液态29Si NMR研究TEOS/DDS混合体系的氨催化水解动力学

原位引入有机组分对氧化硅体系改性是合成有机-无机杂化硅材料的重要方法.利用原位的29Si液体核磁,研究了甲醇为溶剂、氨水催化条件下的四乙氧基硅烷(TEOS)和二甲基二乙氧基硅烷(DDS)原位共水解的动力学过程.通过改变反应体系中氨和水的浓度,拟合出单体及中间产物浓度随时间的变化曲线,得到了TEOS和DDS各自的水解速率常数以及相应各反应物的反应级数.与单前驱体水解一致的是,在双前驱体系中TEOS和DDS自身的反应级数仍保持一级,但是氨和水的反应级数都有不同程度的增大.与单前驱体水解速率方程相比,混合体系中TEOS的水解速率常数增大.同时,DDS在双前驱体中比单前驱体中的水解速率常数有很大程度的减少.水解动力学表明,TEOS和DDS在双前驱体体系中显示出更平行的水解速率.利用固体29SiMAS NMR,XPS及小角X射线散射(SAXS)手段对双前驱体体系研究得到的信息显示,碱催化条件下原位的TEOS水解中间物与DDS中间产物的原位共缩聚程度很弱.     

29Si NMR研究TEOS/DDS双前驱体体系的水解动力学

原位引入有机组分对氧化硅体系改性是合成有机-无机杂化硅材料的重要方法. 利用原位的²⁹Si液体核磁, 研究了甲醇为溶剂、氨水催化条件下的四乙氧基硅烷(TEOS)和二甲基二乙氧基硅烷(DDS)原位共水解的动力学过程. 通过改变反应体系中氨和水的浓度, 拟合出单体及中间产物浓度随时间的变化曲线, 得到了TEOS和DDS各自的水解速率常数以及相应各反应物的反应级数. 与单前驱体水解一致的是, 在双前驱体系中TEOS和DDS自身的反应级数仍保持一级, 但是氨和水的反应级数都有不同程度的增大. 与单前驱体水解速率方程相比, 混合体系中TEOS的水解速率常数增大. 同时, DDS在双前驱体中比单前驱体中的水解速率常数有很大程度的减少. 水解动力学表明, TEOS和DDS在双前驱体体系中显示出更平行的水解速率. 利用固体²⁹Si MAS NMR, XPS及小角X射线散射(SAXS)手段对双前驱体体系研究得到的信息显示, 碱催化条件下原位的TEOS水解中间物与DDS中间产物的原位共缩聚程度很弱.     

29Si NMR研究St(o)iber反应的化学动力学

Stoiber反应以低分子量的醇为溶剂,由正硅酸乙酯(TEOS)在氨催化下水解缩聚形成高度分散的尺寸为5～2000 nm的球形SiO2颗粒,是溶胶-凝胶过程的典型反应.通过液体29Si NMR研究Stoiber反应水解和缩聚的动力学过程,确定了反应过程的中间体是Q10,而不是文献所说的Q61.得到了TEOS碱性条件下决速步的水解速率方程r=kh[TEOS][NH3]0.457·[H2O]0.051,其速率常数为kh＝7.32×10-3 mol-0.5·dm1.5·min-1 (T=25 ℃),利用过渡态理论得到决速步以外的反应方程的速率常数.同时得到了反应活化能Ea和指前因子A的值.结果表明,温度升高,所有反应的速率均增大,决速步的反应速率增大得较多,说明升高温度更有利于Q10的生成;水量的改变对所有反应速率几乎没有影响;催化剂的用量对其水解和缩聚速率影响较大.     

~(29)SiNMR研究Stber反应的化学动力学

St ber反应以低分子量的醇为溶剂 ,由正硅酸乙酯 (TEOS)在氨催化下水解缩聚形成高度分散的尺寸为 5～ 2 0 0 0nm的球形SiO2 颗粒 ,是溶胶 -凝胶过程的典型反应 .通过液体2 9SiNMR研究St ber反应水解和缩聚的动力学过程 ,确定了反应过程的中间体是Q10 ,而不是文献所说的Q61.得到了TEOS碱性条件下决速步的水解速率方程r =kh[TEOS] [NH3 ] 0 .457·[H2 O] 0 .0 51,其速率常数为kh=7.3 2× 10 -3 mol-0 .5·dm1.5·min-1(T =2 5℃ ) ,利用过渡态理论得到决速步以外的反应方程的速率常数 .同时得到了反应活化能Ea 和指前因子A的值 .结果表明 ,温度升高 ,所有反应的速率均增大 ,决速步的反应速率增大得较多 ,说明升高温度更有利于Q10 的生成 ;水量的改变对所有反应速率几乎没有影响 ;催化剂的用量对其水解和缩聚速率影响较大 .     

简单一级反应数据处理的一个新模型

利用产物和反应物某一物理性质的差别来测定反应速率、确定动力学参数是常用的方法.过氧化氢催化分解、蔗糖水解等典型的物理化学实验都是以物理性质代替浓度进行动力学测定,最后确定反应速率常数的.     

色谱质谱联用技术研究30%二甲基二乙氧基硅烷/70%正硅酸乙酯复合醇盐的水解聚合行为

采用色谱质谱联用技术研究了1种复合醇盐：30％二甲基二乙氧基硅烷／70％正硅酸乙酯（DDS／TEOS）的水解聚合过程，并由此分析了这两种有机-无机酸盐的相互作用机制和聚合方式，实验结果指出，DDS的添加抑制了TEOS的自聚合，使得体系中形成了大量的DDS的自聚合环状分子（（（CH3）2Si—O—）n）以及TEOS和DDS的共聚合高分子，由于后者对水解聚合的加速作用，使得30％DDS／70％TEOS系统具有最短的凝胶时间。     

氨基功能化介孔吸附剂的一步合成及其重金属吸附性能

以聚甲基含氧硅氧烷(PMHS)、正硅酸乙酯(TEOS)和氨丙基三甲氧基硅烷(APTMS)作为反应前驱体,在无需传统结构导向剂的溶胶-凝胶体系中制备了介孔结构发达的氮基功能化凝胶吸附剂,并采用元素分析、固体核磁共振、傅里叶红外光谱、低温氮气吸附/脱附、透射电镜和热重分析等手段对产物结构性能进行了表征.氮气吸附和透射电镜测...     

热致性液晶聚合物的种类对液晶/环氧树脂共混物固化反应动力学的影响

采用等温DSC固化动力学研究方法,用自催化动力学模型对反应型热致性液晶聚合物/环氧树脂共混体系进行研究.结果表明,EP/DDS未改性体系,在α＜40%范围遵循自催化反应机理;EP/DDS/LCPU共混改性体系,在α＜60%范围遵循自催化动力学反应机理,而且自催化反应速率和非催化反应速率均大于未改性体系,表明反应型热致性液晶聚合物的活性基团对固化反应起到了催化促进作用;EP/DDS/PHBHT共混改性体系能够较好符合n级反应机理,固化反应的活化能较大,说明没有反应基团的液晶聚合物(PHBHT)对固化反应无明显促进作用.     

RhCl_3/CH_3I催化醋酸甲酯羰基化制醋酐——Ⅱ.LiOAc存在下的动力学和机理

1.前言 在醋酸甲酯羰基化高活性均相铑催化体系中,CH_3I和锂化合物及含氮、膦有机物是最常用的助催剂。Schrod等首先对RhCl_3—CH_3I—有机碱—络合物体系催化醋酸甲酯羰基化反应动力学及红外光谱进行了研究,发现反应对醋酸甲酯为零级;CO的反应级数在压力1.5MPa以上也为零级;铑和CH_3I反应级数为一级;膦的反应级数随浓度增加由一级变为零级;Cr(CO)_6对反应速率影响不大,同时发现存在着中间反应物Rh(CO)_2I_2~-。根据这些实验事实,他们提出了类似于甲醇羰基化制醋酸的催化反应机理,认为速率控制步骤是CH_3I与Rh(CO)l-2~-的氧化加成,但他们没有报导有关锂化物助催剂的作用。Eastman公司的研究人员Polichnowski研究了RhCl_3—CH_3I—Lil体系催化醋酸甲酯羰基化动力学和原位红外光谱,也发现当反应总压在3.0MPa以上时,反应初速与CO压力无关,但RhCl_3,CH_3I和LiI等浓度     

由硅酸酯合成单分散二氧化硅中碳的化学形态

单分散二氧化硅是指尺寸分布十分狭窄的二氧化硅颗粒．单分散颗粒在科学研究及工业应用中得到了广泛的应用［1］．单分散二氧化硅由正硅酸有机酯在氨催化下于醇溶液中水解缩合得到．硅酸酯的水解和缩合反应可用如下反应描述．总的反应式为：nSi（OR）4＋2nH20→nSiO2＋4nROH1956年Kolbe［2］发现正硅酸乙酯（TEOS）在碱催化下于乙醇溶剂中水解反应有时会形成均一颗粒二氧化硅以来，许多学者对这一反应体系进行了较为广泛的研究，提出了双分子缩合成核机理、单分子叠加生长机理、表面反应控制生长机理、扩散控制生长机理和微晶核团聚生…     

Ammonia Catalyzed Hydrolysis-Condensation Kinetics of Tetraethoxysilane/Dimethyldiethoxysilane Mixtures Studied by <Superscript><Emphasis Type="Bold">29</Emphasis></Superscript>Si NMR and SAXS

In-situ ²⁹Si liquid-state nuclear magnetic resonance (NMR) was used to investigate the ammonia catalyzed hydrolysis and condensation of the mixed systems of tetraethoxysilane (TEOS) and dimethyldiethoxysilane (DDS) dissolved in methanol. With ammonia catalysis, the hydrolysis reaction orders for TEOS and DDS in the mixed systems remained first order, which is similar to that observed for their corresponding single silane component precursor systems. The hydrolysis rate constant for TEOS in the mixed systems was larger than that of TEOS in the single silane component precursor systems. Meanwhile, the hydrolysis rate constants of DDS in the mixed precursor systems were smaller than those of DDS in the single silane component precursor systems. The hydrolysis and condensation kinetics showed more compatible hydrolysis-condensation relative rates between TEOS and DDS, which remarkably affected the final microstructure of the resulting silica particles. Small angle X-ray scattering (SAXS) experiments showed a typical double fractal structure in the particulate networks.     

A new study on the kinetics of Stöber synthesis by in-situ liquid 29Si NMR

Liquid-state ²⁹Si NMR was used to investigate the hydrolysis and condensation kinetics of ammonia-catalyzed tetraethoxysilane (TEOS) in methanol system. The reactive rate constants were calculated by applying first-order reaction approximation and the steady state approximation theory. The reaction orders with respect to TEOS, ammonia and water were derived, as well as the activation energies and the Arrhenius constants. It was found that the formation of intermediate species Si(OH)(OEt)₃ was the rate-limiting step and its reaction rate equation was r _TEOS=7.41×10⁻³[TEOS][NH₃]^0.333[H₂O]^0.227. Higher reactive temperature benefited the hydrolysis of TEOS. The results presented here indicated quantificationally that the formation of colloidal SiO₂ particles was controlled by the initial hydrolysis of TEOS.     

TS-1分子筛的合成Ⅰ.29Si和1H NMR研究正硅酸乙酯的水解

利用29Si和1H NMR方法研究了TS-1分子筛合成过程中正硅酸乙酯(TEOS)的水解行为.1H NMR结果表明,TEOS在四丙基氢氧化铵(TPAOH)溶液中的水解速度快于在四乙基氢氧化铵(TEAOH)中的水解速度.TEOS水解后的29Si NMR谱显示,TEOS在TPAOH中水解产生的聚合硅酸根物种的分布与在TEAOH中的类似,都存在着单体、二聚、三聚及环聚等硅酸根物种的平衡,但TEOS-TEAOH体系中低聚硅酸根物种的浓度明显大于TEOS-TPAOH中的浓度.向水解后的样品中添加水,可促使多聚硅酸根物种转化为低聚物种.大量异丙醇的加入将导致单聚和二聚硅酸根物种的高聚.钛酸四丁酯加入到TEOS-TPAOH水解体系中得到的29Si NMR结果明显不同于TEOS-TEAOH水解体系.     

Size, volume fraction, and nucleation of Stober silica nanoparticles

29Si NMR, small-angle X-ray scattering (SAXS), and dynamic light scattering (DLS) are used to monitor the synthesis of silica nanoparticles from the base-catalyzed hydrolysis of TEOS in methanol and ethanol. The reactions are conducted at a [TEOS] =0.5 M, low concentrations of ammonia ([NH(3)] =0.01-0.1 M), and [H(2)O] =1.1-4.4 M to resolve the initial size of the first nuclei and to follow their structural evolution. It is found that after an induction period where there is a buildup of singly hydrolyzed monomer, the first nuclei are fractal and open in structure. Interestingly, the nuclei are twice as large in ethanol (R(g) approximately 8 nm) as those in methanol (R(g) approximately 4 nm). The data suggest that the difference in primary particle size is possibly caused by a higher supersaturation ratio of the singly hydrolyzed monomer in methanol than in ethanol if it is assumed that the surface energy of the first nuclei is the same in methanol and ethanol. The particle number concentration and the volume fraction of the silica particles are calculated independently from the SAXS, DLS, and 29Si NMR results. Finally, the rate of nucleation is obtained from the particle number concentrations.     

MCM-48介孔分子筛的高压合成

采用正硅酸乙酯（TEOS）作硅源,十六烷基三甲基溴化铵（CTAB）为模板剂,在高压 （约7 MPa）和373 K下合成了MCM-48介孔分子筛.用XRD、氮气吸附及29Si MAS NMR对样品 进行了表征.与常压合成的相比,高压下合成的MCM-48具有更高的热稳定性和水热稳定性.2 9Si MAS NMR结果表明,高压有利于分子筛孔壁的聚合,导致分子筛结构更加完善,从而使 其具有更高的稳定性.     

Fluorescence probing investigation of the mechanism of formation of MSU-type mesoporous silica prepared in fluoride medium

The mechanism of formation of a MSU-type siliceous material from tetraethyl orthosilicate (TEOS) in the presence of the nonionic surfactant tergitol T-15-S-12, sulfuric acid, and sodium fluoride has been investigated using mainly fluorescence probing techniques and, to a lesser extent, dynamic light scattering (DLS) and 29Si NMR spectroscopy. The tergitol micelles present in the systems obtained by progressively generating the reaction mixture giving rise to the mesostructured material by adding to an appropriate tergitol solution sulfuric acid, TEOS, and NaF were characterized by fluorescence probing (micelle aggregation number, micropolarity, and microviscosity) and also by dynamic light scattering (apparent micelle diameter). 29Si NMR experiments were also performed on selected systems after hydrolysis of the TEOS. The fluorescence probing techniques were also used to follow the changes of micelle characteristics with time during the evolution of the full reaction mixture from a limpid solution to a system containing a minor amount of condensed siliceous material. The synthesized solid material was characterized by X-ray diffraction and nitrogen adsorption-desorption analyses. The micelle aggregation number N was found to change only little, and the micropolarity remained constant when going from the tergitol solution to the full reaction mixture. The results of DLS measurements agree with this finding. Besides, while the condensation of silica took place after addition of NaF, the N value increased only very little with time up to the point where a small amount of mesostructured material precipitated out. These results indicate that the interaction between tergitol micelles and the siliceous species formed in the system by the hydrolysis of TEOS and also between micelles and the growing siliceous species must be very weak. As in our previous studies of the mechanism of formation of MCM41-type material from sodium silicate in the presence of cetyltrimethylammonium bromide, it appears that the locus of formation of the mesostructured material is not the micelle surface but the bulk phase. Micelles only act as reservoirs of surfactant providing surfactant monomer that binds to the growing siliceous species.     

光固化聚氨酯丙烯酸酯杂化材料的核磁共振谱

光固化聚氨酯丙烯酸酯杂化材料的核磁共振谱;SiO2;溶胶-凝胶法     

Interfacial water with special electron donor properties: effect of water-surfactant interaction in confined reversed micellar environments and its influence on the coordination chemistry of a copper complex

The long-time behavior of the hydrolysis and condensation reaction of the tetraethoxysilane (TEOS) pre-solution at different pH values with and without addition of polyethyleneglycol (PEG) for various aging times was characterized by liquid (1)H, (13)C, and (29)Si NMR spectroscopy. After aging, the alcohol is released in the TEOS pre-solution without addition of PEG at pH 3 and 9. On the other hand, the hydrolysis and condensation rates of the TEOS pre-solutions with addition of PEG at pH 3 and 9 increase except for the TEOS pre-solution with addition of PEG 2000 at pH 9. However, the hydrolysis and condensation rates of the TEOS pre-solutions with and without addition of PEG at pH 5 and 7 are almost the same before and after aging. The effects of the pH values, polymer size and aging times on the hydrolysis and condensation reaction of the TEOS pre-solutions are discussed.     

Coating of Tetraethylorthosilicate (TEOS)/Vinyltriethoxysilane (VTES) Hybrid Solution on Polymer Films

Tetraethylorthosilicate (TEOS)/vinyltriethoxysilane (VTES) hybrid materials were prepared and the hydrolysis and condensation reactions during processing were investigated by means of 29Si NMR solution spectroscopy. The variation of drying characteristics of the coating films was examined with respect to the tetraethylorthosilicate (TEOS)/vinyltriethoxysilane (VTES) ratio, as well as drying temperature, by FT-IR spectroscopy. It is shown that the TO mode of Si–O–Si stretching absorption was enhanced with increasing tetraethylorthosilicate (TEOS) content and drying temperature. Also, the wettability of the coating films on polymer films was independent of the solution composition but enhanced by the precoating of poly(4-hydroxystrene) (PHS) as a wetting agent. The adhesion between the coating and the films was also enhanced when the vinyltriethoxysilane (VTES) content in the coating solution was increased.