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1.
《Ceramics International》2022,48(3):3311-3327
A liquid carbon-rich SiAlCN precursor is facilely synthetized by hydrosilylation between liquid polyaluminocarbosilane (LPACS) and 1,3,5,7-tetravinyl- 1,3,5,7-tetramethylcyclotetrasilazane {[CH3(CH2CH2)SiNH]4} (TeVSZ). The structural evolution during the polymer-ceramic conversion process is investigated by various methods. The results show that the main cured mechanism is β-addition on hydrosilylation, although α-addition on hydrosilylation, polymerization of vinyl groups and dehydrocoupling reaction between N–H bonds also occur during the cured process. During the pyrolysis process, dehydrogenation and dehydrocarbonation condensation reactions, transamination reactions occur, leading to formation of a three-dimensional network inorganic structure at 400–800 °C, where part of Al–O bonds convert to Al–N bonds. Then the network inorganic structure undergoes demixing and separation into amorphous SiAlCN(O) phase, where the amorphous turbostratic free carbon phase also form at 800–1200 °C. With demixing and decomposition of the amorphous carbon-rich SiAlCN(O) phase, the crystalline β-SiC and graphitic carbon start to form at about 1400 °C, the crystalline sizes of them both enlarge with increasing temperature. However, the crystal growth of β-SiC is distinctly inhibited due to existence of the rich carbon phase, tiny amounts of Al2O3 and AlN. In addition, a small amount of AlN can promote the formation of α-SiC at 1800 °C.  相似文献   
2.
Polycarbonsilane (PCS) is an important precursor of silicon carbide (SiC) fibers and ceramics. The ceramic yield of PCS is relatively low, about 60 %, which may bring some deficiencies in its applications. In this work, a novel precursor cyano-polycarbosilane (PCSCN) is synthesized by hydrosilylation reaction between PCS and acrylonitrile using a rhodium-containing catalyst, although acrylonitrile is generally not easy for hydrosilylation. After introducing tiny amounts of cyano (-C≡N) groups into the PCS molecules, the ceramic yield of PCSCN can increase largely to over 80 %. The ceramization mechanism of PCSCN is investigated by FTIR, TG, XPS, ESR, NMR, Raman and XRD analyses. It is found that some crosslinking structures in PCSCN are formed between SiH bonds and CN groups from about 200 ℃, which can be responsible for the high ceramic yield. The existence of a little more N, O and free C elements in the pyrolysis products may inhibit the growth of crystalline β-SiC. Moreover, the PCSCN precursor can also be melt-spun into continuous fibers by tailoring its molecular weight and softening point. The oxidized PCSCN fiber with relatively low oxygen content can be pyrolyzed without melting, and the final SiC fiber with an oxygen content as low as 8.5 % is obtained.  相似文献   
3.
An effective synthesis of polysiloxanes containing mixed functional groups was carried out using consecutive hydrosilylation of two different olefins. With the functionalization of polysiloxanes, we sought to obtain derivatives containing fluoroalkyl groups (with hydrophobic properties) and reactive groups capable of attaching a polysiloxane to the surface. Glycidyl and trimethoxysilyl groups were chosen for the study. All of the obtained derivatives were isolated and spectroscopically characterized. In the next stage of the study, glass plates were modified with functionalized polysiloxanes, both alone and with added silica sol, and their hydrophobic properties were determined by measuring contact angles. From the results, we determined the effect of functionalized polysiloxane structure on the hydrophobic properties of polysiloxane-modified surfaces.  相似文献   
4.
The surface of spherical nonporous monodisperse silica particles (diameter: 200 nm) is covalently modified with hydride by means of hydrosilanization. A direct silicon-carbon link between the hydride modified silica surface and 10-undecylenic acid is obtained by photochemical radical initiated hydrosilylation. A ferrocene unit is attached through an amide link to the carboxylic acid modified surface. Solid-state NMR and DRIFT spectroscopy indicate success of the reactions. The electrochemical oxidation and reduction of the ferrocene modified silica particles are observed after their adsorption on a platinum electrode. The cyclic voltammograms indicate, in addition to the charge transfer between ferrocene units on the particle surface, an interparticle charge transfer.  相似文献   
5.
The Command-Cure concept is defined for a curable formulation as one with long work-like at ambient temperature and rapid cure time at elevated temperature. This concept is explored for a curable silicone system, cured via hydrosilylation. CODMCl2 complexes (COD=1.5-cyclo-octadiene:M=Pt. Pd) are reacted with beta-cyclodextrin (-CD) to make 11 inclusion compounds,M=Pd.2;M=Pt.4. Compounds2 and4 were analyzed by1H NMR and X-ray powder diffraction. Their catalytic ability was evaluated in a model system as well as a polymeric system that gels upon cure. Surprisingly, the Pd analog2 was a good command-cure catalyst whereas the guest compound CODPdCl2,1, was not active in the hydrosilylation reaction. The Pt analog,4, was an effective command-cure catalyst while the corresponding guest. CODPtCl2,3, was too active at low temperature in the hydrosilylation reaction. Additional Pt compounds and one Rh inclusion compound were evaluated as command cure catalysts. These inclusion compounds were: 11 -CD:[CODRhCl]2,5: 11 -CD:CpPtMe3,6 (Cp=cyclopentadienyl): 12 -CD:MeCpPtMe3,7; 12 -CO:CODPtMe2,8. The effectiveness of4 8 was evaluated in a number of silicone systems.  相似文献   
6.
The preparation, properties, catalytic kinetics and use as a hydrosilylation catalyst of a silica-supported Karstedt (Pt)-type catalyst are reported. This type of catalyst has high catalytic activity at room temperature under an atmospheric pressure, and the catalyst can be reused five times without any appreciable loss in the catalytic activity.  相似文献   
7.
Sylvie Boileau 《Polymer》2003,44(21):6449-6455
Telechelic, hydroxyalkyl terminated polydimethylsiloxanes were obtained under mild conditions via hydrosilylation of allyl alcohol or ethylene glycol monoallyl ether by oligomeric αω-hydride terminated polydimethylsiloxanes, with the use of a platinum catalyst. They were subsequently modified in a phase transfer catalyzed reaction by propargyl bromide, to give telechelic polysiloxanes terminated by acetylenic groups. The synthetic pathway is described and the characterization of the obtained products is presented.  相似文献   
8.
Treatment of a dihydrosilane (methylphenylsilane, 1) with mixtures of a diyne (p- or m-diethynylbenzene, 2a or 2b) and a triyne (1,3,5-triethynylbenzene, 3a or B,B′,B″-triethynyl-N,N′,N″-trimethylborazine, 3b; 1:2:3=100:95:5, 100:90:10, 100:80:20) in the presence of Pd-PCy3 (Cy=cyclohexyl) catalyst gave new crosslinked silylenedivinylene polycarbosilanes. In TGA the resulting crosslinked polymers tended to show higher Td5 values and higher char yields than the corresponding linear polymers. On the other hand, UV/vis absorption spectra of the crosslinked polymers obtained in the reactions of 2a or 2b with 3a exhibited increased broad peaks around 390 nm for 2a or 360 nm for 2b. Coincidently, their fluorescence spectra showed significant increase of the emission peaks in 400-550 nm. The crosslinked polymer derived from 2a and 3b, however, showed decrease of the absorption peak around 390 nm and profound depression of fluorescence peaks in 400-550 nm.  相似文献   
9.
以八甲基环四硅氧烷(D4)、四甲基环四硅氧烷(D4^H)和六甲基硅氧烷(MM)为原料实施开环聚合反应,制备出不同含氢量的聚二甲基硅氧烷;含氢硅氧烷与乙酸乙烯酯进行硅氢加成反应,在硅氧烷大分子侧链上引入酯基;然后碱性条件下进行醇解反应,最后成功合成了不同羟烃基含量的聚硅氧烷。对产物的结构、乳化稳定性、乳液粒径及成膜的表面性能等进行了研究。结果表明,该方法可调控聚硅氧烷的羟烃基含量,改善聚硅氧烷亲水性能。当D4^H用量达到10%时,可获取粒径较小的水分散液,其亲水疏水平衡值(HLB)可达13,乳液稳定时间长达126 h。涂膜后与水的接触角可降低至70.7°。  相似文献   
10.
Iron N-heterocyclic carbene research has witnessed a spectacular growth in the last decade. A wide number of catalytic applications have been recently disclosed, demonstrating the enormous potential of Fe-NHCs in organic synthesis. Catalytic reductions of multiple bonds through hydrogenation, transfer hydrogenation, hydrosilylation and hydroboration processes constitute important transformations. To date, this field of research is still in its infancy. Over the past few years our group has contributed to this area by developing new efficient and selective iron-NHC complexes for the reduction of unsaturated organic groups. This review provides a concise overview of Fe-NHC catalysed reduction reactions to push for further progress in this exciting area of research.  相似文献   
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