共查询到18条相似文献,搜索用时 125 毫秒
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硅氮烷添加剂的水解稳定性对硅橡胶热稳定性的影响 总被引:6,自引:0,他引:6
采用一种新的方法研究了硅氮烷水解反应的动力学规律 ,根据实验数据测出硅氮烷水解速率对硅氮烷的浓度符合一级动力学关系 .计算出了几种硅氮化合物与水蒸气反应的表观活化能 ,结果表明硅氮烷的结构与其水解反应的表观活化能有密切的关系 .硅原子或氮原子上带有较大空间位阻的基团后 ,其水解稳定性提高 .其中六苯基环三硅氮烷 4的水解表观活化能为 2 14kJ mol,而苯基硅氮聚合物 5的水解表观活化能更达到 2 91 3kJ mol.添加到硅橡胶中的硅氮化合物水解表观活化能越大 ,即水解稳定性越高 ,其改进硅橡胶热稳定性的效果越好 .将 4和 5添加到硅橡胶生胶中 ,35 0℃下老化 2 4h的热失重分别为 0 96 %和 0 6 % . 相似文献
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硅氮化合物的结构与水解稳定性的关系 总被引:1,自引:0,他引:1
采用硅氮化合物本体与水蒸汽直接作用的方法,研究了一系列硅氮化合物的结构与水解稳定性之间的关系.结果表明,空间位阻越大则硅氮化合物水解稳定性越好,环张力对硅氮烷的水解稳定性有一定的影响,但空间位阻的作用更为显著.带有苯基的环二硅氮烷、六苯基环三硅氮烷和含硅氮键的高分子聚合物具有较大的空间位阻,因此水解稳定性非常好. 相似文献
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讨论了不同结构的硅氮烷与羟基硅油的本体反应,研究了反应动力学,结果表明该本体反应为二级反应,其反应活化能约为44KJ/mol:硅氮烷中的氮含量愈高、N/Si比愈大、结构中环张力的存在等都使反应速度加快、硅原子上引入苯基取代基会使反应速度减慢。同时也讨论了温度对反应速度的影响。 相似文献
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氢气作为全球公认的清洁能源载体,备受关注。寻找安全高效的储氢材料以转型到氢能社会是当前氢能应用面临最大的挑战之一。氨硼烷(NH3BH3,AB)具有非常高的储氢质量分数(19.6 wt%)和体积储氢密度(0.145 kgH2/L),因其在储氢和放氢性能方面的显著优势,被认为是一种颇具应用潜力的化学储氢材料。氨硼烷能够通过热解、醇解和水解放出氢气。其中,氨硼烷水解制氢可以通过催化剂进行可控放氢,且具有反应条件温和、不产生CO(易使催化剂中毒)等优点,被认为是一种安全高效和实用性强的制氢技术。本文简要介绍了氨硼烷的性质和合成,阐述了氨硼烷水解制氢的机理,综述了近年来氨硼烷水解制氢催化剂的研究进展,分析了碱对氨硼烷水解制氢的促进作用,并讨论了水解产物回收利用问题。 相似文献
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William Clegg Uwe Klingebiel George M. Sheldrick Dietmar Stalke 《Journal of organometallic chemistry》1984,265(1):17-25
The thermal elimination of LiF from lithium aminofluorosilanes provides a simple synthetic route to four-membered silicon-nitrogen rings. In attempts to inhibit sterically the otherwise ready dimerisation of such lithium salts, t-butyl, mesityl and silylamine substituents were introduced. The lithiation of the fluorotris(silylamino)silane (Me3SiNMe)2SiF-NHSiMe2CMe3 and the thermal elimination of LiF led to the formation of a cyclodisilazane, involving migration of a methanide and a silylmethylamine in one of the monomer precursors. The crystal structure of this product has been determined from 3375 unique diffractometer-measured intensities, and refined to R = 0.070. The space group is P21/n, with a 12.458(2), b 22.589(3), c 16.376(4) Å, β 102.33(1)° and Z = 4. 相似文献
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《结构化学》1984,(2)
<正> M =667.0, monoclinic, P21/n, a=11.854(2), b=10.136(1), c=29.931(4) A, β=93.51(1)°, Z=4, V=3588.9(8)A3, Dx=1.23 Mgm-3, λ(MoKα)=0.71069A, μ(Mo-Kα)=2.0, F(000)=1408, room temperature, R=0.072 for 3015 reflections. The structure was solved by direct method.The cyclodisilazane ring is a flattened tetrahedron. The three bonds on N(1) and N(2), respectively, are in a plane. The mean bond lengths of Si-C (methyl), Si-C(phenyl), Si-O, Si-N(endocyclic) and Si-N(exo-) are 1.839, 1.847, 1.636, 1.744 and 1.711A, respectively. 相似文献
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氨化大孔球状聚氯乙烯固定化木瓜蛋白酶的研究 总被引:9,自引:0,他引:9
以氨化大孔球状聚氯乙烯为载体,采用戊二醛载体交联的方法,将木瓜蛋白酶进行了固定化。以酪蛋白为底物,测定了固定化酶的活力回收。研究了固定化条件对固定化酶活力回收的影响。同时,对所得固定化酶的性质,如温度-活力关系、pH-活力关系、热稳定性以及重复使用性进行了考察。结果表明,所得固定化木瓜蛋白酶具有较好的稳定性和重复使用性。 相似文献
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Timoshkin A. Yu. Sevast'yanova T. N. Davydova E. I. Suvorov A. V. Schaefer H. F. 《Russian Journal of General Chemistry》2002,72(12):1911-1915
Structural and thermodynamic characteristics of the trans-SiH4·2NH3 adduct were obtained by ab initio and DFT (RHF and B3LYP) calculations. Scanning the potential energy surface (PES) of the com plex showed that its structure corresponds to a local minimum, whereas the global minimum corresponds to the free fragments. The energy of the silicon-nitrogen chemical bond was calculated with inclusion of fragment rearrangement energies and basis set superposition error. The procedure offered for calculating the Si-N bond energy was extended to adducts of silicon halides with ammonia. It was found that the energy of SiX4 rearrangement contributes most to the energies of donor-acceptor bonds in mono- and diammoniates of silicon tetrahalides. 相似文献
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Gabor Erdodi Jungmee Kang Joseph P. Kennedy 《Journal of polymer science. Part A, Polymer chemistry》2010,48(11):2361-2371
We describe the design, synthesis, characterization, and testing of novel polyurethanes (PUs) exhibiting unprecedented combinations of outstanding mechanical properties and oxidative/hydrolytic stabilities. This achievement is due to the use of polyisobutylene (PIB) soft segments plus flexible H‐bond acceptor chain extenders (HACEs): the PIB imparts superior oxidative/hydrolytic stability and the HACE produces reinforcing H‐bonds, which lead to outstanding mechanicals. Oxidative/hydrolytic stability was quantitated by retention of tensile strength and elongation after exposure to nitric acid. PUs containing 60–70% PIB retain their mechanical properties, whereas Carbothane®, Bionate®, and Elast‐Eon?, PUs marketed for chemical stability, degrade severely under the same conditions. Various HACEs were identified (e.g., hexaethylene glycol, tripropylene glycol, tributylene glycol, 3,3′‐diamino‐N‐methyl‐dipropylamine, etc.) and their effect on mechanical properties was investigated. A PIB‐ and HACE‐containing PU exhibited 29.2 MPa tensile strength, 620% elongation, and 80 Shore A hardness. Properties were analyzed in terms of stress–strain profiles, differential scanning calorimetry traces, dynamic mechanical thermal analysis plots, and oxidative/hydrolytic stability. The properties of various PIB‐based rubbers, that is, thermoplastic PUs, SIBSTAR®, and thermoset butyl rubber are compared. The novel PUs are promising candidates for biomaterials and industrial applications where a combination of mechanical properties and oxidative/hydrolytic stability is of the essence. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2361–2371, 2010 相似文献
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Summary The hydrolytic stability of the ester bond of O-aminoacyl derivatives of N-acetylglucosamine, glucosamine (base), and methyl N-acetylneuraminate has been studied at pH 1–8. It has been shown that the stability of the O-aminoacyl derivatives of N-acetylglucosamine is comparable with that of the corresponding glucose derivatives. The presence of a free amino group in glucosamine leads to a considerable labilization of the ester bond. The ester bond of the O-aminoacyl derivatives of methyl N-acetylneuraminate is characterized by a very high lability, and this must be taken into account in working with biopolymers.Khimiya Prirodnykh Soedinenii, Vol. 4, No. 1, pp. 28–32, 1968 相似文献
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The effect of base sequence on the stability of the transition state (TS) of phosphodiester bond cleavage within linear single-stranded oligoribonucleotides has been studied in order to better understand why the reactivity of some phosphodiester bonds is enhanced compared to an unconstrained linkage. Molecular dynamics simulations of 3.0 ns were carried out for 14 oligonucleotides that contain in the place of the scissile phosphodiester bond a phosphorane structure mimicking the TS of the bond cleavage. The hydrolytic stability of the same oligonucleotides had previously been reported. Both the non-bridging oxyanions and the leaving 5[prime or minute]-oxygen of the pentacoordinated phosphorane moiety were observed to form hydrogen bonds with solvent water molecules in a similar way with all the compounds studied. In addition, water mediated hydrogen bonds between the phosphorane non-bridging oxyanions and the bases of the 3[prime or minute]-flanking sequence were detected with some of the compounds, but not with the most labile ones. Hence, it seems that the enhanced cleavage of some internucleosidic linkages does not result from the TS stabilisation by hydrogen bonding. With heterooligomers, the stacking of bases next to the cleavage site was observed to be enhanced on going from the initial state to the TS, whereas within uracil homooligomer, having initially negligible stacking, no change in the magnitude of stacking was seen. Accordingly, while strong stacking in the initial state is known to retard the phosphodiester bond cleavage, it may in the TS accelerate the reaction. Therefore, enhanced stacking on going from the initial state to transition state appears to be a factor that markedly contributes to the hydrolytic stability of phosphodiester bonds within oligonucleotides and may, at least partly, explain accelerated cleavage compared to fully unconstrained bonds, such as those in polyuridylic acid. 相似文献