Polyhedral Oligomeric Silsesquioxane Cages Research Articles

Properties of POSS/HNBR Elastomer Nanocomposites

A series of composite materials containing polyhedral oligomeric silsesquioxanes (POSS) and hydrogenated butadiene-acrylonitrile rubber (HNBR) were prepared. The goal of the work was to evaluate the effect of the type and reactivity of functional groups in the POSS cage on properties of the resulting elastomeric nanocomposites. The paper presents some of the preliminary results obtained from the studies. The results indicate that incorporation of POSS into silica-filled HNBR elastomer network increases interfacial interactions of the systems and the POSS molecules can be successfully used as coagents of crosslinking towards the elastomer matrix and efficient additives improving the mechanical properties of elastomeric nanocomposites. Furthermore, evaluation of changes in mechanical properties, induced in a result of POSS/HNBR composites ageing, show that the inclusion of POSS in the HNBR network is directly influencing the stabilizing effect and improves the ageing resistance of elastomer composites.

Synthesis and characterization of three kinds of bifunctionalized polyhedral oligomeric silsesquioxanes with the same cage structure

A facile, single-step synthetic pathway leading to bifunctionalized polyhedral oligomeric silsesquioxanes (POSS) with two different reactive functional groups attached to the same cage structure, namely Vi-Cl POSS, is reported in this paper. The Vi-Cl POSS were synthesized through the cohydrolysis and cocondensation of (3-chloropropyl)trimethoxysilane, vinyltrimethoxysilane and propyltrimethoxysilane in ethanol media under acidic conditions, the number of vinyls and chloropropyls which attached to cage structure can be controlled by the monomers feed ratio of three kinds of trialk-oxysilanes. In this method, three different bifunctional polyhedral oligomeric silsesquioxanes were synthesized, including [Si8O12 (CH=CH2)(C3H6Cl)2(C3H7)5] (POSS1), [Si8O12(CH=CH2)2(C3H6Cl)(C3H7)5] (POSS2) and [Si8O12(CH=CH2)(C3H6Cl)(C3H7)6] (POSS3). Due to the reactive functional groups attached to the cage, these specific bifunctional polyhedral oligomeric silsesquioxanes can be copolymerized with other organic monomers by free radical polymerization, hydrosilylation reactions and atom transfer radical polymerization to obtain organic–inorganic hybrid nanocomposites, respectively. The outstanding advantage of cohydrolysis–cocondensation routes is that the substitution pattern of different substituents around the POSS cage can be precisely controlled.

Tandem mass spectrometry of electrosprayed polyhedral oligomeric silsesquioxane compounds with different substituents

Polyhedral oligomeric silsesquioxanes (POSSs), defined as [RSiO(3/2) ](n) with R designating an organic substituent, were considered here as models of highly cross-linked polysiloxanes, to be further used as references in tandem mass spectrometric characterization of plasma polymers of hexamethyldisiloxane, expected to be composed of organic polydimethylsiloxane (PDMS) and inorganic (SiO(x) ) silica-based parts. The collision-induced dissociation (CID) behavior of [RSiO(3/2) ](8) compounds was then studied as a function of the R substituent. POSS compounds were produced in the gas phase as ammonium adducts and the product ions generated upon CID, amongst which was the protonated precursor, were accurately mass measured in an orthogonal acceleration time-of-flight mass analyzer. The presence of eight propylamine substituents was shown to induce sequential dehydration of the protonated precursor, ultimately leading to a complete unfolding of the POSS cage. Similar opening of the octahedron structure in the protonated molecule substituted with OSi(CH(3) )(3) , OSiH(CH(3) )(2) or OH (formed upon methanolysis of dimethylsiloxy substituents) was proposed to account for the product ions generated during their CID. Sequential charge-remote transfers of a methyl group (and of H in the case of dimethylsiloxy substituents) from one substituent group to a neighboring one was shown to lead to a linear co-oligomeric chain composed of randomly distributed siloxy-based monomers. All the peaks observed in CID could be accounted for by applying dissociation reactions typically occurring in protonated polysiloxane-like oligomers. The large number of product ions observed in MS/MS was found to result from the variety of possible structural rearrangements, producing numerous linear isomeric forms of the dissociating species.

Nanostructured hyperbranched polyurethane elastomer hybrids that incorporate polyhedral oligosilsesquioxane

Novel thermoplastic hyperbranched polyurethane (HBP) elastomer hybrids containing polyhedral oligomeric silsesquioxane (POSS) have been synthesized using an A2+B3 approach. Different compositions of these hybrid nanomaterials were obtained from reactions of POSS-diol, triethanolamine, poly(ε-caprolactone)diol, and 4,4′-methylenebis(phenyl isocyanate) with a chain extender. The covalent attachment of POSS molecules to the backbone of the polyurethane chain was characterized with FT-IR and NMR spectroscopies. The non-agglomerated homogeneous dispersion obtained through the covalent attachment of POSS molecules and the HBP matrix was observed by SEM imaging. The mechanical properties, including the tensile and yield strengths, Young’s modulus, and toughness, significantly increased after the introduction of POSS molecules into the hybrids; this increase can be ascribed to the nano-reinforcement effect of the POSS cages and the long-range branched structure of the polymer. Thermogravimetric analyses indicated that the thermal stability of the polymer matrix was improved by the introduction of a small amount of POSS.

A novel stable and efficient light-emitting solid based on saponite and luminescent POSS

A novel hybrid organic/inorganic clay prepared by intercalation of a luminescent polyhedral oligomeric silsesquioxane (POSS) in a nanosized synthetic saponite clay was synthesized and characterized by a multidisciplinary approach including XRD, HRTEM, TGA and UV-Vis and photoluminescence spectroscopies. The luminescent POSS was obtained by linking a cyanine (IRIS3COOH) on the POSS cage functionalized with two amino groups (sample named IRIS3-POSS-NH2). One of the amino groups served for the inclusion in the saponite interlayer space. The final hybrid material (IRIS3-POSS-NH3/SAP), characterized by high quantum efficiency and improved thermal and photochemical stability with respect to the pure luminescent POSS and dye, was successfully tested as the luminescent layer in a hybrid light emitting diode (HLED) device.

Dimethacrylic/epoxy interpenetrating polymer networks including octafunctional POSS

This investigation presents the synthesis of simultaneous interpenetrating polymer networks based on dimethacrylic/epoxy resins with or without polyhedral oligomeric silsesquioxane (POSS) via in situ polymerization. The curing behavior was studied using differential scanning calorimetry (DSC). The influence of the organic groups from the POSS cages on the curing kinetics of the IPNs was also studied by FT-IR spectrometry. The homogeneous phase structure of the cured IPN was proved by DMA tests. Additionally the integrity of the IPN was also demonstrated by thermal decomposition which occurs in one single step.

Synthesis and characterization of polyimide/polyhedral oligomeric silsesquioxane nanocomposites containing quinolyl moiety

AbstractA series of functional polyhedral oligomeric silsesquioxane (POSS)/polyimide (PI) nanocomposites were prepared using a two‐step approach. First, octa(aminophenyl)silsesquioxane (OAPS) was mixed with poly(amic acid) (PAA) prepared by reacting bis(4‐amino‐3,5‐dimethylphenyl)‐3‐quinolylmethane and 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride. Second, the resulting solution was subjected to thermal imidization. The well‐defined ‘hard particles’ (POSS) and the strong covalent bonds in the amide linkage between the carbon atom of the carboxyl side group in PAA and the nitrogen atom of the amino group in POSS lead to a significant improvement in the thermal and mechanical properties. Homogeneous dispersion of POSS cages in the PI is evident from scanning electron microscopy, which further confirms that the POSS molecule becomes an integral part of the organic‐inorganic inter‐crosslinked network system. Differential scanning calorimetry and dynamic mechanical analysis show that the glass transition temperatures of the POSS‐containing nanocomposites are higher than that of the corresponding neat PI system, owing to the significant increase of the crosslinking density in the PI/POSS nanocomposites. Increasing the concentration of OAPS in the PI networks decreases the dielectric constant. Pure PI and PI/POSS systems have good antimicrobial activity. Copyright © 2011 Society of Chemical Industry

Polyhedral oligomeric silsesquioxane‐based fluoroether‐containing terpolymers: Synthesis, characterization and their water and oil repellency evaluation for cotton fabric

AbstractA series of polyhedral oligomeric silsesquioxane (POSS) based hybrid copolymers poly(POSS‐co‐methyl methacrylate −co‐ 4‐vinylbenzyl fluoroether carboxylate) (P(POSS‐MMA‐VBFC)) were prepared via radical polymerization and characterized by nuclear magnetic resonance, fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, gel permeation chromatography, X‐ray powder diffraction, scanning electron microscopy and transmission electron microscopy. The thermal properties of these polymers (Td > 250 °C) were improved by the introduction of POSS cage. The cotton fabrics coated with the polymers possessed excellent water and oil repellency. The water and salad oil contact angle could be achieved from 133° to 159° and from 127° to 141° respectively as the content of POSS in the polymer increased from 0 to 7.1 wt %. Moreover, the cotton fabric coated with the terpolymer was less flammable than the uncoated one. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Polyetheramine–polyhedral oligomeric silsesquioxane organic–inorganic hybrid membranes for CO 2/H 2 and CO 2/N 2 separation

In this study, composite polyetheramine (PEA)–polyhedral oligomeric silsesquioxane (POSS) membranes were successfully fabricated for carbon dioxide/hydrogen (CO 2/H 2) and carbon/nitrogen (CO 2/N 2) separation. The organic functional groups on the POSS cage and its small particle size enhanced its compatibility with PEA. With the optimized conditions for membrane fabrication, a uniform distribution of POSS particles across the membranes could be observed from the SEM–EDX analysis. With the weight ratio of PEA:POSS 50:50, the crystallinity of the membranes is significantly suppressed as observed in the reduction of the melting point to 2.6 °C, compared with the original PEA melting point of 37.4 °C. In addition, the mechanical strength of the soft PEA is enhanced. A high CO 2 permeability of 380 Barrer with a moderate CO 2/N 2 selectivity of 39.1 and a CO 2/H 2 selectivity of 7.0 are achieved at 35 °C and 1 bar for PEA:POSS 50:50 membrane. The relationship between gas transport properties and membrane composition is elucidated in terms of PEA/gas interaction and nanohybrid structure. Fundamental study on the effect of temperature and pressure on the performance of the membranes were also carried out. The gas permeability through the membrane is found to increase at the expense of selectivity with the increase in temperature. At higher upstream gas pressure during permeation tests, improvements are observed in both CO 2 permeability and ideal CO 2/H 2 and CO 2/N 2 selectivity due to the plasticization effect of CO 2. The CO 2/N 2 selectivity of the membrane is found to decrease considerably under the binary mixture because of competitive sorption between CO 2 and N 2 in the membranes.

Hydrogen Bond Assisted Assembly of Well-Ordered Polyhedral Oligomeric Silsesquioxane–Block Copolymer Composites

Well-ordered block copolymer nanocomposites with d-spacings as small as 15 nm and additive loadings greater than 70 mass % were formed upon blending functionalized polyhedral oligomeric silsesquioxanes (POSS) additives into disordered block copolymers containing poly(ethylene oxide) (PEO) as one of the blocks. The POSS additives were functionalized with maleamic acid or aminophenyl groups as ligands to enable selective hydrogen bonding with the PEO chains. The selective interaction of the additives with the PEO chains caused microphase separation of the block copolymer leading to formation of well-ordered morphologies as evidenced by small-angle X-ray scattering. Further addition of the additive induced transitions between cylindrical and spherical morphologies. While both ligands induced order, the maleamic acid ligand enabled higher levels of incorporation of POSS cages into the PEO phases of the composite. Differential scanning calorimetry and wide-angle X-ray diffraction were performed to confirm compatibility and good mixing of the additives within the PEO phase. The maleamic ligands can be cross-linked by a thermal treatment. The cross-linking was used to stabilize the structure of the composites prior to calcination at high temperatures, which resulted in the formation of mesoporous silica. Transmission electron microscopy showed that the cylindrical and spherical morphologies of the parent composites were maintained in the mesoporous silica.

Breaking Symmetry toward Nonspherical Janus Particles Based on Polyhedral Oligomeric Silsesquioxanes: Molecular Design, “Click” Synthesis, and Hierarchical Structure

The design, synthesis, and self-assembly of a series of precisely defined, nonspherical, polyhedral oligomeric silsesquioxane (POSS)-based molecular Janus particles are reported. The synthesis aims to fulfill the "click" philosophy by using thiol-ene chemistry to efficiently install versatile functionalities on one of the POSS cages. In such a way, both the geometrical and chemical symmetries were broken to create the Janus feature. These particles self-organize into hierarchically ordered supramolecular structures in the bulk. For example, the Janus particle with isobutyl groups on one POSS and carboxylic groups on the other self-assembles into a bilayered structure with head-to-head, tail-to-tail arrangements of each particle, which further organize into a three-dimensional orthorhombic lattice. While the ordered structure in the layers was lost upon heating via a first-order transition, the bilayered structure persisted throughout. This study provides a model system of well-defined molecular Janus particles for the general understanding of their self-assembly and hierarchical structure formation in the condensed state.

Catalytic and reinforcing effects of polyhedral oligomeric silsesquioxane (POSS)-imidazolium modified clay in an anhydride-cured epoxy

In this article, we report novel epoxy-based hybrids prepared via incorporating 1,2-dimethyl-3-(benzyl-heptaisobutyl-POSS) imidazolium chloride (POSS-IMC) and POSS-IMC-modified clay (POSS-MMT) into the resin based on 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate (ECHM) and hexahydrophthalic anhydride (HHPA). We demonstrate that both POSS-IMC and POSS-MMT can reduce the cure temperature of the epoxy/anhydride system, and the catalyzing effect involves chemical reactions between POSS-IMC and ECHM/HHPA, which may lead to the attachment of POSS cages at chain ends. The incorporation of the POSS-IMC, free and ionically bonded in clay, gives rise to dissimilar morphologies that affect the thermo–mechanical properties of the hybrids. The ECHM/HHPA/POSS-IMC resin exhibits a slight improvement in glassy modulus as compared with the neat ECHM/HHPA resin, which is attributed to the formation of sub-micron and nano-sized POSS domains that act as physical cross-link points hindering polymer chain motions. The much enhanced reinforcing effect of POSS-MMT is ascribed to the effective stress transfer between the matrix and clay layers that may originate from the strong interactions between the pendent POSS in the network and POSS attached to the clay surfaces. Reduction in coefficient of thermal expansion (CTE) was also found for the hybrids.

Low temperature direct imprint of polyhedral oligomeric silsesquioxane (POSS) resist

In this paper we present results on the synthesis of a hybrid organic/inorganic resist based on polyhedral oligomeric silsesquioxane cages and used it in a thermal nanoimprint lithography process. Our resist has been developed in order to be uniformly spin coated on silicon substrates, imprinted at a reduced temperature (40°C), then cross-linked first at elevated temperatures (>120°C) during the imprinting process and then by exposure to UV radiation outside the imprinting tool. With this process, a low shrinkage rate of the resist is achieved after cross-linking, combined with high mechanical and thermal properties.

The Influence of the Organic Substituents from the Polyhedral Oligomeric Silsesquioxane (POSS) Cage on the Epoxy-POSS Hybrid Materials Properties

This paper reports the synthesis of new reinforcing agents based on sodium montmorillonite modified with some polyhedral oligomeric silsesquioxanes. The modified montmorillonite was extensively characterized using different techniques such as Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction and X-ray photoemission spectroscopy. The obtained reinforcing agents were used for the synthesis of epoxy-based nanocomposites. The nanocomposites were studied using thermal analysis, dynamic mechanical analysis, differential scanning calorimetry and thermogravimetric analysis to conclude that the type of radicals on the POSS cage may influence the properties of the final nanocomposites.

Novel water and oil repellent POSS-based organic/inorganic nanomaterial: Preparation, characterization and application to cotton fabrics

A series of polyhedral oligomeric silsesquioxane (POSS) based hybrid terpolymers P(POSS-MMA-(HFPO)3MA) were synthesized and characterized by NMR, FT-IR, GPC, DSC and TG. The thermal properties of these terpolymers were improved by the introduction of POSS cage. The cotton fabrics coated with these terpolymers possessed excellent water and oil repellency. The water and salad oil contact angle could be achieved from ∼140° to 152° and from ∼127° to 144° respectively as the content of POSS in the terpolymer increased from 6.4 wt% to 13.4 wt%. Compared with P(MMA-(HFPO)3MA) copolymer-coated cotton fabrics, POSS-based terpolymer coated cotton fabrics showed better oil repellency with a tendency of first increasing and then decreasing with an increase of the POSS content. The n-hexadecane (surface tension: 27.4 mN/m, 20 °C) contact angle reached ∼117° for coated cotton fabrics with terpolymer containing 9.5 wt% of POSS.

Thermal Transitions and Reaction Kinetics of Polyhederal Silsesquioxane containing Phenylethynylphthalimides

Thermal transitions and reaction kinetics of polyhedral oligomeric silsesquioxane (POSS) with phenylethynylphthalimide (PEPI) moieties were investigated. Specifically, this study was designed to probe the influence of the POSS peripheries, types of spacer group in between the PEPI and the SiO1.5 core, the architecture of the PEPI arrangement with respect to the SiO1.5 core, and the number of PEPI groups per cage on the thermal transitions and the cross-linking reaction of phenylethynyl. PEPI−POSS compounds with isobutyl peripheries exhibited lower melting temperatures as compared to those with phenyl periphery, consequently these isobutyl PEPI−POSS derivatives have a higher phenylethynyl reaction rate, although the onset of reaction temperature was not significantly affected. Changing the spacer group from propyl to phenyl causes an increase in the melting transition temperature along with a higher heat of fusion at melting; however, the more rigid phenyl spacer enables the PEPI−POSS to form a higher degree of crystallinity upon cooling. The more rigid phenyl spacer also initiates the polyene reactions at lower temperatures. For POSS with PEPI attached to either side of the cage, there are two isomers with respect to the SiO1.5 core. This mixture of two isomers inhibits the formation of crystallinity as compared with the “pendent” derivative where both PEPI groups come off from the same corner of POSS cage. Finally, it was found that these PEPI−POSS molecules have reaction kinetics and onset temperatures on par with organic hexafluorophenylethynyl oligoimides, which make these PEPI−POSS molecules excellent candidates as nanocomposite additives in high performance composite applications.

Preparation, Characterization, and Properties of Novel Polyhedral Oligomeric Silsesquioxane−Polybenzimidazole Nanocomposites by Friedel−Crafts Reaction

The organic−inorganic nanocomposites involving OPBI (poly[2,2′-(p-oxidiphenylene)-5,5′-bibenzimidazole]) and polyhedral oligomeric silsesquioxane (POSS) were prepared via in situ polymerization of 4,4′-dicarboxydiphenyl ether (DCDPE) and 3,3′-diaminobenzidine (DABz) in the presence of the POSS where the organic group on silsesquioxane cage is phenyl. NMR, XPS, and XRD characterization of POSS-g-OPBI, purified from the POSS-g-OPBI/OPBI hybrid, revealed that the OPBI chains were successfully attached to the phenyl group of the POSS through Friedel−Crafts (F−C) reaction. The homogeneous dispersion of POSS cages in the polymer matrix was evidenced by SEM. The DMA results showed that the moduli of the POSS-g-OPBI/OPBI nanocomposites were significantly higher than OPBI matrix, indicating the nano-reinforcement effect of POSS cages. Thermogravimetric analysis indicated that the thermal stability of the polymer matrix was not sacrificed but improved by introducing a small amount of POSS since POSS showed lower thermal stability than OPBI. More importantly, the mechanical properties, including tensile and yield strength, Young’s modulus, and toughness, were obviously simultaneously increased by introducing POSS into the nanocomposite, which is quite differently from the traditional nanocomposites, where the ductility and toughness of polymer were usually reduced substantially upon the incorporation of inorganic reinforced agent.

Octasilsesquioxane-reinforced DGEBA and TGDDM epoxy nanocomposites: Characterization of thermal, dielectric and morphological properties

Epoxy resin nanocomposites, based on the diglycidyl ether of bisphenol-A (DGEBA) and tetraglycidyl diamino diphenyl methane (TGDDM), are prepared via in situ co-polymerization with 4,4′-diaminodiphenylsulfone (DDS) in the presence of octa-aminophenyl silsesquioxane (OAPS) at levels of up to 20 wt.% of the latter. The curing reaction involving epoxy, DDS and OAPS is investigated using Fourier transform infrared (FTIR) spectroscopy. Differential scanning calorimetry and dynamic mechanical analysis show that the glass transition temperatures of the polyhedral oligomeric silsesquioxane (POSS) containing nanocomposites are higher than the corresponding neat epoxy systems at lower concentrations of POSS (⩽3 wt.%). Thermogravimetric analysis indicates that the POSS–epoxy nanocomposites display high ceramic yields, suggesting improved flame retardancy. The increasing concentration of OAPS into epoxy–amine networks exhibits a decreasing trend in the values of dielectric constant compared with those values obtained from neat epoxy systems. The higher epoxy functionality present in TGDDM leads to nanocomposites which possess enhanced thermal stability and higher dielectric constants than the DGEBA-based nanocomposites. X-ray diffraction analysis reveals that the molecular level reinforcement of POSS cages occurs in both the cases of DGEBA- and TGDDM-based hybrid epoxy nanocomposites. Furthermore, homogeneous dispersion of POSS cages in the epoxy matrices is evidenced by scanning electron microscopy, which further confirms that the POSS molecule has become an integral part of the organic–inorganic inter-cross-linked network systems.

Dye‐Doped Polyhedral Oligomeric Silsesquioxane (POSS)‐Modified Polymeric Matrices for Highly Efficient and Photostable Solid‐State Lasers

AbstractHere, the design, synthesis, and characterization of laser nanomaterials based on dye‐doped methyl methacrylate (MMA) crosslinked with octa(propyl‐methacrylate) polyhedral oligomeric silsesquioxane (8MMAPOSS) is reported in relation to their composition and structure. The influence of the silicon content on the laser action of the dye pyrromethene 567 (PM567) is analyzed in a systematic way by increasing the weight proportion of POSS from 1 to 50%. The influence of the inorganic network structure is studied by replacing the 8MMAPOSS comonomer by both the monofunctionalized heptaisobutyl‐methacryl‐POSS (1MMAPOSS), which defines the nanostructured linear network with the POSS cages appearing as pendant groups of the polymeric chains, and also by a new 8‐hydrogenated POSS incorporated as additive to the polymeric matrices. The new materials exhibit enhanced thermal, optical, and mechanical properties with respect to the pure organic polymers. The organization of the molecular units in these nanomaterials is studied through a structural analysis by solid‐state NMR. The domain size of the dispersed phase assures a homogeneous distribution of POSS into the polymer, thus, a continuous phase corresponding to the organic matrix incorporates these nanometer‐sized POSS crosslinkers at a molecular level, in agreement with the transparency of the samples. The silicon–oxygen core framework has to be covalently bonded into the polymer backbone instead of being a simple additive and both the silica content and crosslinked degree exhibit a critical influence on the laser action.

The effect of incorporation of POSS units on polymer blend compatibility

AbstractIn this work, the compatibility of poly(methyl methacrylate) (PMMA) and polystyrene (PS) polymers with their polyhedral oligomeric silsesquioxane (POSS) copolymers combined by solution blending is investigated, to determine the effect of incorporation of the POSS unit on polymer compatibility. The morphology of these tethered POSS copolymer/polymer blends was studied by electron microscopy, thermal analysis, and density. Although the basic PS/PMMA blend was clearly immiscible, it was also found that the incorporation of POSS into the PS chain led to incompatibility when the POSScoPS copolymer was blended with PS homopolymer. However, conversely, in the case where the POSS moiety was included as part of a copolymer with PMMA, the copolymer was miscible with the PMMA homopolymer. The presence of isobutyl units on the corners of POSS cage is clearly sufficient to encourage miscibility with PMMA. Interestingly, blends of the two different POSS copolymers led to an immiscible structure, despite having the common POSS units, the interactions between the POSS moieties clearly not being sufficient to drive compatibility. The POSS copolymers have also been used as interfacial agents in immiscible PS and PMMA blend, and it has been found that the appearance of the interface bonding is improved, although the phase morphology is only slightly changed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010