On the Scaling Study for the A_f-A_g Type Free Radical Polymerization

根据Ａｆ－Ａｇ自由基加聚反应的数量分布函数，导出凝胶点附近的渐进分布函数和高分子矩的表示式．进一步应用标度变换，得到了描述溶胶－凝胶相变的广义标度律，从而揭示了Ａｆ－Ａｇ自由基加聚的固化反应是一个相变过程．     

高分子电解质溶胶—凝胶相转移与溶剂效应

以溶质、溶剂间的协同作用作为高分子电解质体系的凝胶化条件，以松软粒子结构（Ｂｏｌｂ）间的三维逾渗的凝胶化模型，将高分子电解质体系的凝胶化分为松软粒子的形成和逾渗过程。结合海藻酸溶液的Ｃｕ＾２＋、Ｃａ＾２＋、Ｍｎ＾２＋和Ｃｏ＾２＋离子添加体系的凝胶化，分析了高分子电解质溶胶－凝胶相转移的实质，得到了体系相对粘度的临界指数ｋ＝－０．９０￣１．１４，与逾渗模型的预测值相吻合，探讨了松粒子的形成对相转移介     

高分子电解质溶胶－凝胶相转移与溶剂效应

以溶质、溶剂间的协同作用作为高分子电解质体系的凝胶化条件，以松软粒子结构（Ｂｌｏｂ）间的三维逾渗的凝胶化模型，将高分子电解质体系的凝胶化分为松软粒子的形成和逾渗过程。结合海藻酸溶液的Ｃｕ２＋、Ｃａ２＋、Ｍｎ２＋和Ｃｏ２＋离子添加体系的凝胶化，分析了高分子电解质溶胶－凝胶相转移的实质，得到了体系相对粘度的临界指数ｋ＝０．９０～１．１４，与逾渗模型的预测值相吻合，探讨了松软粒子的形成对相转移临界点ｆｃ的影响，明确了临界点附近相对粘度的幂次公式ηｒｅｌ∝（ｆｃ—ｆ）－ｋ）的适用范围。     

聚(N-异丙基丙烯酰胺)水溶液物理交联网络的形成过程

对ＰＮＩＰＡＭ／水体系的动态黏弹谱分析发现,在相变温度（约３２℃）以下该体系为均相的黏弹性流体．升温至３２℃左右溶液发生相变,贮存模量Ｇ’突然急剧增大,超过了损耗模量Ｇ”,表明体系形成了物理交联的网络结构．以逾渗模型为基础,分别利用动态标度理论和Ｗｉｎｔｅｒ判据决定了该体系的凝胶化温度Ｔ_（ｇｅｌ）,通过动态标度理论还得到了临界标度指数ｎ＝０．７９,与由逾渗模型预测的化学交联网络的标度指数值０．６７不同,这反映了物理交联网络的特殊性．     

自由基引发的凝胶化反应的Monte Carlo模拟

基于自由基凝胶化反应的基本原理,在一个具有周期性边界条件的二维网络上,利用动态ＭｏｎｔｅＣａｒｌｏ 方法模拟了聚合物凝胶的自由基凝胶化反应,得到了凝胶的具体结构,研究了总单体浓度（ 单体浓度和交联剂浓度之和） 对凝胶的分形结构和孔径分布的影响．模拟中首次考虑了聚合后单体的运动对凝胶结构的影响．结果表明：考虑聚合后单体的运动,可使所得凝胶网络的分形维数和凝胶化所需的最低浓度均显著小于动力学凝胶化模型和ＤＬＡ 模型的相应值．用移动气泡法得到了凝胶网络的孔径分布,发现凝胶网络中大孔所占百分率明显多于随机纤维网络模型．     

溶剂效应与海藻酸钠溶液溶胶-凝胶相转移

以溶质、溶剂间的协同作用作为高分子电解质体系的凝胶化条件，以松软粒子结构（Blob）间的三维修滤过程作为体系的凝胶化模型，从而将高分子电解质体系的凝胶化分为松软粒子的形成和渗滤过程．结合不同浓度海藻酸钠溶液的Ca2＋离子深加体系的凝胶化，分析了高分子电解质溶胶-凝胶相转移的实质，得到了体系相对粘度的临界指数k＝0．90～0．97和相转移的临界点fc与聚合物浓度间的幂次关系fc～c-0.65，明确了临界点附近相对粘度的幂次公式ηrel∝（fc-f）-k的适用范围．     

光散射技术在研究高分子溶液和凝胶方面的应用

从溶液中的高分子、凝胶粒子及微乳胶粒子形态结构的表征和凝胶化过程、微乳液聚合及大分子缔合等动态过程的跟踪等方面的研究综述了近十几年来光散射技术在高分子溶液和凝胶领域的应用,并简单介绍了光散射技术的基本原理、发展简史和仪器及使用方法。     

阳离子诱导海藻酸水溶液凝胶化的临界行为与自相似性

以作者对阳离子诱导海藻酸水溶液凝胶化的研究结果为中心,介绍了海藻酸钠水溶液随浓度增大和二价金属阳离子(Ca2 、Cu2 )的加入而发生的溶液-凝胶转变的临界点和相关临界指数,探讨了临界凝胶的自相似性和分形结构,以及动态标度理论对物理交联体系的适用性.基于对阳离子诱导海藻酸水溶液凝胶化及其临界行为的研究结果,提出了从凝胶化的出发点--溶液来对凝胶化进行分类的设想,根据起始组分分子链的长短将凝胶化过程分为生长型和交联型两类.     

非线性Af—Bg型自由基交替共聚反应的固化理论

利用高分子反应统计理论,给出了非线性Ａｆ－Ｂｇ型自由基交替共聚反应的溶胶－凝胶分配方程和反应体系的凝凝胶化条件,这些结果是进一步研究与凝胶网络性能相关的网络结构参数的基础。     

多组分高分子体系动态流变学研究

根据动态流变学基本理论介绍了多组分高分子体系动态流变学行为,评述了动态流变学方法在研究高分子共混体系、嵌段共聚物体系、填充高分子体系及溶胶-凝胶体系的形态、结构方面的最新进展,认为动态流变学方法是研究多组分高分子体系形态与结构的一种有效方法.     

3,4-二-O-乙酰基-L-阿拉伯烯糖与HR—CH2—CH=CH2（R=O,CH2,NH,S）的Ferrier重排反应机理

采用密度泛函理论方法对3,4-二-O-乙酰基-L-阿拉伯烯糖与HR—CH2—CH=CH2(R=O,CH2,NH,S)反应的Ferrier重排反应机理进行了研究,并通过自洽场极化连续模型(PCM)模拟了苯和二氯化碳溶剂对反应历程的影响,计算了相应结构的单点能,考虑了2条可能的反应途径,获得了较优反应途径和反应速率控制步骤.研究表明:苯和二氯化碳溶剂的溶剂效应未对反应历程产生明显影响.R基电负性越大、体积越大以及H+的存在,均有利于该重排反应进行.     

L-缬氨酸旋光异构的两种光反应可能途径

利用密度泛函理论(DFT)和从头算分子轨道理论对L-缬氨酸的旋光异构光反应机理进行了研究. 分别用B3LYP和MP2方法在6-311++G(d, p)基组级别上全优化得到了S₀和T₁态反应路径上的反应物、产物、中间体以及过渡态结构的几何构型, 给出了反应能垒, 利用含时密度泛函理论(TD-DFT)中的B3LYP/6-311++G(d, p)方法优化得到了S₁态反应路径上的平衡态几何构型. 通过分析反应途径上各个驻点的几何构型特征, 确定了L-缬氨酸在激发态可能通过手性碳上的氢原子以羰基氧或氨基氮为中转媒介发生质子迁移来完成旋光异构反应. 进一步用自洽反应场理论中的极化连续模型(PCM)方法探讨了溶剂化效应对旋光异构反应机理的影响.     

聚甲基丙烯酸甲酯热氧化降解的化学动力学研究

使用质谱、热分析手段研究了PMMA热解反应.结果表明,在氮气中,PMMA-CH=CH2有两个失重阶段,分别对应于主链末端双键引发的断链和主链无规则断链反应,转折点的失重率约为26%.其中,第一阶段的失重速率受扩散过程控制,平均表观活化能E为158.5 kJ/mol, lnA为27.69;第二失重阶段为1.5级化学反应,平均表观活化能E为214.79 kJ/mol, lnA为40.46.在空气中, PMMA也有两个失重阶段,反应机理为1级化学反应,转折点处的失重率约为70%.其中在第一失重阶段平均表观活化能E为130.32 kJ/mol, lnA为24.81,在此阶段中, 过氧化基团的分解反应对PMMA的失重速率有重要影响; 在空气中第二失重阶段平均表观活化能E为 78.25 kJ/mol, lnA为13.97.     

Addition reaction of adamantylideneadamantane with Br2 and 2Br2: a computational study

Ab initio calculations were carried out for the reaction of adamantylideneadamantane (Ad=Ad) with Br2 and 2Br2. Geometries of the reactants, transition states, intermediates, and products were optimized at HF and B3LYP levels of theory using the 6-31G(d) basis set. Energies were also obtained using single point calculations at the MP2/6-31G(d)//HF/6-31G(d), MP2/6-31G(d)//B3LYP/6-31G(d), and B3LYP/6-31+G(d)//B3LYP/6-31G(d) levels of theory. Intrinsic reaction coordinate (IRC) calculations were performed to characterize the transition states on the potential energy surface. Only one pathway was found for the reaction of Ad=Ad with one Br2 producing a bromonium/bromide ion pair. Three mechanisms for the reaction of Ad=Ad with 2Br2 were found, leading to three different structural forms of the bromonium/Br3- ion pair. Activation energies, free energies, and enthalpies of activation along with the relative stability of products for each reaction pathway were calculated. The reaction of Ad=Ad with 2Br2 was strongly favored over the reaction with only one Br2. According to B3LYP/6-31G(d) and single point calculations at MP2, the most stable bromonium/Br3- ion pair would form spontaneously. The most stable of the three bromonium/Br3- ion pairs has a structure very similar to the observed X-ray structure. Free energies of activation and relative stabilities of reactants and products in CCl4 and CH2ClCH2Cl were also calculated with PCM using the united atom (UA0) cavity model and, in general, results similar to the gas phase were obtained. An optimized structure for the trans-1,2-dibromo product was also found at all levels of theory both in gas phase and in solution, but no transition state leading to the trans-1,2-dibromo product was obtained.     

Reaction mechanism of monoethanolamine with CO₂ in aqueous solution from molecular modeling

We present a theoretical study of the reaction mechanism of monoethanolamine (MEA) with CO? in an aqueous solution. We have used molecular orbital reaction pathway calculations to compute reaction free energy landscapes for the reaction steps involved in the formation of carbamic acids and carbamates. We have used the conductor-like polarizable continuum model to calculate reactant, product, and transition state geometries and vibrational frequencies within density functional theory (DFT). We have also computed single point energies for all stationary structures using a coupled cluster approach with singles, doubles, and perturbational triple excitations using the DFT geometries. Our calculations indicate that a two-step reaction mechanism that proceeds via a zwitterion intermediate to form carbamate is the most favorable reaction channel. The first step, leading to formation of the zwitterion, is found to be rate-determining, and the activation free energies are 12.0 (10.2) and 11.3 (9.6) kcal/mol using Pauling (Bondi) radii within the CPCM model at the CCSD(T)/6-311++G(d,p) and CCSD(T)/6-311++G(2df,2p) levels of theory, respectively, using geometries and vibrational frequencies obtained at the B3LYP/6-311++G(d,p) level of theory. These results are in reasonable agreement with the experimental value of about 12 kcal/mol. The second step is an acid-base reaction between a zwitterion and MEA. We have developed a microkinetic model to estimate the effective reaction order at intermediate concentrations. Our model predicts an equilibrium concentration for the zwitterion on the order of 10?11 mol/L, which explains why the existence of the zwitterion intermediate has never been detected experimentally. The effective reaction order from our model is close to unity, also in agreement with experiments. Complementary ab initio QM/MM molecular dynamics simulations with umbrella sampling have been carried out to determine the free energy profiles of zwitterion formation and proton transfer in solution; the results confirm that the formation of the zwitterion is rate-determining.     

Computational study of the aminolysis of anhydrides: effect of the catalysis to the reaction of succinic anhydride with methylamine in gas phase and nonpolar solution

Different possible pathways of the aminolysis reaction of succinic anhydride were investigated by applying high level electronic structure theory, examining the general base catalysis by amine and the general acid catalysis by acetic acid, and studying the effect of solvent. The density functional theory at the B3LYP/6-31G(d) and B3LYP/6-311++G(d,p) levels was employed to investigate the reaction pathways for the aminolysis reaction between succinic anhydride and methylamine. The single point ab initio calculations were based on the second-order M?ller-Plesset perturbation theory (MP2) with 6-31G(d) and 6-311++G(d,p) basis sets and CCSD(T)/6-31G(d) level calculations for geometries optimized at the B3LYP/6-311++G(d,p) level of theory. A detailed analysis of the atomic movements during the process of concerted aminolysis was further obtained by intrinsic reaction coordinate calculations. Solvent effects were assessed by the polarized continuum model method. The results show that the concerted mechanism of noncatalyzed aminolysis has distinctly lower activation energy compared with the addition/elimination stepwise mechanism. In the case of the process catalyzed by a second methylamine molecule, asynchronous proton transfer takes place, while the transition vectors of the acid-catalyzed transition states correspond to the simultaneous motion of protons. The most favorable pathway of the reaction was found through the bifunctional acid catalyzed stepwise mechanism that involves formation of eight-membered rings in the transition state structures. The difference between the activation barriers for the two mechanisms averages 2 kcal/mol at various levels of theory.     

气相中Y^＋活化CS2中的C—S键

以Y+与CS2反应作为第二行前过渡金属离子与CS2反应的范例体系.采用密度泛函UB3LYP方法,对于Y+采用Stuttgart赝势基组,对于CS2采用6-311+G(2d)基组,计算研究了Y+离子在基态和激发态时与CS2气相反应的机理.并用UCCSD(T)方法在相同的基组水平上对各驻点作了单点能量校正.结果表明Y+离子与CS2的反应是插入-消去反应,在反应过程中会发生系间窜越,并且找到了两个势能面的能量最低交义点.     

Au(111)面上肉桂醛的选择性加氢机理

采用密度泛函理论并结合周期性平板模型的方法,优化了肉桂醛在Au(111)面上的吸附模型,并详细探讨了肉桂醛在Au(111)面上选择性加氢的反应机理(C=O,C=C以及1,4共轭加成机理).计算结果表明,肉桂醛以C=O和C=C协同吸附于Au(111)面上时,吸附构型最稳定.此时,不同吸附模式的吸附能平均在140.0kJ?mol-1.通过搜索不同机理下每个基元反应的过渡态,得出肉桂醛在Au(111)面上最可能的选择性加氢产物为苯丙醛,且其按照1,4共轭加成机理间接得到苯丙醛比C=C直接加氢机理具有更低的活化能.具体反应过程为:肉桂醛C=O的O优先加H形成烯丙基型中间体,继而该中间体中与苯环相连的C原子继续加H形成烯醇(ENOL),最终烯醇异构成苯丙醛.其中ENOL的生成过程所需的活化能最高,是反应的控速步骤.     

凝胶点前氯乙烯－邻苯二甲酸二烯丙基酯共聚物表征，支化度模型及悬挂双键活性

根据单烯－二烯自由基共聚合反应特点，提出一种新的支化点对分子量的分布模型，讨论了用凝胶色谱－特性粘数法表征文化聚合物时，文化点对分子量分布和式［η］０，ｂ／［η］０．１＝ｇ０中的指数ｃ对结果的影响．建立了氯乙烯－二烯类单体悬浮聚合凝胶点前的平均支化度模型．用凝胶点前平均文化度和平均分子量模型拟合实验结果发现：ａ．新的支化分布模型更合理，且ｃ＝０．７２；ｂ．悬挂双键活性下降一个数量级；ｃ．对本文样品，特性粘数和分了量仍符合Ｍａｒｋ－Ｈｏｕｗｉｎｋ方程，［η］＝０．２３５７Ｍ￣０．５２７．     

Si(001)-(2×2×1):H表面O2吸附的密度泛函理论研究

A novel model was developed to theoretically evaluate the O2 adsorption on H-terminated Si(001)-(2*2*1) surface. The periodic boundary condition, the ultrasoft pseudopotentials technique based on density functional theory (DFT) with generalized gradient approximation (GGA) functional were applied in our ab initio calculations. By analyzing bonding energy on site, the favourable adsorption site was determined. The calculations also predicted that the adsorption products should be Si=O and H2O. This theoretical study supported the reaction mechanism provided by Kovalev et al. The results were also a base for further investigation of some more complex systems such as the oxidation on porous silicon surface.