of ionic liquids

To improve the thermal stability and lower the melting temperature of ion salts for using as ionic liquids (ILs), we designed an efficient filler based on octa-substituted polyhedral oligomeric silsesquioxane (POSS). Accordingly, the sulfonic acid-presenting POSS showed superior properties as a filler for improving thermal properties of ILs. In this report, initially the synthetic procedure for the sulfonic acid POSS is illustrated. We found that the POSS filler has good dispersibility in the ion salts, providing the series of homogeneous mixtures with various types of ion salts or ILs. Next, it is indicated that the degradation temperatures of the ion salts were significantly elevated by adding the POSS filler. Moreover, lowering effects on the melting temperatures were observed. In particular, we can demonstrate the transformation of ion salts to ILs by mixing with a small amount of the POSS filler. The data on the thermodynamic parameters during the melting process suggest that the symmetrical structure of the silica cube and the disturbance of the crystalline formation by POSS should contribute to the modulation of thermal properties of the ion salts.

Rational design of polyhedral oligomeric silsesquioxane fillers for simultaneous improvements of thermomechanical properties and lowering refractive indices of polymer films

ABSTRACTWe describe here the design and synthesis of the polyhedral oligomeric silsesquioxane (POSS)‐based dual‐functional molecular fillers for simultaneously lowering refractive indices and improving thermomechanical properties of conventional polymers. We prepared the composite films with poly(methyl methacrylate) and polystyrene containing the series of the POSS derivatives with the single functional unit for interacting with polymer chains and heptacyclopentyl substituents for creating exclusive volumes around the POSS core. From the measurements of refractive indices of polymer composites, it was revealed that all POSS fillers can lower the refractive index of the films. In addition, thermal stabilities and mechanical properties were enhanced by adding POSS fillers. The filler effect on the thermal properties can be explained by the structural features of POSS: The highly symmetrical structure of the silica cube should suppress thermal motions, resulting in the large enhancement of thermomechanical properties of polymer matrices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3583–3589

POSS 기반 유-무기 하이브리드 충전제와 폴리아미드계 TPE로 이루어진 나노복합체의 제조 및 특성

아민 작용기를 가진 POSS에 toluene diisocyanate(TDI)와 caprolactam(CL)의 반응물을 반응시켜 POSS 기반의 하이브리드 충전제(POSS-(TDI+CL))를 합성하였고 이를 상업용 폴리아미드계 열가소성 탄성체인 PA-TPE에 블렌딩하여 PA-TPE/POSS-(TDI+CL) 복합체를 제조하였다. POSS계 충전제의 화학구조는 FTIR과 <TEX>$^1H$</TEX> NMR을 사용하여 확인하였다. PA-TPE/POSS-(TDI+CL) 복합체는 충전제를 PA-TPE에 7 wt%까지 첨가하여 제조하였고 이들은 순수 PA-TPE와 변성되지 되지 않은 PA-TPE/octaphenyl POSS의 복합체보다 낮은 tension set 값을 보여 탄성회복력이 향상되었다. 또한 하이브리드 충전제의 함량이 증가함에 따라 인장강도와 모듈러스가 증가하였다. 결론적으로 하이브리드 충전제인 POSS-(TDI+CL)는 원래 PA-TPE의 탄성에 나쁜 영향을 미치지 않고도 기계적 물성을 향상시킬 수 있는 적절한 충전제라 볼 수 있다. Commercially available polyamide thermoplastic elastomer (PA-TPE) was blended with hybrid filler which was prepared by means of the reaction between polyhedral oligomeric silsesquioxane (POSS) containing amine group and toluene diisocyanate (TDI)-caprolactam (CL) to explore the effect of blending the hybrid filler with the TPE. The chemical structure of the filler was identified by using FTIR and <TEX>$^1H$</TEX> NMR. The composites, PA-TPE/POSS-(TDI+CL), which were the blends of TDI+CL modified POSS filler and PA-TPE up to 7 wt%, showed better elastic recovery delivered from lower tension setting compared to the PA-TPE and the PA-TPE/octaphenyl POSS blend. In addition the tensile strength and the initial modulus increased with increasing the hybrid filled content. Consequently it was assumed that the POSS-(TDI+CL) filler was a suitable material for enhancing strength and modulus without loss of elastic properties for the original PA-TPE.

POSS fillers for modulating the thermal properties of ionic liquids

We report a polyhedral oligomeric silsesquioxane (POSS)-based filler for improving the thermal properties of ionic liquids (ILs). We prepared homogeneous mixtures containing the octa-substituted carboxy-POSS as a filler via a solution process. Initially, it was found that the melting temperatures of the ionic pairs were lowered by adding the POSS filler. Based on this effect, some of ionic salts were transformed into ILs by adding the POSS filler. Reinforcement of thermal stability was also observed from the salts which have an intrinsically low decomposition temperature. According to the thermodynamic parameters in melting, the introduction of the POSS filler significantly reduces both the fusion enthalpy and entropy. Furthermore, from experiments on the substituent effect on POSS, it was found that only octa-carboxy POSS had an effect on the modulation of the thermal properties of ion salts. Considering these results, we summarized that the highly symmetrical rigid structure of the silica cage could be responsible for the improvement of the thermal properties of the ion salt matrices via the strong interaction between the carboxyl groups and the ion salt matrices. Our concept is feasible not only for the conversion of conventional ionic salts into ILs, but also for the development of new series of ILs.

Phenolic resin–trisilanolphenyl polyhedral oligomeric silsesquioxane (POSS) hybrid nanocomposites: Structure and properties

The structure and properties of organic–inorganic hybrid nanocomposites prepared from a resole phenolic resin and a POSS mixture containing >95 wt% trisilanolphenyl POSS was investigated by POM (polarized optical microscopy), SEM, TEM, WAXD, FT-IR, DSC, and TGA techniques. Composites with 1.0–10.4 wt% of POSS were prepared by dissolving the POSS and the phenolic resin into THF, followed by solvent removal and curing. Both nano- and micro-sized POSS filler aggregates and particles were shown to be heterogeneously dispersed in the cured matrix by POM, TEM, SEM, and X-EDS. POSS was found everywhere, including in both dispersed phase domains and in the matrix. The nanocomposite morphology appears to form by a multi-step POSS aggregation during the process of phase separation. Both the matrix and dispersed ‘particulate’ phase domains are mixtures of phenolic resin and POSS. POSS micro-crystals act as the core of the dispersed phase. The bigger dispersed domains consist of smaller particles or aggregates of POSS molecules that exhibit some order but regions of matrix resin are interspersed. A WAXD peak at 2 θ∼7.3° indicates crystalline order in the POSS aggregates. This characteristic peak's intensity increases with an increase in POSS loading, suggesting that more POSS molecules have aggregated or crystallized. FT-IR spectra confirm that hydrogen bonding exists between the phenolic resin and POSS Si–OH groups. This increases their mutual compatibility, but H-bonding does not prevent POSS aggregation and phase separation during curing. TGA measurements in air confirmed the temperature for 5% mass loss in increases with increase of POSS loading and at T>550° the thermal stability increases more sharply with POSS loading. The nanocomposite glass transition temperatures ( T g) are only slightly be affected by the POSS filler.