具有优异纺丝性的陶瓷先驱体含铝聚碳硅烷的合成及表征

选择适当分子量的低分子量聚碳硅烷与Al(AcAc)3在自制常压高温合成装置中合成了含铝碳化硅纤维的先驱体--聚铝碳硅烷(polyaluminocarbosilane,PACS).并对PACS进行了软化点测试、傅立叶红外光谱(FT-IR)分析、凝胶渗透色谱(GPC)测试、元素分析以及可纺性研究.由中等分子量聚碳硅烷为原料合成出的软化点为194.8～220.1,Si-H键含量为0.857,数均分子量为2353,分子量分布呈"双峰"分布的PACS,经熔融纺丝得到了直径为5μm、表面光滑、直径均匀的原丝,表现出了优异的纺丝性能.     

聚碳硅烷的合成与特性研究

研究了由聚二甲基硅烷热解制备聚碳硅烷的过程，探讨了合成条件笃产物特性的影响。提高反应温度、产物的分子量与熔点随之增高，但同时分子量的分散性增大使可纺性劣化。采用适当的制备方法已获得了具有所需特性的聚碳硅烷。     

以四烯丙基(二甲基)硅烷为核的超支化聚硅碳烷的合成与表征

以四烯丙基(二甲基)硅烷(B4)为核、甲基氢二烯丙基硅烷(AB2)为单体,通过硅氢加成反应,采用无核一步法、核一步法、核多步法合成了超支化聚有机硅碳烷。用FT-IR1、H-NMR、MALLS-GPC对该聚合物的结构进行了表征。研究了核多步法对超支化聚合物分子量及其分布的控制,结果表明,用核多步法合成超支化聚有机硅碳烷可有效地控制产物的分子量及其分布。     

反应温度对液态聚硅烷高压合成聚碳硅烷性能的影响

以液态聚硅烷(LPS)为原料,在高压釜内反应制备了聚碳硅烷(PCS)先驱体。研究发现,随着反应温度的升高．PCS的分子量增大,产率提高,软化点提高．Si—H键含量降低．在反应过程中LPS首先转化为小分子量的PCS．然后是小分子的PCS间发生脱氢及少量脱甲烷缩合使分子量长大。450℃后,反应产率明显增加,分子量分布出现中分子量峰。     

原子转移自由基聚合制备ABA型嵌段共聚物

以α，α’－二溴代二甲苯为引发剂，CuBr/2,2‘－联吡啶为催化体系，制备了双溴端基的分子量分布窄的聚苯乙烯（MWD＝1．21）。再以此作为大分子引发剂，实现了甲基丙烯酸甲酯的原子转移自由基聚合，制得了分子量可控且分子量分布窄的ABA型嵌段共聚物，即聚甲基丙烯酸甲酯－b－聚苯乙烯－b－聚甲基丙烯酸甲酯。     

高分子量聚碳硅烷的合成及其表征

以常压合成的低分子量聚碳硅烷(PCS)为原料,分别在470℃高压及常压下反应一定时间,制备了高分子量PCS先驱体。研究了反应时间对：PCS分子量及其分布、软化点、Si—H键含量及可纺性的影响。研究表明,随着反应时间的延长,PCS低分子量部分逐渐减少,高分子量部分逐渐增加,分子量分布逐渐变宽,从而PCS分子量逐渐增大,软化点逐渐升高,Si—H键含量逐渐降低,可纺性逐渐变差。在相同的反应时间下,高压比常压对PCS分子量的增长更有利。在470℃高压或常压下反应时间2～3h时,可获得分子量高、可纺性良好的PCS先驱体。     

聚碳硅烷的普适标定及Mark-Houwink常数的确定

通过沉淀分级和凝胶色谱(GPC)分级制备了窄分布的聚碳硅烷(PCS),并用多角度激光光散射(MALLS)和GPC分别测定其绝对分子量和分子量分布。采用试差拟合的方法定制了PCS的标定曲线,并用该标定曲线和普适标定方程,确定了25℃时,PCS在四氢呋喃(THF)中的Mark-Houwink常数(K=6.8×10-4mL/g,α=0.855)。经验证,PCS与聚苯乙烯(PS)在THF中符合普适标定关系。     

SiC(Al)陶瓷纤维先驱体聚铝碳硅烷的合成与表征

利用聚二甲基硅烷(PDMS)热解聚合的液相产物聚硅碳硅烷(PSCS)与乙酰丙酮铝(Al(AcAc)3)反应制备了SiC(Al)陶瓷纤维的先驱体聚铝碳譬烷(PACS)，选用PSCS为原料消除了Al(AcAc)3在合成反应过程中出现的升华现象。合成的PACS化学式为：SiC2.0，H2.6Al0.018。数均分子量Mn=2265。研究反应过程发现PSCS发生裂解重排反应，Si-H键在反应中显示出巨大的活性，反应时伴随有乙酰丙酮气相副产物产生。反应机理研究表明，PACS分子量的增加是PSCS形成的Si-H键与Al(AcAc)3的配位基发生交联反应形成Si～Al键的结果。     

添加填料合成SiC（Al）纤维的先驱体聚铝碳硅烷

以聚硅碳硅烷和乙酰丙酮铝为原料,在反应装置的裂解柱中加入填料,在常压下合成了聚铝碳硅烷.结果表明:添加填料使合成聚铝碳硅烷的时间缩短46%,聚铝碳硅烷的从1008增大到2436,分子量的分布变窄,—Si—Si—键的含量低;在N_2气氛中,在400℃以下失重减少,在1200℃陶瓷的产率从65%提高到69%;加入填料可促进—Si—Si—链转化为—Si—C—Si—链,制备出的聚铝碳硅烷纤维在预氧化过程中氧的增重少,预氧化烧成后得到的Si—Al—C—O连续纤维强度为2.1 GPa,在Ar中1800℃烧结可得到致密的SiC(Al)纤维.纤维的结晶行为与不加填料时的类似.     

窄分子量分布的α-乙烯基聚(氟)硅氧烷的合成和表征

合成窄分子量分布的α-乙烯基聚(氟)硅氧烷是制备结构可控的侧链为有机(氟)硅氧烷两亲性梳形聚合物的关键。文中以丁基锂为引发剂,进行了D3和F3的活性阴离子开环聚合。通过实验发现在0℃条件下,用两步聚合法,封端时间11.00 h为较优的开环聚合条件。在此条件下制备了不同聚合度的、窄分子量分布的α-乙烯基聚二甲基硅氧烷和α-乙烯基聚[甲基(3′,3′,3′-三氟丙基)]硅氧烷,聚合物分子量分布在1.15以下。     

Synthesis of continuous silicon carbide fibre with high tensile strength and high Young's modulus

Polycarbosilane as the precursor of continuous SiC fibre was synthesized by thermal decomposition of polydimethylsilane. The structure of the polycarbosilane is concluded to be similar to that of polysilapropylene by the measurements of i.r. spectra, NMR spectra and chemical analyses. Its formation mechanisms are initially the formation of carbosilane by thermal decomposition of polydimethylsilane and then the increase in molecular weight by dehydrogenation-condensation of the carbosilane. Molecular structure and molecular weight distribution of the polycarbosilane depend on the reaction temperature.     

Synthesis of continuous silicon carbide fibre

The polycarbosilane (PC-470) synthesized by thermal decomposition of polydimethylsilane was melt-spun. The conversion process of the fibre into silicon carbide fibre was investigated by chemical analysis, TG-DTA and infra-red spectrum analysis, and measurements of the mechanical properties and densities. The conversion process of polycarbosilane (PC-TMS) synthesized by Fritz was examined and compared with the conversion process of PC-470. It is shown that the process is divided into three stages; condensation at the first stage, thermal decomposition at the second stage and crystallization at the third stage. The mechanical properties and density of the SiC fibre obtained by heattreatment were affected by the molecular weight and structure of the polycarbosilane of the starting material.     

Production mechanism of polytitanocarbosilane and its conversion of the polymer into inorganic materials

The reaction of polycarbosilane with tetra-alkyltitanate proceeded at 300° C in nitrogen atmosphere by the condensation of Si-H bonds in polycarbosilane and the substituent groups of the tetra-alkyltitanate accompanied by evolution of alkan gas, and then the formation of Si-O-Ti bonds occurred. In this condensation reaction using tetra-isopropyl titanate, tetra-n-butyl titanate and tetra-2-ethylhexyl titanate, activation energies of the initial rate of the increase in molecular weight were 17.04, 20.07 and 31.07 kcal mol^–1 respectively, and thus the more bulky the substituent group of tetra-alkyltitanate, the lower the reactivity became. Of these alkyltitanates, tetra-2-ethylhexyl titanate was found to be the most advantageous reactant for obtaining polytitanocarbosilane with a narrow molecular weight distribution, low gel fraction and high titanium concentration. Polytitanocarbosilane with high titanium concentration was converted into the densified amorphous inorganic material with high Si-C bonding energy in high yield. Titanium contained in the pyrolysed polytitanocarbosilane was furthermore found to have the effect of inhibiting crystalline grain growth of -type SiC up to high temperature.     

Synthesis of continuous silicon carbide fibre

Polycarbosilanes which were synthesized by three methods were melt-spun and cured by heating at low temperatures in air. The curing mechanism and the structure of these cured fibres were studied and the relationship between the structure and the pyrolysis process is discussed. The structure of the cured fibre is represented by means of five structural elements and the rate of oxidation of the methyl group. The pyrolysis process of the cured fibre is discussed in five stages, and the effect of oxygen introduced into polycarbosilane fibre by curing on the pyrolysis process is clarified. The structure of the fibre obtained during the pyrolysis process strongly depends on the molecular weight of polycarbosilane.     

Production mechanism of polyzirconocarbo- silane using zirconium(IV)acetylacetonate and its conversion of the polymer into inorganic materials

The reaction of polycarbosilane with zirconium(IV)acetylacetonate proceeded at 573 K in nitrogen atmosphere by the condensation reaction of the Si–H bonds in polycarbosilane and the ligands of zirconium(IV)acetylacetonate accompanied by the evolution of acetylacetone, and then the molecular weight increased by the cross-linking reaction with a formation of Si–Zr bond. The obtained polyzirconocarbosilane showed higher ceramic yield than the polycarbosilane. Zirconium contained in the pyrolysed polyzirconocarbosilane was furthermore found to have the effect of inhibiting crystalline grain growth of -type SiC up to high temperature, so Si–Zr–C–O fibre, which was obtained by the use of polyzirconocarbosilane as precursor, showed high tensile strength up to high temperature.     

低分子量聚碳硅烷制备3D-Cf/SiC复合材料

研究了低分子量聚碳硅烷 (PCS) 通过先驱体浸渍裂解 (PIP) 工艺制备C_f/SiC复合材料。分析表明:PCS的数均分子量为400,活性较强,陶瓷化产率为70％左右,在1200℃基本转化为微晶态的β-SiC。分别通过3种不同升温速率制备了3D-C_f/SiC复合材料试样,其弯曲强度分别为745.2MPa、686.7MPa和762.5MPa,明显高于文献报道3D-C_f/SiC复合材料弯曲强度300~500MPa的水平。试样断口的SEM照片均显示长的纤维拔出,有良好的增韧效果,低分子量PCS裂解得到的基体比较致密。实验结果说明,低分子量PCS适合于制备3D-C_f/SiC复合材料,并且提高升温裂解速率对材料性能影响很小。      

Synthesis of continuous silicon carbide fibre

The structure of polycarbosilane is represented by three structural elements, but their quantification is difficult. Polycarbosilanes were synthesized by three methods and the respective molecular structures were examined by measurements of the molecular weight and the intrinsic viscosity, infrared, ultraviolet,¹H-,¹³C- and²⁹Si-NMR spectral measurements, and chemical analysis. The three structural elements (SiC₄, SiC₃H, SiC _x Si_4–x ) in the polycarbosilane molecule were determined quantitatively. By the comparison between¹H-NMR spectral data and calculation assuming a linear chain structure, the number of linkages in the unit consisting of ten silicon atoms was estimated to be 3 to 4. This result is in agreement with the result from the intrinsic viscosity; it was found that the shape of the polycarbosilane molecule is planar.     

聚碳硅烷熔体的稳态流变性能

采用自制装置对聚碳硅烷(PCS)熔体进行预处理。通过预处理获得三种不同分子量的PCS,并对其进行物理化学和稳态流变性能测试。结果表明,预处理后的PCS其数均分子量为1000 g/mol~1400 g/mol,属低聚物。在温度范围240℃~260℃和剪切速率范围0.001 s-1~10 s-1内有明显的剪切变稀现象。在测试的温度范围内,剪切变稀区的非牛顿指数随温度升高先减小后增大。预处理后的PCS粘流活化能为120 kJ/mol~180 kJ/mol,比一般高聚物的高得多。     

溶剂浸提法调节聚碳硅烷分子量及其分布的研究

真空热处理法去除聚碳硅烷(poIycarbosi-lane,PCS)小分子时,因伴随着化学反应导致PCS结构变化而降低其纺丝性能.溶剂浸提法则无此之虞.研究结果表明,不同溶剂对PCS的溶解能力是不同的,依次为:甲醇<二甲基甲酰胺<乙二醇单甲醚<无水乙醇<乙二醇单乙醚<异丙醇<甲酸乙酯<乙酸甲酯<正丙醇.这一溶解能力体现为可溶PCS量的不同和可溶PCS分子量的不同两个方面.溶解能力较大的溶剂可以溶解分子量较大的PCS;溶解量也较多.由于溶剂的这一特性,溶剂浸提法不仅可以用来去除小分子的PCS,而且可以用来调节PCS的分子量及其分布,改善其纺丝性能,提高其原丝强度,而不改变PCS的分子结构.