Thermal and dynamic mechanical properties of epoxy resin/poly(urethane‐imide)/polyhedral oligomeric silsesquioxane nanocomposites

Linear isocyanate‐terminated poly(urethane‐imide) (PUI) with combination of the advantages of polyurethane and polyimide was directly synthesized by the reaction between polyurethane prepolymer and pyromellitic dianhydride (PMDA). Then octaaminophenyl polyhedral oligomeric silsesquioxane (OapPOSS) and PUI were incorporated into the epoxy resin (EP) to prepare a series of EP/PUI/POSS organic–inorganic nanocomposites for the purpose of simultaneously improving the heat resistance and toughness of the epoxy resin. Their thermal degradation behavior, dynamic mechanical properties, and morphology were studied with thermal gravimetric analysis (TGA), dynamic mechanical analysis (DMA), and transmission electron microscope (TEM). The results showed that the thermal stability and mechanical modulus was greatly improved with the addition of PUI and POSS. Moreover, the EP/PUI/POSS nanocomposites had lower glass transition temperatures. The TEM results revealed that POSS molecules could self assemble into strip domain which could switch to uniform dispersion with increasing the content of POSS. All the results could be ascribed to synergistic effect of PUI and POSS on the epoxy resin matrix. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermo-oxygen degradation mechanisms of POSS/epoxy nanocomposites

A series of polyhedral oligomeric silsesquioxane/epoxy nanocomposites (POSS/EP) containing 0 wt%, 5 wt%, 10 wt% and 15 wt% content of POSS were prepared. Mechanical properties were used as the index to show the effect of POSS on the thermo-oxygen degradation resistance of epoxy resin. And the thermo-oxygen degradation mechanism was investigated by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Results showed that the incorporation of POSS into epoxy networks enhanced the thermo-oxygen resistance of epoxy. POSS led to the formation of inert layer on the surface of materials which could protect the internal structure from decomposition. As a result, the retention of mechanical properties of EP/POSS hybrids increased with the POSS content increasing.     

Synthesis of raspberry-like monodisperse magnetic hollow hybrid nanospheres by coating polystyrene template with Fe(3)O(4)@SiO(2) particles

A new inorganic/organic hybrid material containing silsesquioxane was prepared by the reaction of caged octa (aminopropyl silsesquioxane) (POSS-NH(2)) with n-butyl glycidyl ether (nBGE) and 1,4-butanediol diglycidyl ether (BDGE). The copolymers of POSS, nBGE, and BDGE could be obtained with varied feed ratio of POSS-NH(2), nBGE, and BDGE in the preparation. The hybrid material was added into an epoxy resin (E51) for enhancing the toughening and thermal properties of the epoxy resin. The results showed that the toughening and the thermal properties of the cured epoxy resin were greatly improved by the addition of the hybrid. The enhancement was ascribed to nano-scale effect of the POSS structure and the formation of anchor structure in the cured network. The investigation of kinetics for the curing process of the hybrid-modified epoxy resin revealed that two kinds of curing reactions occurred in different temperature ranges. They were attributed to the reactions between amino groups of the curing agent with epoxy groups of E51 and with residue epoxy groups in the hybrid. The reacting activation energies were calculated based on Kissinger's and Flynn-Wall-Ozawa's methods, respectively.     

Thermal degradation behaviors of epoxy resin/POSS hybrids and phosphorus–silicon synergism of flame retardancy

Epoxy resin (EP)/polyhedral oligomeric silsesquioxane (POSS) hybrids were prepared based on octavinyl polyhedral oligomeric silsesquioxane (OVPOSS) and phosphorus‐containing epoxy resin (PCEP). The PCEP was synthesized via the reaction between bisphenol A epoxy resin (DGEBA) and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO). The structure and morphology of PCEP/OVPOSS hybrids were characterized by Fourier transform infrared spectroscopy and transmission electron microscopy. Differential scanning calorimetry revealed that the PCEP/OVPOSS hybrids possessed higher glass transition temperatures than that of PCEP. The thermal stability of the PCEP/OVPOSS hybrids was studied using thermogravimetric analysis (TGA). The TGA results illustrated the synergistic effect of phosphorus–silicon of flame retardancy: phosphorus promotes the char formation, and silicon protects the char from thermal degradation. The thermal degradation mechanism of the PCEP/OVPOSS hybrids was investigated by real time Fourier transform infrared spectra and pyrolysis/gas chromatogram/mass spectrometry (Py‐GC/MS) analysis. It was found that OVPOSS migrated to the surface of the matrix and then sublimed from the surface in nitrogen; whereas, the vinyl groups of OVPOSS were oxidated to form a radical trap which could react with pyrolysis radicals derived from PCEP to form the branched and crosslinked structure in air. The combustion behaviors of the hybrids were evaluated by micro combustion calorimetry. The addition of OVPOSS obviously decreased the value of peak heat release rate and total heat release of the hybrids. Moreover, scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy were used to explore the char residues of the PCEP and the hybrids. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 693–705, 2010     

Flame retardant epoxy composites with epoxy‐containing polyhedral oligomeric silsesquioxanes

A kind of polyhedral oligomeric silsesquioxanes (POSS) containing the propoxyl‐epoxy and phenyl groups (pr‐ep‐Ph‐POSS) was synthesized via hydrolytic condensation reaction. Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry identified the structure of the pr‐ep‐Ph‐POSS, including major caged Si₆O₉ (T6), Si₁₀O₁₅ (T10), Si₁₂O₁₈ (T12), etc. The pr‐ep‐Ph‐POSS was applied into the epoxy resin to achieve EP/pr‐ep‐Ph‐POSS composites. Thermogravimetric analysis indicated that EP/pr‐ep‐Ph‐POSS showed excellent thermal properties than pure EP. The fire behaviors of EP/pr‐ep‐Ph‐POSS composites were evaluated based on the cone calorimetry, limiting oxygen index (LOI), UL‐94 vertical burning test, and smoke density test. The smoke density decreased by ~30%, the LOI value reached to 26.4%, dripping was inhibited, and the peak of heat release rate decreased by ~62%. X‐ray photoelectron spectroscopy analysis and FTIR indicated that protective‐barrier effect is the main flame‐retardant mode of action for pr‐ep‐Ph‐POSS, due to the formation of the Si‐O‐Si, Si‐O‐C, and Si‐C condensed phase, which improve the thermal stability, strength, and integrity of the char layer.     

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

Fiber-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     

Synthesis and thermal characterization of phosphorus containing siliconized epoxy resins

Siliconized epoxy matrix resin was developed by reacting diglycidyl ethers of bisphenol A (DGEBA) type epoxy resin with hydroxyl terminated polydimethylsiloxane (silicone) modifier, using γ-aminopropyltriethoxysilane crosslinker and dibutyltindilaurate catalyst. The siliconized epoxy resin was cured with 4, 4-diaminodiphenylmethane (DDM), 1,6-hexanediamine (HDA), and bis (4-aminophenyl) phenylphosphate (BAPP). The BAPP cured epoxy and siliconized epoxy resins exhibit better flame-retardant behaviour than DDM and HDA cured resins. The thermal stability and flame-retardant property of the cured epoxy resins were studied by thermal gravimetric analysis (TGA) and limiting oxygen index (LOI). The glass transition temperatures (T_g) were measured by differential scanning calorimetry (DSC) and the surface morphology was studied by scanning electron microscopy (SEM). The heat deflection temperature (HDT) and moisture absorption studies were carried out as per standard testing procedure. The thermal stability and flame-retardant properties of the cured epoxy resins were improved by the incorporation of both silicone and phosphorus moieties. The synergistic effect of silicone and phosphorus enhanced the limiting oxygen index values, which was observed for siliconized epoxy resins cured with phosphorus containing diamine compound.     

Effects of TriSilanolIsobutyl-POSS on thermal stability of methylsilicone resin

Methylsilicone resin/polyhedral oligomeric silsesquioxane (POSS) composites with various proportions of POSS monomer were synthesized by the reaction of functionalized TriSilanolIsobutyl-POSS macromonomer with hydroxyl-terminated methylsilicone resin. The structures of the obtained hybrid polymers were characterized with Fourier-transformed infrared (FT-IR) and transmission electron microscopy (TEM). The FT-IR spectra suggested successful bonding of TriSilanolIsobutyl-POSS and methylsilicone resin. TEM analysis showed that POSS can dissolve in methylsilicone resin at the molecular level. The influences of TriSilanolIsobutyl-POSS on the thermal stability and degradation behavior of methylsilicone resin were studied by thermogravimetric analysis (TGA), solid-state ²⁹Si NMR and X-ray photoelectron spectroscopy (XPS). All these techniques showed that TriSilanolIsobutyl-POSS incorporation results in increased decomposition temperatures and oxidation resistance, primarily by reducing the effect of silanol end groups on the thermolysis through condensation reaction of Si-OH groups and partial loss of isobutyl followed by the formation of an inorganic SiO₂ layer to prevent methylsilicone from further degradation.     

含磷有机硅杂化环氧树脂固化体系性能研究

通过磷酸与γ-环氧丙氧基三甲氧基硅烷反应得到含磷有机硅氧烷,并加入到环氧树脂/4,4'-二氨基二苯基甲烷体系中混合,通过溶胶-凝胶的方法制备了含磷有机硅杂化环氧树脂固化物.对固化体系进行了玻璃化转变温度、热失重、阻燃、拉伸强度、冲击强度测试分析.结果表明,该固化体系的阻燃性得到提高,极限氧指数在25.8～29.3,玻璃化转变温度得到提高,在161～179℃;虽然初始分解温度比纯环氧树脂固化物低,但800℃残炭率可以达到26.5%,提高了36%;拉伸强度得到提高,在71～94 MPa,冲击强度可以达到14.36 kJ/m2,提高了14%.该固化体系具有较好的阻燃性能和热性能,同时具有较好的力学性能.     

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.     

树状硅基大分子光引发剂的合成与表征

从Vogtle等[1]首次描述了“串级式”合成方法以来,以及Newkome[2]和Tomalia等[3]的重要贡献,具有完美的支化结构、高度对称且分子大小可精确控制的树状分子在当代化学领域中已经成为一个重要的研究方向,其新颖的结构,独特的性能吸引了众多科学工作者的兴趣[4,5].其中硅基树状分子,尤其是树状聚硅碳烷大分子由于具有可变的支化度、无论是动力学还是热力学上的高度稳定性的优点,以及Si—Cl、Si—H、Si—OH等基团的的存在使得易于根据不同的需要对树状大分子进一步功能化改性,已成为高分子领域的研究热点[6,7],例如树状硅碳烷液晶[8~10]、…     

Improving Damping Properties and Thermal Stability of Epoxy/Polyurethane Grafted Copolymer by Adding Glycidyl POSS

Modified castor oil-based epoxy resin (EP)/polyurethane (PU) grafted copolymer by glycidyl polyhedral oligomeric silsesquioxane (glycidyl POSS) was synthesized. The damping properties, thermal stability, mechanical properties and morphology of the grafted copolymer modified by glycidyl POSS were studied systematically. The results revealed that the incorporation of glycidyl POSS improved the damping performance evidently and broadened damping temperature range, especially when the glycidyl POSS content was0.2%–1%. At the same time, there was a slight increase in thermal stability with the increase of POSS content. The tensile properties changed with the change of the copolymer's Tg, decreased at low POSS contents and increased at high POSS contents. This modified copolymer has the potential to be used as film damping material or constrained damping layer.     

Thermal behaviour and mechanical properties of novel RTV silicone rubbers using divinyl-hexa[(trimethoxysilyl)ethyl]-POSS as cross-linker

Divinyl-hexa[(trimethoxysilyl)ethyl]-POSS (DVPS) as an octavinyl-POSS derivative was first prepared. A series of novel polydimethylsiloxane (PDMS)/DVPS hybrid materials as room temperature vulcanized (RTV) silicone rubber were prepared. The chemical incorporation of novel POSS into hydroxyl-terminated PDMS system by hydrolytic condensation reaction was verified by attenuated total reflection (ATR) infrared spectroscopy. Thermal degradation, thermo-oxidative stability and mechanical properties of these novel RTV silicone rubbers were studied by means of thermogravimetric analysis and tensile testing. The results exhibited significantly enhanced effects on the thermal stabilities and mechanical properties as compared to the PDMS polymer prepared with tetraethoxysilane (TEOS). The observed improvements in thermal properties could be attributed to the effective three-dimensional network structures resulting from the structure of DVPS. The thermal decomposition of the RTV silicone rubbers in nitrogen was also monitored by TGA coupled with real-time FTIR, and the degradation residues were also characterized by FTIR. It was found that the POSS cross-linker facilitated the formation of cross-links in the degradation residues. The striking improvement in mechanical properties could be attributed to the synergistic action of the structure of three-dimensional multi-arm cross-linker (vinyl-POSS derivative), the plasticization of self-cross-linking Vinyl-POSS derivative and perfect distribution of vinyl-POSS derivative.     

Polyhedral oligomeric silsesquioxanes (POSS) thermal degradation

The mechanism of thermal degradation of several substituted polyhedral oligomeric silsesquioxanes (POSS) cages is studied in this work.Hydrogen POSS and methyl POSS shows incomplete sublimation on heating, both in inert atmosphere and in air. Isobutyl and octyl substituted POSS undergo an almost complete evaporation when heated in inert atmosphere. In air, oxidation competes with volatilization, producing a considerable amount of silica-like residue on heating up to 800 °C.Phenyl POSS shows a higher thermal stability than saturated aliphatic POSS and limited volatility, producing a ceramic residue at high yield on heating in nitrogen, composed of a silica containing a considerable amount of free-carbon. A lower amount of residue is shown after heating in air, corresponding to the POSS Si-O fraction.A vinyl POSS cage/network resin is also studied, in comparison to above materials, showing the highest ceramic yield.     

Co-flame retarding effect of ethanolamine modified titanium-containing polyhedral oligomeric silsesquioxanes in epoxy resin

A metal-doped organic and inorganic hybrid polyhedral oligomeric silsesquioxanes (POSS) with a titanium atom in the POSS cage and an ethanolamine substitute group in the corner, namely MEA-Ti-POSS, was synthesized through simple condensation reaction and substitute reaction. It was blended with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to form a kind of blending-type flame retardant system for the modification of epoxy resins. The thermal stability, flame retardancy and mechanical properties of cured epoxy resin composites were studied. Comparing with pure epoxy resin, the LOI value of EP/MEA-Ti-POSS/DOPO composites was raised from 25.2% to 32.7%, and the UL-94 grade reached V-0 level at a loading of the mixture of 5% MEA-Ti-POSS and 5% DOPO. In addition, the cone calorimetry results showed that the heat release rate, total heat release and total smoke production as well as smoke production rate were all reduced during the combustion of EP/MEA-Ti-POSS/DOPO composites. The residual char analysis revealed that carbon residues of EP/MEA-Ti-POSS/DOPO composite served as a physical protective layer to insulate the oxygen and combustible gases to reduce the ablation of the matrix. It was concluded that the mixture of MEA-Ti-POSS and DOPO not only effectively raised the thermal stability and flame retardancy of epoxy composited materials, but also improved their mechanical properties, which expanded a promising application of the metal-POSS derivatives as non-halogen additives in the flame retardant polymers.     

Glass transition and structural properties of glycidyloxypropyl-heptaphenyl polyhedral oligomeric silsesquioxane-epoxy nanocomposites

We have used molecular simulations to study the properties of nanocomposites formed by the chemical incorporation of polyhedral oligomeric silsesquioxane (POSS) particles in the cross-linked epoxy network. The particular POSS molecule chosen—glycidyloxypropyl-heptaphenyl POSS—can form only one bond with the cross-linker and thus was present as a dangling unit in the network. Four epoxy-POSS nanocomposites containing different fractions (up to 30 mass/%) of POSS particles were studied in this work. Well-relaxed atomistic model structures of the nanocomposites were created and then molecular dynamics simulations were used to characterize the density, glass transition temperature (T _g), and the coefficient of volume thermal expansion (CVTE) of the systems. In addition to the effect of nanoparticle loading, the effect of nanoparticle chemistry on the nanocomposite properties was also characterized by comparing these results with our previous results (Lin and Khare, Macromolecules 42:4319–4327, 2009) on neat cross-linked epoxy and a nanocomposite containing a POSS nanoparticle that formed eight bonds with the cross-linked network. Our results showed that incorporation of these monofunctional POSS particles into cross-linked epoxy does not cause a measurable change in its density, glass transition temperature, or the CVTE. Furthermore, simulation results were used to characterize the aggregation of POSS particles in the system. The nanofiller particles in systems containing 11, 20, and 30 mass/% POSS were found to form small clusters. The cluster-size distribution of nanoparticles was also characterized for these systems.     

双(环戊二烯基)二氯化锆催化合成乙烯-笼型倍半硅氧烷杂化共聚物及其结构表征

通过双(环戊二烯基)二氯化锆(Cp₂ZrCl₂)催化剂和改良的甲基铝氧烷(MMAO)助催化剂, 合成了无机-有机杂化共聚物. 研究了2种具有不同单乙烯基反应基团的笼型倍半硅氧烷(POSS)与乙烯的聚合. 对共聚产物的结构、 热力学性质、 分子量及其分布等进行了研究. 共聚单体(POSS)的插入率在0.01%~0.30%之间, 随着共聚单体在共聚物中摩尔分数的增大, 聚合物的熔点和熔解热降低. 共聚物的热重分析结果显示, 乙烯-POSS共聚物拥有更高的热分解温度以及较高的热分解残留量. 随着POSS的加入, 聚合物的分子量明显提高, 聚合物的分子量分布变宽.     

Thermal study of an epoxy system DGEBA (<Emphasis Type="Italic">n</Emphasis>=0)/mXDA modified with POSS

The thermal degradation of the epoxy system diglycidyl ether of bisphenol A (DGEBA n=0) and m-xylylenediamine (mXDA) containing different concentrations of polyhedral oligomeric silsesquioxanes (POSS) nanoparticles was studied by thermogravimetric analysis in order to determine the influence of both, the POSS concentration and the curing cycle on the degradation process and to compare it with the results for the non modified system. Glass transition temperatures for the same systems were also determined by differential scanning calorimetry. Different behaviors have been observed, depending on the POSS concentration and on the curing selection.     

Prediction of Heat Shield Performance in Terms of Epoxy Resin Structure

Abstract

High-strength, readily processable, char-forming, insulative materials are being sought for application in ablative heat shields for re-entry vehicles. Toward this end, the family of epoxy resins has been evaluated. The structure of epoxy resins and curing agents in terms of their functionality, aromaticity, and chemical nature is discussed in relation to its effect on ablative properties. The concept of controlled, constructive thermal degradation is extremely important in ablative epoxide compositions. Bridged Diels-Alder adducts based upon cyclic dienes and maleic anhydride perform well as epoxy resin curing agents in this respect. The mechanism of thermal ablative degradation of these systems is discussed in terms of in situ thermal control and char-forming reactions. The position of attachment of glycidyl groups, as well as the nature and position of other sub-stituents around the aromatic nucleus, has little effect in general upon the ablative properties of epoxy resins. Thermal and ablative data of both benzene and naphthalene derivatives are given. A new epoxy resin based upon 2-nitro resorcinol has been synthesized. This resin gives significant char increases, both quantitatively and qualitatively, over conventional epoxides. The unusual mechanism of polymerization and thermal degradation of this resin is discussed.     

Thermal and morphological characteristics of solution blended epoxy/NBR compound

Systematic study about the effect of acrylonitrile–butadiene rubber (NBR) concentration on the fracture toughness and thermal behavior of epoxy resin is conducted in this study. NBR is solved in an aromatic hydrocarbon solvent and is added to epoxy resin. We used diethylene-teriamin as the curing agent for epoxy resin. Tensile test results, performed followed by molding procedure, show that the toughness is improved owing to the increase of rubber content. Scanning electron microscopy (SEM) and atomic force microscopy besides thermogravimetric analysis (TG) are used to investigate the epoxy/rubber interface and chemical decomposition of the resultant mixture. The thermal behavior of cured epoxy resin was analyzed via TG instrument at different heating rates. Thermogravimetry curves showed that the thermal decomposition of epoxy system was occurred in only one stage regardless of the rubber content. The apparent activation energies of the rubber/epoxy systems containing 0, 5, and 10 phr of rubber were determined by Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Friedman methods. The results prove that the thermal stability of epoxy resin was decreased with enhancing the rubber content. However, the trend of changing activation energy versus conversions is totally different followed by adding the elastomer to the system compared to neat epoxy resin. Moreover, the results obtained via our proposed facile solution blending method are compared to those of resins modified with nano-powdered elastomer.