Delaminated zeolite‐catalysed synthesis of high‐molecular weight polycarbosilane as a low shrinkage SiC precursor

A polycarbosilane (PCS) with a higher number–average molecular weight (2710 vs. 1570), and hence with a higher ceramic yield (74 vs. 68%), compared to a commercial Nipusi type S PCS has been synthesized via the catalytic decomposition of polydimethylsilane at 400 °C using H‐ITQ‐2, a delaminated zeolite with a very high external surface area, as a solid acid. The silicon carbide film fabricated using this PCS was found to show a much lower level (16 vs. 39%) of shrinkage than the commercial PCS‐derived film, together with better mechanical properties, suggesting the potential of its preceramic polymer to produce robust ceramic coatings. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 725–732, 2008     

Preparation of a cross-linked polycarbosilane and its conversion to silicon carbide ceramics

Summary Cross-linked polycarbosilanes are obtained from the reaction of Cl₂MeSiCHCl₂ and Mg in tetrahydrofuran, followed by reduction with LiAlH₄. Analysis by NMR spectroscopy shows that most polycarbosilane is of the formula [MeSiCH]_n.Contribution no. 6627     

Synthesis and pyrolysis of a novel preceramic polymer PZMS from PMS to fabricate high‐temperature‐resistant ZrC/SiC ceramic composite

As a valuable ultra‐high‐temperature ceramic (UHTC), ZrC was introduced to SiC ceramic for the preparation of high‐temperature‐resistant ZrC/SiC composite by a polymer‐derived method through the reaction between Cp₂Zr(CH=CH₂)₂ and polymethylsilane (PMS). The composition, structure, element distribution and pyrolysis process of the preceramic polymer polyzirconomethylsilane (PZMS) were investigated by nuclear magnetic resonance, infrared, gel permeation chromatography, X‐ray photoelectron spectroscopy, energy‐dispersive X‐ray spectroscopy, scanning electron microscopy and thermogravimetric analysis. The obtained ZrC/SiC ceramic composites had very good high‐temperature resistance with a weight loss of 7.1% after being subjected to temperatures ranging from 1200 to 2200°C, as the introduction of ZrC prevented the fast growth of crystalline β‐SiC. The ceramic composites prepared by this method were homogeneous with well‐distributed element components, and the ceramic yield reached as high as 78.4%. Copyright © 2013 John Wiley & Sons, Ltd.     

Cyclosilazanes and borazines: polymer precursors to silicon‐ and boron‐containing ceramics

The chemistry of cyclosilazanes and borazines is a topic of current interest in view of preceramic polymers which yield on pyrolysis various useful ceramic materials, e.g. silicon and boron carbide, silicon and boron nitride, and ternary or quaternary mixtures of these materials. These materials are hard and have high oxidative and thermal stability. Other useful properties are resistance to corrosion, thermal shock and creep, low electrical conductivity and low coefficient of thermal expansion. One of the best application prospects is the use of the preceramic polymers as protective coating material for carbon fibres. Copyright © 2000 John Wiley & Sons, Ltd.     

三维有序SiC空心球的制备及表征

以三维有序多孔碳为模板, 以聚甲基硅烷(PMS)为前驱体, 经过前驱体的渗入、交联和陶瓷转化以及多孔碳模板的烧除, 制备了长程三维有序SiC空心球. 所制备的SiC空心球的外径(135-896 nm)、 球壳厚度(14-79 nm)、 BET比表面积(50.8～5.0 m2/g)及微孔体积(0.265～0.038 cm3/g)受不同孔径的多孔碳模板(150-1 000 nm)或不同前驱体浓度的控制. 所制备的SiC空心球以hcp结构排列成长程三维有序的序列.     

三维有序多孔图案化SiC陶瓷的制备

结合毛细管微模塑技术、模板技术和先驱体转化技术, 以图案化聚二甲基硅氧烷(PDMS)弹性体为模具,以氧化硅凝胶小球为模板, 以液态聚碳硅烷(PCS)为先驱体, 经过氧化硅凝胶小球图案化模板的形成, 先驱体的渗入, 模板中先驱体的交联, 弹性模具的去除, 图案化先驱体的无机化和模板的去除, 制备了图案化多孔SiC 陶瓷.研究结果表明：所制备的图案化多孔陶瓷中, 图案的尺寸受图案化PDMS 弹性模具的控制, 球形孔的孔径可由氧化硅凝胶小球来调节. 图案化陶瓷中球形孔不仅三维有序排列, 而且由于模板中小球的相互接触形成的“窗 口”使球形孔三维贯通.     

9,10‐Dihydro‐9,10‐diboraanthracene: Supramolecular Structure and Use as a Building Block for Luminescent Conjugated Polymers

Building bridges : The title compound forms an unprecedented polymeric structure with bridging B–H–B three‐center two‐electron bonds in the solid state. This organoborane serves as an efficient precursor for the preparation of boron‐doped π‐conjugated polymers by hydroboration polymerization with a functionalized 1,4‐diethynylbenzene (see picture). These polymers form thin films that show intense green luminescence.

     

Development of novel flame‐retardant thermosets based on boron‐modified phenol–formaldehyde resins

Boron‐containing novolac resins were prepared through the modification of a commercial novolac resin with different contents of bis(benzo‐1,3,2‐dioxaborolanyl) oxide. Their thermal and flame‐retardant properties were measured. Then, they were crosslinked with hexamethylenetetramine, and their thermal, thermodynamomechanical, and flame‐retardant properties were evaluated. Their modification degree was related to the segmental motion of the materials. The crosslinking of the boron‐modified novolac resins with hexamethylenetetramine was slower and not as extensive as that of commercial novolac resins because the nitrogen from intermediate species coordinated with boron. The thermal degradation of the boron‐containing novolac resins generated boric acid at high temperatures and gave an intumescent char that slowed the degradation and prevented it from being complete. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3503–3512, 2006     

Synthesis and ceramic conversion of a new oligomeric precursor to boron nitride

A new polyaminoborazine with good solubility was synthesized by ammonolysis reaction of a mixture of B‐chloroborazine, B‐bischloroborazine, and B‐trichloroborazine under mild condition. The oligomer was easily cured at 250°C. The pyrolytic residue of the cured oligomer was investigated with X‐ray photoelectron spectroscopy (XPS), powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA). The results indicated that crystalline h‐BN with B/N ratio of 1:1.01 is main in the residue pyrolyzed at 1500°C. Copyright © 2010 John Wiley & Sons, Ltd.     

Enhancement of the thermal and mechanical properties of a surface‐modified boron nitride–polyurethane composite

Thermoplastic polyurethane (PU) elastomer, prepared from poly(tetramethylene glycol) and methyl diphenyl diisocyanate, was blended with boron nitride (BN) to fabricate a thermally conductive interface material. BN treated by a silane coupling agent (BN―NH₂) and PU‐grafted BN were prepared to fabricate a composite that has better thermal conductivity and mechanical strength. The surface‐modified filler showed enhanced dispersibility and affinity because of the surface treatment with functional groups that affected the surface free energy, along with the structural similarity of the doped crystallized diisocyanate molecule with the matrix. The thermal conductivity increased from 0.349 to 0.467 W mk^?1 on 20 wt% PU‐grafted BN loading that is a 1.34‐fold higher value than in the case of pristine BN loading at the same weight fraction. Moreover, the number of BN particles acting as defects, thereby reducing the mechanical strength, is decreased because of strong adhesion. We can conclude that these composite materials may be promising materials for a significant performance improvement in terms of both the thermal and mechanical properties of PU‐based polymers. Copyright © 2014 John Wiley & Sons, Ltd.     

Syntheses and Characterization of New Vinyl‐Borylene Complexes by the Hydroboration of Alkynes with [(μ3‐BH)(Cp*RuCO)2(μ‐CO)Fe(CO)3]

Room temperature photolysis of a triply‐bridged borylene complex, [(μ₃‐BH)(Cp*RuCO)₂(μ‐CO)Fe(CO)₃] ( 1 a ; Cp*=C₅Me₅), in the presence of a series of alkynes, 1,2‐diphenylethyne, 1‐phenyl‐1‐propyne, and 2‐butyne led to the isolation of unprecedented vinyl‐borylene complexes (Z)‐[(Cp*RuCO)₂(μ‐CO)B(CR)(CHR′)] ( 2 : R, R′=Ph; 3 : R=Me, R′=Ph; 4 : R, R′=Me). This reaction permits a hydroboration of alkyne through an anti ‐ Markovnikov addition. In stark contrast, in the presence of phenylacetylene, a metallacarborane, closo‐[1,2‐(Cp*Ru)₂(μ‐CO)₂{Fe₂(CO)₅}‐4‐Ph‐4,5‐C₂BH₂] ( 5 a) , is formed. A plausible mechanism has been proposed for the formation of vinyl‐borylene complexes, which is supported by density functional theory (DFT) methods. Furthermore, the calculated ¹¹B NMR chemical shifts accurately reflect the experimentally measured shifts. All the new compounds have been characterized in solution by mass spectrometry and IR, ¹H, ¹¹B, and ¹³C NMR spectroscopies and the structural types were unequivocally established by crystallographic analysis of 2 , 5 a , and 5 b .     

Synthesis of soluble and meltable pre‐ceramic polymers for Zr‐containing ceramic nanocomposites

Polymer‐derived methods are one of the most important tools for the synthesis of ceramics with a finely dispersed microstructure. In this study, a soluble and meltable ZrC/C pre‐ceramic polymer, P‐DACZ, (which would later exhibit a high ceramic yield of 71 wt%) was synthesized via radical polymerization. By adding low molecular weight polycarbosilane in any proportion during the radical polymerization process of P‐DACZ, a soluble and meltable ZrC/SiC/C pre‐ceramic precursor, PCS‐DACZ (which would later exhibit a high ceramic yield of >80 wt%) was synthesized. After annealing at 1400 °C under an argon flow, the precursors converted into bulk ZrC/C and ZrC/SiC/C ceramic nanocomposites. The ZrC nanoparticles could resist any grain growth when heat‐treated at temperatures above 1800 °C because the C or SiC matrix prevented long‐range atomic diffusion of zirconium. Such ceramic nanocomposites would be suitable for structural and (multi)functional applications at harsh environments with high temperatures.     

二氧化硅修饰纳米氧化锆陶瓷材料的制备及性能

以二甲基二乙氧基硅烷为硅源,在水溶液中成功制备了SiO2修饰纳米ZrO2颗粒;利用透射电子显微镜、热重分析仪、X射线衍射仪、红外光谱仪分析了样品的形貌和结构;将SiO2/ZrO2与α-Al2O3制成陶瓷材料,考察了其机械性能.结果表明,所制备的SiO2/ZrO2晶粒均一,直径约为10nm,硅原子在SiO2/ZrO2中以Si―O―Zr键合形式存在,SiO2不影响ZrO2的晶型.引入SiO2使得ZrO2晶粒细化、尺寸均匀性提高;SiO2/ZrO2/Al2O3陶瓷气孔率小,具有致密的显微结构和优异的机械性能.     

Rf‐GDOES analysis of composite metal/ceramic electroplated coatings with nano‐ to microceramic particles' size: issues in plasma sputtering of Ni/micro‐SiC coatings

Ni matrix composite coatings reinforced with nano‐ and microceramic particles were analyzed by radio frequency glow discharge optical emission spectrometry (Rf‐GDOES). An interesting phenomenon related to the sputtering and excitation modes of this technique was observed. During plasma sputtering with Rf‐GDOES, the micro‐SiC particles were detached from metal matrix and did not contribute to the analytical signals. The same was not found in composite coatings containing nanoceramic particles. This anomalous behavior was confirmed by atomic force microscopy (AFM) investigation and scanning electron microscope (SEM) observations into Rf‐GDOES craters that showed the presence of residual non‐sputtered microparticles. Various attempts were done in order to minimize this problem, mainly by varying the analysis parameters of the used instrumentation, but without any relevant success. Some suggestions were then proposed for explaining the observed phenomenon, moreover possible solutions (e.g. by using a strong magnetic field or changing plasma gas to be more energetic) are discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Mechanism and characterization of alkylene‐ and p‐ethylenebenzylene‐spaced polycarbosilanes ceramic precursor synthesized by electropolymerization

An electropolymerization of haloalkylhalosilanes (Cl? R? SiCH₃Cl₂) that possess two types of electroactive sites, that is, the C? Cl and Si? Cl bond is described. The one‐pot synthesis method is shown to yield branched polycarbosilanes having a regular carbon block‐spaced silicon backbone structure. A series of branched polycarbosilanes, [? R? SiCH₃? ]_n with R being ? CH₂? , ? C₂H₄? , ? C₃H₆? , and ? CH₂? C₆H₄? C₂H₄? , have been successfully electropolymerized with M_n up to 42,600 Dalton. Experimental and simulation cyclic voltammetry of these monomers and the computational examination of their LUMOs are applied to study the electropolymerization mechanism. The results suggest that polymerization proceeds by iterating steps involving (1) electroreduction of a C? Cl bond to a carbanion, which is catalyzed by silylanion radical [Cl SiCl(CH₃)RCl] and/or Ni(0)/TDA‐1; and (2) nucleophilic attack of carbanions to Si? Cl bonds of a second monomer or oligomer to extend the polymer chain. The investigation reveals that the R spacer has a considerable impact on the polymerizability of the corresponding monomer. Such interfacial polymerization resembles a template polymerization, leading to unique microstructures that were preserved even after converted to silicon carbide ceramics at high temperatures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7677–7689, 2008     

Synthesis of novel boron‐containing epoxy–novolac resins and properties of cured products

Epoxy–novolac resins were synthesized by modifying a commercial novolac resin with epichlorohydrin. These epoxy–novolac resins were characterized and further modified with different contents of bis(benzo‐1,3,2‐dioxa‐borolanyl)oxide or bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxa‐borolanyl)oxide. The boron‐containing epoxy–novolac resins were autocatalytically crosslinked or crosslinked with BF₃MEA and their thermal stability and flame retardancy were determined by thermogravimetric analysis and limiting oxygen index (LOI) values. These LOI values for the bis(benzo‐1,3,2‐dioxa‐borolanyl)oxide derivatives were higher than the boron‐free novolac resins, which shows the benefit of the presence of boron. To test the role of boron in the enhancement of flammability, scanning electronic microscopy and energy‐dispersive X‐ray spectroscopy images were made. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6332–6344, 2006     

Synthesis,polymerization, and effects on the flame retardancy of boron‐containing styrenic monomers

A boron‐containing styrenic monomer, 5‐benzyl‐2‐phenyl‐5‐(4‐vinylbenzyl)‐[1,3,2]‐dioxaborinane, was synthesized to study the influence of boron on the properties of the homopolymer and copolymer with styrene. A similar monomer without boron was also prepared and polymerized so that the properties of its polymer could be compared with the aforementioned boron‐containing polymers. These monomers were characterized by elemental analysis, mass spectrometry, Fourier transform infrared, and ¹H and ¹³C NMR. The thermal degradation of boron‐containing styrenic polymers was studied by means of Fourier transform infrared, which showed the presence of boric acid as char. The flame‐retardant effect was assessed by the measurement of the limiting oxygen indices and char yields during heating in nitrogen and air. The boron‐containing polymers had higher limiting oxygen indices and gave greater yields of char than those without boron. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem43: 6419–6430, 2005     

Novel flame‐retardant thermosets: Diglycidyl ether of bisphenol A as a curing agent of boron‐containing phenolic resins

Boron‐containing novolac resins were synthesized by the modification of a commercial novolac resin with different contents of bis(benzo‐1,3,2‐dioxaborolanyl)oxide. These novolac resins were crosslinked with diglycidyl ether of bisphenol A (DGEBA), and their thermal, thermodynamomechanical, and flame‐retardant properties were evaluated. The boron‐containing novolac resins were less thermally stable than the unmodified novolac resin. Their modification degree and DGEBA content were related to the crosslinking density of the materials. The boron‐containing novolac resins generated boric acid at high temperatures and gave an intumescent char that slowed down the degradation and prevented it from being total. They also showed good flame‐retardant properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1701–1710, 2006     

Synthesis and characterization of a novel precursor‐derived ZrC/ZrB2 ultra‐high‐temperature ceramic composite

ZrC and ZrB₂, two valuable members of ultra‐high‐temperature ceramics (UHTCs), are potentially useful as structural materials in aerospace engineering and hypersonic flight vehicles. This work focused on the preparation of ZrC/ZrB₂ UHTC composite by employing a precursor‐derived method. The precursor polymer PZCB was synthesized by the reaction between Cp₂Zr(CH═CH₂)₂ and borane. The composition, structure, element distribution and pyrolysis process of PZCB were investigated by NMR, IR, X‐ray photoelectron spectroscopy, scanning electron microscopy and TGA. The ceramic yield was 50% and the obtained well‐distributed ZrC/ZrB₂ ceramic composites had very good high‐temperature resistance. Copyright © 2012 John Wiley & Sons, Ltd.