Epoxy Polyhedral Oligomeric Silsesquioxane Research Articles

Planetary cross-linked structure design of hybrid organosilica membrane by amine-driven polymerization for CO2 separation

A hybrid organosilica membrane, with a unique 3-dimensional planetary crosslinked network was fabricated for investigating the effect of in-situ crosslinked network synthesis on the membrane structure. Herein, a dual reaction approach was introduced for the copolymerization. 3-Aminopropyltriethoxysilane (APTES) consisting of amide acts as a shell covering the core cage polyhedral oligomeric silsesquioxane (POSS). Epoxy POSS was selected to construct a tough and 3D free volume as the host for organosilica, to promote gas transport and facilitate a mild reaction with the amide functional group, through the ring-open polymerization without a catalyst. As a branched-chain modified unit, APTES can increase the crosslink density to form the final structure such as a planetary orbit. As a result, it was confirmed that the as-prepared M-0.1A1P(a) formed a planetary structure, from the Si–C main structure surrounded by N using FE-TEM. Moreover, M-0.1A1P(a) showed a maximum selectivity of 77.71 towards CO2/N2, 93.79 towards CO2/CH4, 121.32 towards H2/N2, and 144.86 towards H2/CH4, and an adequate hydrogen permeance of 1.41 × 10−8 mol/(m2sPa) at around 25 °C, confirming that this type of cross-linked network has full potential for the application of small molecular gas separation, especially for CO2.

UV Curable Robust Durable Hydrophobic Coating Based on Epoxy Polyhedral Oligomeric Silsesquioxanes (EP-POSS) and Their Derivatives.

Hydrophobic coatings have considerable potential applications in many fields. Ease of operation and high durability are essential for practical use. Fast curing and being solvent-free are a plus, and if they possess certain characteristics (antigraffiti, good adhesion, high hardness, heat resistance, wide range of applicability, etc.) at the same time, it is a dream solution. Herein, a facile one-step approach with the above features was reported for a UV curable robust hydrophobic coating based on Epoxy Polyhedral Oligomeric Silsesquioxanes (EP-POSSs). The structure and surface morphology of these EP-POSSs and their derivatives were systematically studied. Because of the core-in-cage structure which was constructed by repeating units of R-Si(O1/2)3 and the strong covalent bonds of Si–C and Si–O, the coatings displayed high pencil hardness (6–8H), high thermal stability with initial decomposition temperature around 350–400 °C, and a high water contact angle (up to 108.06°) even after outdoor exposure for a month. These POSSs and their derivatives are expected to find uses in various applications such as stain resistance, self-cleaning, scratch resistance, and cigarette moxibustion resistance of wood furniture, kitchenware, and medical and industrial appliances.

Properties of Epoxy-POSS Composites at Low Temperature Based on Molecular Dynamics Simulation

The epoxy resin is an important part of superconducting devices, and nanoparticles can improve the properties of the epoxy resin at low temperature. However, the performance of epoxy/nanoparticles composites at low temperature is still unclear. In this work, pure epoxy and three epoxy-polyhedral oligomeric silsesquioxanes (POSS) composites models are proposed. The results of molecular dynamics (MD) simulation show that POSS nanoparticles can improve the mechanical properties (bulk modulus, Young's modulus and shear modulus) of the epoxy at low temperature. As for the mean square radius of gyration and the mean square displacement, different organic groups in POSS particles have different effects on the epoxy resin.

Recyclable and reprocessable epoxy-polyhedral oligomeric silsesquioxane (POSS)/mesogenic azobenzene/poly (ethylene-co-vinyl acetate) composites with thermal- and light-responsive programmable shape-memory performance

In this study, an Epoxy/POSS-liquid crystalline azobenzene-Poly (ethylene-co-vinyl acetate) (Epoxy/POSS-Azo-EVA) composite was prepared via the thermal curing of epoxy monomers and multi-functional thiol-containing Polyhedral oligomeric silsesquioxane (POSS) in an EVA matrix. The EVA matrix afforded the composite with shape memory performance. Epoxy/POSS polymer was uniformly dispersed in the matrix to act as a rigid skeleton, leading to the improvement of the mechanical properties and shape memory performance of the composite. Liquid crystalline azobenzene as the photosensitive component provided the inner stress to render the composite film with photo-induced shape-deformation behavior under UV light. The composite film not only exhibited thermal- and light-responsive programmable shape-memory behavior stimulated by heat and light, but also was recyclable and reprocessable. Moreover, the recycled composite film was processed into different functional devices. A flexible photomechanical device based on the recycled Epoxy/POSS-Azo-EVA composite film was fabricated, and the soft device deformed into a hook-shape under UV light and hooked an object whose weight is larger than that of the device. A smart wire was also prepared via assembling a stretched recycled Epoxy/POSS-Azo-EVA composite film and a copper foil by adhesive. The wire could control the status of a circuit via changing its shape under UV light and maintain the status after the removal of light. The functional devices described in this work only needed a short time of UV irradiation during a work cycle, and the devices still held the temporary shape in the absence of UV irradiation. The recyclable and reprocessable Epoxy/POSS-Azo-EVA composite film in this work could provide a creative approach for the fabrication of novel photomechanical devices and soft robotics with energy-saving, intelligence, recyclability, and sustainability.

Polyhedral oligomeric silsesquioxane (POSS)-based epoxy nanocomposite involving a reversible Diels–Alder-type network as a self-healing material

Epoxy-polyhedral oligomeric silsesquioxane (POSS) nanocomposites were prepared by incorporating POSS nanofiller into the epoxy-amine network. The monofunctional epoxy-POSS monomer or nonfunctional octaphenyl POSS unit were applied to reinforce the epoxy network by producing the nanocomposite with chemically bound pendant POSS or physically admixed POSS. The combination of reactive and unreactive POSS, leads to a synergistic effect and to the most efficient reinforcement of the epoxy network. Both polymer-POSS and POSS–POSS interactions are present in the system and lead to a strong physical crosslinking through the path polymer-bound POSS-unbound POSS domain. The nanocomposite was modified by incorporation of the thermoreversible Diels–Alder (DA) type network. The produced interpenetrating network composed of the irreversible reinforced epoxy and the reversible DA networks exhibits an efficient self-healing capability. This strong nanocomposite, showing a modulus of 800 MPa at room temperature, was healed with an efficiency of 61%. The developed stiff nanocomposite is shown to be a promising material because self-healing of strong thermosets is still a big challenge. With the increasing content of POSS nanofiller and heterogeneity of the nanocomposite, however, the healing efficiency diminishes. The insufficient contact of crack surfaces due to involved inhomogeneities results in a worse sealing of the material crack.

Fabrication of a mechanically tough and strong SiO2@EPOSS modified novolac phenolic network by simultaneously improving its crosslinking inhomogeneity and crosslinking density

Simultaneously improving mechanical strength and toughness of thermosetting polymer nanocomposites remains a great challenge even though massive efforts have been made by controlling the aggregation and interface interaction of nanoparticles. In fact, crosslinking inhomogeneity and crosslinking density of thermosetting polymer nanocomposites can also profoundly affect the competing mechanical properties. Due to their conflicting influence on the toughness and strength of thermosetting polymer nanocomposites, the difficulty lies in how to coordinate the influence effectively. In this work, a mechanically tough and strong novolac phenolic nanocomposites (ESNH) were successfully constructed by introducing a reactive core-shell POSS with nanosilica as core and epoxy-polyhedral oligomeric silsesquioxane as shell (SiO2@EPOSS) (ES). Via controlling the quantity and the size of self-polymerized ES phase domain, the crosslinking inhomogeneity and crosslinking density of ESNH can be diversely tuned. Especially for 3%ESNH-3%, remarkably enhanced tensile properties and fracture toughness were realized. The self-polymerized ES phase domain with relatively small quantity and size was homogeneously grafted in phenolic networks, which could pin microstructural interfaces and junct nodular domains of phenolic networks, synergistically improving the crosslinking inhomogeneity and crosslinking density. Therefore, the moderately self-polymerized ES phase domain in the phenolic networks was remarkably contributed to coordinating the performance between the fracture toughness and tensile property. This study provides a novel and efficient envision toward simultaneously improving the toughness and strength of thermosetting polymer nanocomposites via tuning their curing behavior and the corresponding microstructure.

Epoxy-polyhedral oligomeric silsesquioxanes (POSS) nanocomposite vitrimers with high strength, toughness, and efficient relaxation

Although considerable progress has been made in developing vitrimers, on-going challenges for vitrimers for high-performance applications include the improvement in mechanical properties and identification of more efficient exchange reactions. By incorporation of glycidyl polyhedral oligomeric silsesquioxane (POSS) as a nanoscale filler in epoxy, we produced epoxy-POSS nanocomposite vitrimers that show high strength, toughness, thermal stability, and efficient relaxation. With 10 wt% POSS, the ultimate tensile strength and strain at break of the epoxy-POSS nanocomposite vitrimers increased by ~64% and ~76%, respectively, while at 160 °C the stress relaxation time increased by ~260% in comparison to that of pure epoxy vitrimer. The epoxy-POSS nanocomposite vitrimers show high malleability due to the efficient transesterification reaction and re-processability with little degradation of their initial mechanical properties, suggesting opportunities for sustainable plastics.

A low-shrinkage dental composite with epoxy-polyhedral oligomeric silsesquioxane

Polymerization shrinkage and mechanical properties affect the service life of dental restorative composites. Polyhedral oligomeric silsesquioxanes (POSS) can be an efficient strategy to improve the shrinkage properties and mechanical properties simultaneously. In this work, epoxycyclohexyl POSS (E-POSS) was used to modify the Bis-GMA/TEGDMA dental resins. E-POSS were introduced into the acrylic resin system via ring-opening reaction, and a cationic/free radical hybrid system was obtained. Double bond conversion, glass transition temperature, heterogeneity, crosslink density of dental resins and volumetric shrinkage, water sorption/solubility, flexural strength/modulus of dental composites were investigated. As the introduction of E-POSS caused higher double bond conversion and lower crosslink density, the polymerization shrinkage was significantly reduced to 2.91% (p < 0.05) and the flexural strength increased to 117.19 MPa (p < 0.05) compared to the control sample (5.06%, 99.16 MPa, p<0.05). Lower water sorption and solubility were also observed in composites contained E-POSS (p < 0.05).

Curing behavior and microstructure of epoxy-POSS modified novolac phenolic resin with different substitution degree

Easily oxidized group and rigid structure of phenolic resin (PR) network can result in brittleness and low char yield at high temperatures, which limits the widespread applications of PR in harsh environment. Whilst organic-inorganic hybrid material, such as POSS-containing material was introduced to enhance PR, the microstructure and the thermo-mechanical properties of the hybrid material modified PR are not well understood. Therefore, in the work, a novel organic-inorganic hybrid networks (ENH) were prepared with epoxy-polyhedral oligomeric silsesquioxane (EPOSS) modified novolac phenolic resin (EN) and hexamethylenetetramine (HMTA) to further clarify the curing behavior and its relation to microstructure and the resulting thermal-mechanical properties. Here, the curing characteristics of ENH were discussed by usinag advanced isoconversional method and Fourier transform infrared spectroscopy (FTIR). It was revealed that a diversity of crosslinking networks was exhibited after curing ENH, including EPOSS-NR crosslinked, tethered structure, and self-polymerized structure of EPOSS as well as NH networks. When the substitution degree of EPOSS is relatively low, EPOSS serves as a junction point to further improve the crosslinking density of ENH networks, leading to better thermo-mechanical properties, thermal stability and tensile property as well as lower dielectric properties. However, as the self-polymerization of EPOSS increased, the NH network was dramatically disrupted and the thermo-mechanical properties, thermal stability and tensile property of ENH were deteriorated.

Preparation and characterization of nanocomposite films by hybrid cationic ring opening polymerization of glycidyl-POSS

Epoxy-polyhedral oligomeric silsesquioxanes (G-POSS) monomers were synthesized from 3-glycidyloxypropyl-trimethoxysilane (GTMS) by hydrolytic condensation. The G-POSS-containing nanocomposite film was prepared by hybrid cationic ring-opening polymerization from G-POSS and GTMS. The curing reaction kinetics, dynamical mechanical properties, thermal degradation properties and morphological structures of G-POSS/GTMS system were investigated by non-isothermal DSC, dynamic mechanical analysis (DMA), TGA, AFM and SEM. The results show that the curing reaction activation energy Ea decrease when GTMS is added into the reaction system, and the curing reaction kinetics can be simulated by the Šesták–Berggren (S–B) model. DMA and TG analysis results show that the glass transition temperature Tg and initial thermal decomposition temperature Tid of materials is 4 and 65 °C higher than pure polymerized G-POSS, respectively, when the content of GTMS is 2 wt%. AFM analysis shows that the membrane surface of pure polymerized G-POSS has uniform distribution of less than 1.76 nm high protrusion. SEM analysis shows that have uniform spherical particle distribution on the membrane surface with about 20–25 nm diameter.

Structure ordering and reinforcement in POSS containing hybrids

The rubbery Epoxy–POSS (polyhedral oligomeric silsesquioxane) hybrid networks have been prepared by incorporating the novel diepoxy–POSS monomer in an epoxy network. During the hybrid network formation, monitored in situ by SAXS, the POSS units self-assemble to form crystalline lamellae in the epoxy matrix. The ordered organic–inorganic hybrid shows the temperature induced order–order and order–disorder transitions due to breaking the POSS domains. The proposed structural model of the hybrid involves the ordered POSS lamellae and cylinders as well as the disordered arrangement of POSS units. Dynamics of the self-assembly processes was investigated by DMA measured at different frequencies of shear deformation. The well-arranged POSS domains provide the hybrid with a significant reinforcement. Moreover, the hybrid with a high POSS content undergoes a strain induced stiffening due to rearrangement of the ordered structure. The effect of POSS–POSS interactions on the hybrid ordering and reinforcement is discussed.

Thermal, mechanical and dielectric properties of nanostructured epoxy-polyhedral oligomeric silsesquioxane composites

This paper presents the results of the thermal, mechanical and dielectric measurements conducted on polymer nanocomposites consisting of epoxy and polyhedral oligomeric silsesquioxane (POSS). The material composites were analyzed with a scanning electron microscope (SEM), an atomic force microscope (AFM) and a transmission electron microscope (TEM). Glass transition temperatures of the composites were measured with differential scanning calorimeter (DSC). Stress, strain, modulus and impact strength of epoxy nanocomposites were tested. Ac and lightning impulse (LI) breakdown strength of the composites were measured. Relative permittivity, loss factor and volume resistivity measurements were also conducted on the material samples. Two types of POSS, glycidyl and octaglycidyldimethylsilyl, were used in different quantities. Statistical analysis was applied to the measurement results to determine the effects of the additive type and amount on the properties of epoxy. The paper discusses the possibilities and restrictions in order to achieve advantages in high voltage applications using polyhedral oligomeric silsesquioxanes.

Synthesis and Characterization of a POSS-Maleimide Precursor for Hybrid Nanocomposites

Epoxy polyhedral oligomeric silsesquioxane (POSS)-based hybrid nanocomposites were prepared by in situ polymerization of a homogeneous blend of the diglycidylether of bisphenol-A and 4,4'diaminodiphenylmethane (DDM) in the presence of octa(maleimidophenyl)silsesquioxane. The reaction of a maleimido-functionalized POSS cube with the epoxy resin was studied by Fourier transform infrared analysis and the formation of nanocomposites was confirmed by wide-angle X-ray diffraction and scanning electron microscopy. Dynamic mechanical analysis studies indicated that the crosslinking structures of the nanocomposite networks were predominantly formed between the terminal maleimide double bonds and the amino groups of DDM through a Michael addition reaction to form an aspartimide. The values of the glass transition temperatures ( Tg) decreased with increasing POSS-maleimide content and this was likely to be due to the inclusion of POSS cages into the system and the consequent increase in free volume. The dynamic thermal stability of the cured polymers was increased by increasing the POSS content in the hybrid epoxy matrices as evidenced from thermogravimetric analysis data.

Polyimide and polyhedral oligomeric silsesquioxane nanocomposites for low-dielectric applications

A novel polyimide (PI) hybrid nanocomposite containing polyhedral oligomeric silsesquioxane (POSS) with well defined architecture has been prepared by copolymerization of octakis(glycidyldimethylsiloxy)octasilsesquioxane (Epoxy–POSS), 4,4′-oxydianiline diamine (ODA), and 4,4′-carbonyldiphthalic anhydride (BTDA). In these nanocomposite materials, the equivalent ratio of the Epoxy–POSS and ODA are adjustable, and the resultant PI–POSS nanocomposites give variable thermal and mechanical properties. More importantly, we intend to explore the possibility of incorporating POSS moiety through the Epoxy–POSS into the polyimide network to achieve the polyimide hybrid with lower dielectric constant (low- k) and thermal expansion. The lowest dielectric constant achieved of the POSS/PI material (PI-10P) is 2.65 by incorporating 10 wt% Epoxy–POSS (pure PI, k=3.22). In addition, when contents of the POSS in the hybrids are 0, 3, 10 wt% (PI-0P, PI-3P, PI-10P), and the resultant thermal expansion coefficients (TEC) are 66.23, 63.28, and 58.25 ppm/°C, respectively. The reduction in the dielectric constants and the resultant thermal expansion coefficients of the PI–POSS hybrids can be explained in terms of creating silsesquioxane cores of the POSS and the free volume increase by the presence of the POSS–tethers network resulting in a loose PI structure.

Structure Within Thin PolymerNanocomposite Films

The structure of single layer epoxy-polyhedral oligomeric silsesquioxanes (POSS) nanocomposite films and the effects of the POSS nanoparticle addition on the swelling of a single layer of epoxy films on silicon substrates is investigated by neutron reflectivity (NR) as a function of the resin/crosslinker composition and cure temperature. The microstructure of the nanocomposite films is examined by swelling the films with the good solvent d-nitrobenzene (dNB). The main result is a large suppression of swelling in the surface and nearsurface regions and the bulk of the film. This may be due to the blocking of the solvent molecules that intend to diffuse into the network of epoxy film. It is known that the resin/curing agent composition dependence of the swelling in single layer epoxy films is likely to be due to the preferential segregation of the curing agent. In contrast we observe that the suppression of swelling of the epoxy-POSS nanocomposite films is only slightly dependent on the resin/curing agent composition, which is probably due to the preferential segregation of the POSS nanoparticles to the surface or near-surface region. Additionally, we demonstrate that the cross-link density normal to the substrate surface is uniform for the epoxy films with 3% POSS whereas variation in the crosslink density is observed for the epoxy films without the POSS nanoparticles.