聚碳硅烷/二乙烯基苯陶瓷前驱体交联样品的制备

研究了聚碳硅烷交联样品的制备过程，着重讨论了用二乙烯基苯交联聚碳硅烷的条件。结果表明：选择熔点为200℃，摩尔质量为1500g/mol作为熔融纺丝，生产碳化硅纤维前驱体用的聚碳硅烷，以二乙烯基苯为交联剂，氯铂酸异丙醇溶液为催化剂，聚碳硅烷与二乙烯基苯的质量比不能低于1：0．2，二乙烯基苯的用量为20％－40％，交联反应温度120℃时，制成的聚碳硅烷／二乙烯基苯陶瓷前驱体交联样品性能良好。     

聚钽碳硅烷陶瓷先驱体的制备与表征

为了提高SiC陶瓷纤维的综合性能,利用聚二甲基硅烷热解制得的产物液态聚硅烷(LPS)与五氯化钽(TaCl5)反应,制得含钽SiC陶瓷纤维的先驱体聚钽碳硅烷(PTCS).研究表明,反应过程中存在LPS的裂解重排反应,Si-H键在反应中显示出很高的活性,PTCS摩尔质量的增加是LPS形成的Si-H键与TaCl5发生交联反应的结果,用LPS与TaCl5为原料不但能够使钽元素成功地引入到先驱体中并分布均匀,而且由于其成本比其它原料相对低廉,便于大批量合成.     

液态聚硼硅氮烷的陶瓷化过程

采用Fourier红外光谱、热重–差热以及X射线衍射分析对新型液态SiBNC先驱体进行了结构表征,重点研究了先驱体的陶瓷化过程。结果表明：先驱体以—CH3和—CH=CH2为侧链基团,含有C—H、C=C、Si—H、B—N、N—H、Si—N等化学键;N2气氛保护下的陶瓷产率约为85%,质量损失主要发生在300～800℃;随着温度的升高,聚合物中有机基团逐渐减少,900℃完成无机化转变,得到含有自由碳的非晶态SiBNC陶瓷,1200℃以上非晶态SiBNC陶瓷开始晶化,1500℃得到由C、SiC、Si3N4和BN组成的复相陶瓷。     

液态聚碳硅烷制备含铝碳化硅陶瓷前驱体——聚铝碳硅烷

通过液态聚碳硅烷与乙酰丙酮铝反应,合成了一系列的聚铝碳硅烷,考察了原料配比和反应温度的影响.结果显示:改变合成温度或乙酰丙酮铝的加入量,聚铝碳硅烷呈现从液态到固态的转变.增加乙酰丙酮铝的配比或提高合成温度,可增加聚铝碳硅烷中铝的质量分数,在360℃合成的产物中铝的质量分数接近理论值;增加铝的质量分数或提高合成温度,可增大聚铝碳硅烷的分子量及其多分散系数.360℃以下聚铝碳硅烷的数均分子量随着铝的质量分数的增加呈线性增加.红外光谱及核磁共振分析结果均显示,铝元素的引入伴随着Si-H键的消耗,通过AlO_x(x=4,5,6)基团使液态聚碳硅烷分子部分交联长大,高铝含量的样品具有较高的交联程度.     

SiC(Nb)陶瓷纤维先驱体聚铌碳硅烷的合成与表征

为了提高SiC陶瓷纤维的综合性能,利用聚二甲基硅烷热解制得的产物液态聚硅烷(liquid polysilane,LPS)与五氯化铌(NbCl5)反应,制各了含铌SiC陶瓷纤维的先驱体聚铌碳硅烷(polyniobiumcarbosilane,PNCS).研究表明:反应过程中存在LPS裂解重排反应,Si-H键在反应中显示出很高的活性,FNCS分子量的增加是LPS形成的Si-H键与NbCl5发生交联反应的结果,用LPS与NbCl5为原料不但能使铌元素成功地引入到先驱体中并且分布均匀,而且由于其成本比其他原料相对低廉便于大批量合成.利用PNCS制备的Si-Nb-C-O陶瓷纤维平均强度为1.8GPa,平均直径为12 μm,耐高温性能优异.     

聚碳硅烷的结构和形态

通过GPC-VPO-[η]测得了聚碳硅烷（PCS）的分子量、分子量分布和分子的形态与尺寸;通过IR-NMR-元素分析联合,定量表征了组成PCS的结构基团及支化程度。结果表明,常压高温裂解法合成的PCS是一种分子量较低,分子量分布较窄的低聚物,分予内以Si—C键为主的六元稠环组成的扁球体状分子,分子的支化程度很高,分子结构很紧密,等效球体半径（Re）在甲苯中约为1nm左右。     

聚碳硅烷/二乙烯基苯粘度特性研究

通过粘度实验,研究了20～140℃温度范围内浸渍用聚碳硅烷(PCS)/二乙烯基苯(DVB)体系流变学性质。PCS在DVB中以溶解和熔融的方式分散,温度为影响体系粘度的关键因素。结果表明PCS/DVB体系在80～120℃的温度范围内,粘度低于300mPa·s,可满足浸渍要求。     

巯基化合物／乙烯基聚硅氮烷光固化体系的研究

采用三种巯基化合物作为含乙烯基聚硅氮烷(PSN-1)的光固化剂,研究了三种巯基化合物与PSN-1的反应动力学,并对光固化产物进行了热重分析.结果表明:巯基化合物/ PSN-1体系的反应速率与巯基浓度的一次方成正比,与乙烯基浓度无关,均为一级反应;四元巯基化合物比二元巯基化合物的初始反应速率快,而转化率偏低;四巯基季戊烷/PSN-1体系的陶瓷产率高达89%,更适合作先驱体转化法制备陶瓷材料的陶瓷先驱体.     

异氰酸酯改性聚硅氮烷的合成及性能研究

采用甲苯二异氰酸酯( TDI)与聚硅氮烷PSN2反应,制备了异氰酸酯改性聚硅氮烷.用红外、凝胶渗透色谱及热重分析对反应产物进行了表征,比较了反应温度及原料比例对产物的结构、摩尔质量、黏度及热性能的影响.结果表明,在相同反应温度下,随着TDI用量增加,产物的摩尔质量减小,摩尔质量分布变窄,黏度增加;TDI用量相同时,产物...     

陶瓷前驱体聚硅氮烷的应用研究进展(一)

综述了陶瓷前驱体聚硅氮烷在制备陶瓷涂层、陶瓷纤维、纳米材料、磁性陶瓷上的应用研究进展,指出了应用研究前景。     

先驱体聚碳硅烷的合成研究进展

介绍了近年来先驱体聚碳硅烷(PCS)的制备、性能和应用的研究现状和进展。着重介绍了合成先驱体PCS的主要方法：常压循环热裂解法、高压法、常压催化法和常压高温裂解法。比较了这几种合成方法的优缺点：从用PCS制备陶瓷纤维的用途来说，高压法是一种较成熟的方法，所制备的陶瓷SiC纤维的性能也较好，但装置复杂、成本较高、安全性较差；常压高温裂解法合成装置简单、成本较小、安全性也好，但使用该法制得的陶瓷SiC纤维的性能较差。     

Si-C-N陶瓷前驱体聚硅氮烷合成的研究进展

综述了合成Si—C—N陶瓷前驱体聚硅氮烷的主要方法，即氨／Q解氯硅烷法、硅氮烷低聚物交联法、硅氮烷低聚物与氯硅烷反应法及氯硅氯烷和氯硅烷脱氯编聚法，并介绍了用铝、硼、钛、钇等元素对聚硅氮烷进行改性，以提高Si—C—N陶瓷性能的方法。     

液态超支化聚碳硅烷的合成及应用进展

液态超支化聚碳硅烷（LHBPCS）作为一种SiC陶瓷前体,因具有流动性好、可自交联、陶瓷产率高及热解产物接近SiC化学计量比等优点而备受关注。本文在介绍液态超支化聚碳硅烷特点的基础上,重点综述了它的合成方法,包括开环聚合法、Grignard偶合聚合法、Wurtz偶合聚合法、硅氢加成法等,并总结了液态超支化聚碳硅烷在碳化硅基复合材料、碳化硅纤维、碳化硅薄膜等领域的应用,最后指出液态超支化聚碳硅烷今后的研究重点是规模化合成及改性研究等。     

Accelerating the crosslinking process of hyperbranched polycarbosilane by UV irradiation

A liquid hyperbranched polycarbosilane (LHBPCS) with stoichiometric C/Si ratio but without unsaturated groups was synthesized. Different from traditional thermal crosslinking, ultraviolet (UV) irradiation crosslinking was taken. The molecular weight, the consumption of SiH group and ceramic yield of LHBPCS showed an increase trend with increasing the UV irradiation time. After 30 min of UV irradiation, 71.8 wt% ceramic yield was obtained. In addition, extra divinyldimethylsilane was added into LHBPCS. Under UV irradiation, both the SiH group and vinyl group of divinyldimethylsilane were consumed. But the reaction extend of vinyl group was much faster than that of SiH group. Compared with pure LHBPCS, the mixture of LHBPCS and 5 wt% divinyldimethylsilane gave a higher ceramic yield of 79 wt% after 30 min of UV irradiation. By heating the crosslinked LHBPCS to 1000 °C, a near stoichiometric SiC ceramic was got. It exhibited excellent thermal stability at 1400 °C in air.     

用有机硅聚合物制造陶瓷材料

介绍了国内外用有机硅聚合物制造陶瓷纤维及陶瓷基复合材料方面的进展。     

超高分子质量聚碳硅烷的合成与表征

从常压合成得到的中低分子量PCS出发进行热压合成制备超高分子质量的PCS,并对其结构和性能进行了表征。研究表明控制热压反应温度在460~470℃、预加压力1~2 MPa、反应6h时得到先驱体PCS的Mw为6 400~8 500;热压合成后制得的超高分子质量PCS的Si—H含量和支化度有所降低;通过控制热压反应时间可以较好的调控超高分子PCS的重均分子质量的大小。     

Study on crosslinking of polymers and joining mechanism of SiC ceramic

ABSTRACT

Based on crosslinking of polymers with different vinyl contents at low temperature and pyrolysis of the polymer at high temperature, joining temperature and impregnation cycles of an SiC joint were discussed. Polyvinylphenylsiloxane as the polymer with active groups of Si–OH and CH=CH₂ by crosslinking enhances ceramic yield and thermal stability. The microstructure of the polymer changes from amorphous ceramic into grains of SiO₂ and SiC, grains can dispersion strengthening enhances strength of joint layer. Shear strength of SiC joints reaches the maximum at 1200°C. A relatively good interface between the SiC substrate and pyrolysis product of the polymer is formed, but there exist loose cracks or voids in the joint layer which affect the shear strength of the joint. The shear strength of the SiC joint reaches 69.2?MPa through seven times of vacuum impregnation/pyrolysis enhancement. According to the microstructure and properties of the SiC joint, the pyrolysis mechanism of the joining layer as part of the joint by using polyvinylphenylsiloxane is explained.     

Highly effective free-radical-catalyzed curing of hyperbranched polycarbosilane for near stoichiometric SiC ceramics

Liquid hyperbranched polycarbosilane (LHBPCS) is an excellent preceramic polymer of SiC. Before thermolysis, curing of LHBPCS is favorable for higher ceramic yield and molding. In order to avoid some unfavorable factors arising from traditional thermal curing, we introduced a free-radical initiator tert-butyl peroxybenzoate (TBPB) to trigger the crosslinking of allyl group on LHBPCS in this study. FT-IR, NMR and DSC measurements indicated only allyl group was consumed during the cross-linking process. The cross-linking reaction rate was monitored by a rotational rheometer, and results confirmed LHBPCS could be cured in 4 minutes with the help of 1 wt% TBPB at 80°C. TGA and SEM demonstrated the catalytic-cured LHBPCS had a high ceramic yield of 79.0 wt% and dense structure. The effect of TBPB on crystallization behavior of the obtained SiC was also explored by XRD, and little impact was detected. After 1600°C thermolysis, a near stoichiometric and crystalline SiC with ceramic yield of 77.5 wt% was obtained.     

Effect of ultraviolet irradiation on the cross-linking process and ceramic yield of liquid hyperbranched polycarbosilane

Liquid hyperbranched polycarbosilanes (LHBPCSs) with different reactant molar ratios of chloropropene/chloromethyltrichlorosilane were synthesised by Grignard coupling, followed by reduction. Different from traditional thermal cross-linking for LHBPCS, ultraviolet (UV) irradiation cross-linking was used. The molecular weight and hardness of LHBPCS increased with prolonging UV irradiation time. According to Fourier transform infrared result, the –Si–H, –Si–H₂ and allyl groups were consumed. Possible cross-linking reactions (hydrosilylation, allyl group polymerisation and dehydrocoupling) were discussed. The ceramic yield of LHBPCS showed an increase trend with increasing the UV irradiation time. After 1?h of UV irradiation for LHBPCS-1 (the molar ratio of chloropropene to chloromethyltrichlorosilane was 1:9), 78.0?wt-% ceramic yield was obtained. In addition, LHBPCS with higher allyl group content had fewer pores in it. By heating LHBPCS-1 cross-linked by UV irradiation to 1400°C, a non-porous SiC ceramic was obtained.     

Improving the ceramic yield of polycarbosilane by radiation cross‐linking in the presence of multifunctional monomers

An interesting method for radiation cross‐linking polycarbosilane (PCS) at high efficiency and low cost was developed by adding multifunctional monomers (trimethylolpropane trimethacrylate (TMPTMA) or divinylbenzene (DVB)). The effect of multifunctional monomers on the radiation cross‐linking and ceramic yield of PCS was investigated. The results revealed that the addition of a small amount of multifunctional monomer can substantially improve the ceramic yield and reduce the absorbed dose by promoting cross‐linking. The ceramic yields of radiation cross‐linked “PCS/2%DVB (300 kGy)” and “PCS/2%TMPTMA (300 kGy)” were 74 wt% and 78 wt%, respectively, while that of the radiation cross‐linked “PCS (300 kGy)” was only 64 wt%. The presence of double bonds in multifunctional monomers stimulated the combination reactions of free radicals in PCS induced by γ‐ray irradiation and subsequently enhanced the efficiency of cross‐linking. Furthermore, it was found that the incorporation of a small amount of multifunctional monomer hardly affected the chemical composition and crystallization behavior of the final SiC ceramics.