新型氮化硼陶瓷纤维先驱体——含硅聚硼氮烷的合成与表征

以三氯化硼、六甲基二硅氮烷为起始原料, 采用一步法合成了一种新型含硅氮化硼陶瓷纤维先驱体——含硅聚硼氮烷. 该法合成工艺简单, 且合成收率约为87%(质量分数). 采用元素分析、傅立叶红外光谱、核磁共振波谱、热机械分析、动态流变分析等对含硅聚硼氮烷的组成、结构和性能进行了表征. 结果表明, N—B为含硅聚硼氮烷先驱体的骨架结构, 其中, B, N主要以硼氮六环形式存在, 而Si则以Si—CH₃, Si—N形式存在. 该先驱体软化点为110 ℃, 具有优良的成型性, 在190 ℃的N₂气氛中可纺丝得到20～25 μm的有机纤维.     

基于环硼氮烷的高陶瓷产率SiBCN先驱体的合成与性能

聚合物先驱体转化法作为制备SiBCN陶瓷及其复合材料的重要途径,具有成型温度低、产物结构和组成可控等优点.设计合成合适的聚合物先驱体是提高陶瓷产率和性能的关键因素之一,本文采用三氯环硼氮烷(TCB)与乙炔基氯化镁进行反应,合成了乙炔基环硼氮烷,进而与二氯硅烷和二氯甲基乙烯基硅烷进行共氨解反应,制备了聚硼硅氮烷先驱体(PBSZ)并进行了高温裂解.采用综合热分析(TG-DSG)对其陶瓷化过程进行了分析,并采用XRD和SEM对陶瓷化产物的结构进行了表征.PBSZ在室温下是液态,易溶于二氯甲烷和氯仿等溶剂,可加工性优良.基于PBSZ先驱体的SiBCN陶瓷产率超过80%;陶瓷化产物在1400℃以下为无定形状态,在1500℃可形成由α-Si3N4,β-Si3N4,h-BN和SiO2晶体结构组成的陶瓷;陶瓷产物表面致密平整且具有优异的热稳定性和氧化性能,表明聚硼硅氮烷(PBSZ)有望成为高陶瓷产率和高性能陶瓷的重要先驱体.     

聚硼硅氮烷的合成及其流变性能研究

以二氯甲基硅烷、三氯化硼、六甲基二硅氮烷为起始原料,采用缩聚法合成了一种新型SiBNC陶瓷先驱体-聚硼硅氮烷(PBSZ)。通过调节原料二氯甲基硅烷的用量可获得不同软化点的先驱体。通过改进的毛细管流变仪,首次对熔融纺丝状态时聚硼硅氮烷(PBSZ)的流变特性展开了研究。结果表明：PBSZ熔融纺丝时,剪切速率在10～110s-1时,为切力变稀流体。非牛顿指数为0.83～0.90,粘流活化能约为142KJ/mol,表观粘度440～2460Pa·s,PBSZ对温度变化的敏感性较聚碳硅烷小,可纺温区较宽。PBSZ纺丝性能良好,纤维连续无断头长度﹥1600m,纤维直径﹤20μm。     

甲胺/二甲胺共取代合成氮化硼先驱体聚硼氮烷

将三氯环硼氮烷(TCB)与甲胺/二甲胺进行共胺解取代反应, 首先制得了不同胺基的取代单体, 经过进一步热聚合反应合成了聚硼氮烷先驱体. 通过对不同单体的聚合产物组成与结构分析, 探讨了不同取代基对热聚合反应及产物结构的影响. 研究表明, 当控制甲胺/二甲胺摩尔比为1∶2, 聚合温度180 ℃, 获得的聚硼氮烷数均分子量为7603, 分子量分散系数为1.80, 熔点为83 ℃, 组成为BC_0.76N_1.39H_2.5, 该聚合物具有近似线性分子结构, 表现出优良的可纺性, 可制得平均直径10～15 μm的先驱体纤维, 为制备氮化硼纤维奠定了基础.     

聚硼硅氮烷的表征及其流变性能

以二氯甲基硅烷、三氯化硼、六甲基二硅氮烷为起始原料,采用缩聚法合成了新型SiBNC陶瓷前驱体--聚硼硅氮烷(PBSZ),其产率达90%. 通过调节二氯甲基硅烷的用量可获得不同软化点的前驱体. 采用改进的毛细管流变仪,首次对熔融纺丝状态时PBSZ的流变特性进行了研究. 结果表明,PBSZ熔融纺丝时,剪切速率在10～110 s~(-1)范围内时,为切力变稀流体,非牛顿指数为0.83～0.90,表观粘度为440～2 460 Pa·s,粘流活化能约为142 kJ/mol. PBSZ纺丝性能良好,纤维连续无断头长度＞1 600 m,纤维直径＜20 μm.     

胺源对“一锅法”合成聚硼硅氮烷结构及性能的影响

以六甲基二硅氮烷(MM^N)、四甲基二乙烯基二硅氮烷(MM^NVi)和四甲基二硅氮烷(MM^NH) 3种不同结构的二硅氮烷为胺源,通过与氯硅烷和三氯化硼反应,制备出具有不同封端结构的聚硼硅氮烷.其中,以MM^N、MM^NVi为胺源可获得液态产物;以MM^NH为胺源时,因合成过程中发生活性基团间的过度交联导致产物凝胶.采用核磁共振波谱仪、红外光谱仪对液态前驱体聚合物及其热解产物的结构进行了表征.研究结果表明：通过“一锅法”制备的液态聚硼硅氮烷主链具有较多的支化和环状结构,随着封端结构中乙烯基含量的增加,所得前驱体的固化温度降低,固化反应活化能降低.与以MM^N为胺源和封端剂合成的聚硼硅氮烷相比,以MM^NVi为胺源所得前驱体固化前后陶瓷产率分别提高了14.9%及8.1%.并且,通过改变胺源的种类和比例可以调节热解产物的元素组成,合成的液态前驱体聚合物热解所得SiBCN陶瓷结晶温度高于1700℃.     

高硼含量的SiC陶瓷先驱体的合成和表征

采用经典硼氢化反应, 通过硼烷二级硫醚(BH₃·SMe₂)与二甲基二乙烯基硅烷(DVS)反应, 合成了聚硼碳硅烷(PBCS)陶瓷先驱体, PBCS在氮气中经高温裂解得到了高硼含量的SiC陶瓷.利用红外光谱、核磁共振波谱和热重分析对聚合物的结构和性能进行了表征; 利用元素分析、X射线衍射和扫描电子显微镜对聚合物的裂解产物进行了分析.结果表明, 聚合物的结构中含有B—C, Si—C和C—H键, 在1000℃氮气气氛中, 其陶瓷产率在50%以上.陶瓷产物在1100℃以无定形态存在, 硼含量高达6.46%, 在1300℃时出现明显结晶, 形成B₂O₃, C和β-SiC三相组成的多元复相陶瓷, 在1500℃以下陶瓷产物表面光滑, 结构致密.     

聚硼硅氮烷陶瓷前驱体分子结构设计和合成*

聚硼硅氮烷是制备高性能硅硼 碳氮（SiBCN）复相陶瓷的主要聚合物前驱体,在耐高温、抗氧化高性能陶瓷领域中具有重要的研究价值。本文分4个方面,即基于硼吖嗪的聚硼硅氮烷、侧基含有环硼氮烷或单硼烷的聚硼硅氮烷、基于多官能硼烷构筑的聚硅氮烷和含硼聚硅基碳化二亚胺,从聚硼硅氮烷分子结构设计、改性、合成及在多维尺寸材料中初步应用的角度综述了该领域国内外研究的新进展,指出了聚硼硅氮烷陶瓷前驱体设计合成研究发展中值得关注的新方向。     

紫外光固化含硼氮六环的硅硼氮碳烷陶瓷单源先驱体的合成、表征及性能研究

以氯甲基三氯硅烷、三氯化硼和六甲基二硅氮烷为原料经过一步法合成出一种新型的端基为Si-Cl 基团的含硼氮六环的硼硅氮碳烷单体: B,B',B"-三[(三氯硅基)-亚甲基]环硼氮烷(TSMB), 用2-羟基丙烯酸乙酯和乙烯基乙二醇醚对TSMB 进行功能化改性, 得到可UV 固化的陶瓷单源先驱体a-TSMB 和e-TSMB; a-TSMB 和e-TSMB 经UV 固化、1400℃下裂解2 h 最后制备出陶瓷材料C1 和C2. 采用红外光谱(FT-IR)、核磁共振波谱(NMR)、等温差示光量热分析(DPC)、实时红外光谱(RT-IR)、热失重分析(TGA)、X 射线光电子能谱(XPS)和X 射线衍射法(XRD)分别对TSMB, e-TSMB 和a-TSMB 以及陶瓷C1 和C2 的结构、组成、UV 反应性、陶瓷产率和耐高温性能进行了研究. 结果表明: a-TSMB 和e-TSMB 两种陶瓷单源先驱体分子中含有硼氮六环结构, 分子末端为丙烯酸酯或乙烯基醚官能团, 与理论设计完全相符; a-TSMB 和e-TSMB 的光聚合反应在25 s 内分别完成82%和67%, 最终双键转化率可达到90.0%和74.0%, 其陶瓷产率在1300 ℃时为57.9%和48.5%; 陶瓷材料C1 和C2 中含有Si, B, C, N, O 五种元素, 且B 元素的含量达到4.4%和4.9%, 达到耐高温陶瓷对B 元素含量的要求, 在1400 ℃时陶瓷C1 和C2 均可保持非晶态具有优异的耐高温性能.     

含硅聚硼氮烷裂解转化制备氮化硼陶瓷纤维

以低活性含硅聚硼氮烷为先驱体,经熔融纺丝,BCl₃脱硅不熔化处理以及在氨气气氛中高温裂解制备的氮化硼纤维仍含有硅元素,这主要是含硅聚硼氮烷结构中的B-N(SiMe₃)₂和B-N(SiMe₃)-B由于位阻与BCl₃反应脱除SiMe₃不完全所致.而采用HCl首先与含硅聚硼氮烷反应减少其位阻,再通过BCl₃进一步脱硅不熔化处理制备的氮化硼陶瓷纤维经FT-IR、X射线衍射(XRD)分析表明纤维基本不含硅元素,并且扫描电子显微镜(SEM)表明得到的氮化硼陶瓷纤维直径约为11μm,断面致密无孔,室温下抗拉强度为0.45GPa.     

Synthesis and Characterization of Silazane-Based Polymers as Precursors for Ceramic Matrix Composites

The goal of this investigation was to optimize the synthesis of silazane-based polymers for processing fibre-reinforced ceramic matrix composites (CMCs). Liquid oligomeric silazanes were synthesized by ammonolysis of chlorosilanes and characterized spectroscopi- cally (FTIR, NMR) as well as by elemental analysis. The silazanes were obtained in high yield and purity. Different functional groups (system S1: Si—H, Si—CH₃, Si—CH=CH₂) and different degrees of branching in the Si—N backbone [system S2; Si(NH)₃, Si(NH)₂] were realized in order to study the properties of the silazanes that are dependent on the molecular structure. For processing ceramics via pyrolysis of pre-ceramic oligomers, molecular weight, rheological behaviour, thermosetting and ceramic yield were investigated systematically and correlated with the molecular structure of the silazanes. Low molecular weights (500–1000 g mol⁻¹) as well as low viscosity values (0.1–20 Pa s) enable processing of the silazanes in the liquid phase without any solvent. Due to the latent reactivity of the functional groups, curing of the polymers via hydrosilylation is achieved. Structural changes and weight loss during polymer curing as well as the organic/inorganic transition were monitored by FTIR spectroscopy and differential thermogravimetric analysis. With increasing temperature (room temperature to 800 °C) the hydrogen content decreases from 7 to < 0.5 wt% due to the formation of gaseous molecules (NH₃, CH₄, H₂). High ceramic yields up to 80% were reached by branching the oligomers, thus reducing the amount of volatile precursor fragments. Up to 1300 °C, ceramic materials remained amorphous to X-rays. At higher temperatures (1400–1800 °C) either SiC or SiC/Si₃N₄ composites were selectively crystallized, depending on the pyrolysis conditions. The utility of the optimized precursors for CMCs has been demonstrated by infiltration of fibre preforms and subsequent pyrolysis. © 1997 by John Wiley & Sons, Ltd.     

Functionalization and further crosslinking of the nicalon polycarbosilane based on its metalation with the n-butyllithium—postassium t-butoxide reagent

Reaction of the Nicalon polycarbosilane with the n-BuLi/Me₃COK reagent resulted in metalation of approximately one CH₂ group in four. Reaction of the metalated polymer with Me₂ (CH₂ = CH)SiCl gave a Me₂(CH₂ = CH)Si-substitued Nicalon polycarbosilane. The polymer was heated with different amounts of the [(MeSiH)_～0.8(MeSi)_～0.2]_n polysilane in the presence of azobisisobutyronitrile in refluxing benezene. Hydrosilylation by the Si? H-containing polysilane of the CH₂?CH groups of the Me₂(CH₂?CH) Si-substituted Nicalon polycarbosilane gave a new hybrid polymer (when appropriate quantities of reactant polymers were used) whose pyrolyis in a stream of argon to 1000°C left a ceramic residue in 77% yield whose elemental analysis indicated a nominal composition of 91% by weight SiC and 9% C.     

CHEMOENZYMATIC SYNTHESIS OF BIODEGRADABLE POLY(1’-O-VINYLADIPOYL-SUCROSE)

t A novel polymer containing the sucrose group was synthesized by radical polymerization from an enzymaticallyprepared monomer, l'-O-vinyledipoyl-sucrose (VAS). Transesterification reaction of sucrose with divinyl adipate inanhydrous pyridine catalyzed by an alkaline protease from Bacillus subtilis at 60℃ for 7 days gave VAS (yield 55%) withoutany blocking/deblocking steps. The vinyl sucrose ester could be polymerized with potassium persulfate and H_2O_2 as initiatorto give poly(l'-O-vinyladipoyl-sucrose) with M_n = 33,000 and M_w = 53,200, M_w/M_n = 1.61. The polymer was biodegradable.After 6 days in aqueous buffer (pH 7), this alkaline protease could degrade poly(l'-O-vinyladipoyl-sucrose) to M_n of ca.1080, M_w/M_n = 3.30 (37℃), and M_n of ca. 5200, M_w/M_n = 2.44 (4℃). The polymer containing the sucrose branch would be afunctional material in various application fields.     

Some further observations on polymethylsilane as a precursor for silicon carbide

Poly(methylsilanes) produced by sodium coupling of methyldichlorosilane (2:1 molar ratio) contain residual chlorine which can be removed by reduction with LiAlH₄ at low temperature. Following this reduction, the polymers contain catalytically active centers (presumed to be silyl anions) which, in THF solution, further polymerize and crosslink the polymer at room temperature, while in toluene solution they are inactive. The reduced polymethylsilane gives high yields (ca 75%) of ceramic product on pyrolysis, but the composition is rich in silicon, compared with pure silicon carbide (SiC). Addition of catalytic amounts of dimethylzirconocene (DMZ) to this polymer gives a product which pyrolyzes to a product with stoichiometry close to that of SiC. It is concluded that the DMZ has an important influence in promoting Si–C bond formation, relative to Si–Si bond formation, during the pyrolysis.     

先驱体转化法制备Si-B-N-C陶瓷纤维及表征

以聚硼硅氮烷为先驱体, 经熔融纺丝、不熔化处理及氮气中高温热解、烧结得到Si-B-N-C陶瓷纤维. 利用元素分析、FTIR、XRD、高温热重分析等手段对Si-B-N-C纤维的组成、结构以及高温稳定性和抗氧化性等进行了表征. 结果表明, 纤维主要由Si3N4, BN和SiC等相组成, 其室温抗拉强度为2.1 GPa, 弹性模量为230 GPa, 具有很好的非晶稳定性和高温抗氧化性, 惰性气氛中可保持非晶至1700 ℃, 空气中加热至1100 ℃以下时无增重, 在1100-1400 ℃温度范围内增重约3.3％.     

Macroporous SiC?MoSi2 ceramics from templated hybrid MoCl5–polymethylsilane

A molybdenum‐containing preceramic polymer, MoPMS, was synthesized for the first time by HCl elimination of polymethylsilane (PMS) and MoCl₅ at room temperature in tetrahydrofuran. The insoluble MoPMS prepared was embedded into the void spaces of a silica colloidal crystal template within the pot life of the polymer and successfully transformed to a three‐dimensionally long‐range‐ordered macroporous SiC? MoSi₂ ceramic after pyrolysis at 1400 °C in an argon atmosphere followed by template removal in HF. The bead‐inverse macroporous SiC? MoSi₂ ceramic, with a ceramic yield of about 88%, exhibits high temperature stability, high BET surface area, and semiconducting behavior. In addition, the macroporous SiC? MoSi₂ ceramic was used as a catalyst carrier for platinum–ruthenium coated on the surface of the pores. The preceramic polymer and the ceramic were characterized by IR, thermogravimetric analysis, X‐ray diffraction, scanning and transmission electron microscopy, and BET surface area. Copyright © 2005 John Wiley & Sons, Ltd.     

Synthesis of Poly(silyne-co-hydridocarbyne) for Silicon Carbide Production

Pre-ceramic polymers have previously been shown to be polymeric precursors to silicon carbide, diamond and diamond-like carbon. Here, we report the synthesis of a pre-ceramic polymer, poly(silyne-co-hydridocarbyne), which was electrochemically synthesized from one monomer containing both silicon and carbon in its structure. The polymer is soluble in common solvents such as CHCl₃, CH₂Cl₂ and THF. Since the polymer contains both silyne and carbyne on its backbone, it can be easily converted to silicon carbide upon heating under an ambient inert atmosphere, or to SiO₂ under ambient air atmosphere. Poly(silyne-co-hydridocarbyne) was characterized with UV/Vis spectroscopy, FTIR, ¹H-NMR, GPC and Raman spectroscopy. Conversion of the polymer to SiC ceramic was accomplished by heating at 1000 and 750°C under an argon atmosphere and characterized with optical microscopy, SEM, X-Ray and Raman spectroscopies.