通过在线~7Li-NMR谱对负离子聚合见解的进一步验证

通过对正丁基锂(n-BuLi)/四氢呋喃(THF)引发α-甲基苯乙烯(mSt)负离子本体聚合,验证了n-BuLi缔合体可以引发聚合,形成超分子团聚体,然后在进一步聚合过程中超分子解离.证实了先前提出的负离子聚合的引发机理.通过7Li-NMR对聚合过程的在线检测,进一步证实了mSt在氘代苯为溶剂,THF为调节剂下的负离子聚合以及异戊二烯在非极性条件下的溶液聚合都存在引发剂多元缔合体向二元缔合体转变.研究还发现,少量THF可能使n-BuLi的六元缔合结构2～3个进一步串联起来,但先于六元缔合结构解离.此外,THF与n-BuLi作用,随着n-BuLi/THF的摩尔比从1∶1到1∶5的变化,可以使n-BuLi的巨大缔合体解离并向六元缔合体转变.     

二茂铁-四氰基乙烯络合体的光化学反应

在基态,由弱的电荷转移所形成的缔合体,一般称之为"电荷转移络合体",这种络合体的液相光化学反应,早已引起有机化学家的极大兴趣,并已进行了广泛的研究。     

苯乙烯阴离子本体聚合引发剂缔合及其机理的研究

分别以正丁基锂和叔丁基锂为引发剂,采用自制管式流动反应装置,对较高温度下苯乙烯阴离子本体聚合动力学进行了研究.证实了正丁基锂主要以六元缔合结构形式引发聚合,并导致超分子团聚体的形成,从而使进一步的聚合因单体扩散受阻而受到限制,并伴随聚合转化率停滞平台（SCP）的产生.随后由于前期聚合累积的能量,使超分子结构完全解离.聚合温度越高,SCP持续时间越短.结果还表明,在正丁基锂引发剂中,存在一个以六元缔合结构为基础形成的更大的缔合体结构.原子力显微镜照片显示,超分子结构的直径分别为20～30nm和50～60nm.此外,在阴离子聚合过程中活性种的缔合结构只决定于初始引发剂的分子结构,而不同活性种缔合结构对阴离子聚合的链增长存在很大影响,从而解释了采用不同结构的锂系引发剂引发苯乙烯单体聚合时聚合速率存在巨大差异的原因.     

配位聚合及高分子催化剂金属络合物的结构与反应活性

东京大学平井英史在国际上首先直接测定出配位聚合中金属络合物的浓度和结构,进而探明了反应机理,并将极性高分子与金属盐配位,获得了活性和选择性都很高的加氢催化剂。平井发现,配位聚合得到的均聚物,其立构规正度因络合物的种类而异,是其结构的本征反映。金属盐(如SnCl_4,ZnCl_2)-极性乙烯基单体-给电子单体形成的三组份分子络合体,则在低温下或添加自由基聚合引发剂时,能得到高分子量的1:1的交替     

钒(V)硫脲氧化还原体系引发丙烯腈聚合的研究——Ⅲ.钒(V)在聚合过程中的作用

研究了钒(V)—硫脲氧化还原体系引发丙烯腈聚合反应中五价钒对链引发和链终止所起的作用。从钒(V)—硫脲体系浓度对聚合物产率关系,发现在引发体系的“临界浓度”区内,聚合速度发生跳跃式的变化。这一事实进一步证明导致链自由基的产生和终止的作用物的基本结构可能同是络合体(V~(5+)-2TU)。。并且讨论了由本工作所得的钒(V)的反应级数和文献报告的结果出现分岐的主要原因。     

稀土催化辛烯—1齐聚物的合成

采用膦酸钕-三乙基铝络合体系在四氯化碳溶剂中聚合辛烯-1获得成功,并描述了体系的聚合反应特征。所得辛烯-1齐聚物M_n～10~3,分子量分布指数≈2,并且分子链中含有双键。采用高锰酸钾在酸性溶液中的直接氧化法将分子键中的双键氧化成羧基,并与聚乙二醇发生酯缩聚反应。     

配位体对铑催化低压羰基合成的影响(Ⅱ)——几种有机磷和亚磷酸酯配位体的比较

本文分别以三(对甲基苯基)膦,亚磷酸三(对甲基苯基)酯,亚磷酸三(对氯苯基)酯,亚磷酸三(邻甲氧基苯基)酯,亚磷酸三苯基酯等为配位体,以二羰基乙酰丙酮铑为催化剂母体,研究1—庚烯醛化反应的动力学和反应产物的分布,用动力学结果和测得的催化剂体系的红外光谱羰基伸缩振动频率与文献[1]结果比较,进一步说明烯醛化反应的速率不仅决定于其反应的控制步骤,而且与反应体系中活化络合体的浓度有关.亚磷酸三(3,4-二甲基苯基)酯有利于活化络合体的形成,其作为配位体时,醛化反应的速率较其它配位体高得多,同时由于其较大的立体化学效应,提高了对产物中直链醛的选择性.     

α-甲基苯乙烯阴离子平衡聚合热力学研究

本文研究了α-甲基苯乙烯聚合热力学。发现平衡单体浓度不仅与聚合温度有关,而且依赖于引发剂浓度。本文还报导了缔合体和单量体引发β-甲基苯乙烯聚合的平衡常数、聚合热、浆合熵及聚合自由焓。     

原位交联杂化型聚合物电解质膜的形成机理、结构模型及其电化学性能

合成含有Ti(Ⅵ)杂化中心的交联(柠檬酸钛络合体-聚乙二醇)聚酯网络作为基体,水解生成的Nano-TiO₂粒子为填料,LiI/I₂为导电离子,通过原位聚合复合法制备了Nano-TiO₂/(柠檬酸钛络合体-聚乙二醇)/LiI/I₂交联杂化型聚合物电解质膜。采用局域密度近似(LDA)法、Raman光谱、傅里叶变换红外光谱(FTIR)、透射电子显微镜(TEM)和能量散射X射线分析(EDXA)探讨了交联杂化聚合物基体的形成机理,并建立了其相应的结构模型。在此基础之上,研究了四异丙氧基钛(Ti(iOPr)₄)的含量对Nano-TiO₂/(柠檬酸钛络合体-聚乙二醇)/LiI/I₂电解质膜的结构及电化学性能的影响。研究表明:当Ti(iOPr)₄含量高于12 % (w)时,Nano-TiO₂粒子和Ti(Ⅵ)杂化中心的共同作用不仅有效提高了电解质膜的离子电导率(σ),而且显著改善了电解质膜与电极间的界面稳定性;Ti(iOPr)₄含量为48 % (w)时,电解质膜的室温离子电导率达到最大值9.72×10^-5 S·cm^-1,电解质膜的界面电阻于6d后趋于稳定。     

甲基丙烯酸甲酯在褐藻酸钴(Ⅱ)络合物膜、亚硫酸钠和水介质中的自由基聚合

本文研究了一种新颖的自由基聚合体系-褐藻酸钴(Ⅱ)络合物膜和亚硫酸钠在水介质中引发的甲基丙烯酸甲酯的聚合反应。考察了反应条件对MMA转化率的影响。实验表明。褐藻酸钴(Ⅱ)络合物膜可以多次重复使用而不失去其活性。紫外-可见光谱表明,体系中存在着含有聚合物基体的活性大络合体。提出了引发机理,自由基是通过络合态的HSO_3~-向络合态的单体进行的氢转移而产生的。     

Polymerizability of norbornene in ring-opening metathesis polymerization initiated by Mo-based complexes

Concerning the study on the relation between structural parameters and reactivity in ring-opening metathesis polymerization of cyclo-olefins, the “living” polymerization of norbornene initiated by Schrock's-type complexes was considered as a reference and studied from the kinetic point of view. First kinetic orders with respect to both monomer and active species allow the values of absolute rate constants of propagation to be determined. The thermodynamic parameters obtained from kinetic experiments performed at different temperatures seem to indicate that monomer coordination and metallacycle formation are rate-determining steps in the process studied. © 1994 John Wiley & Sons, Inc.     

Kinetic modeling studies of ethylene polymerization reactions using supported chromium catalysts

Kinetic models for ethylene polymerization based on a general coordination–insertion mechanism, in which either a monocoordinated species or a bicoordinated species could lead to migratory insertion, were constructed. These models were implemented through the solution of a set of differential equations resulting from the material balances for all the species involved. The application of these kinetic models to monomer consumption for different supported catalysts produced very good fittings and allowed the estimation of the kinetic rate constants of each elementary step. Although the same kinetic scheme was used to describe all the observations, the results of the fitting showed that the supported chromium species behaved very differently according to the support. Only in the case of the silica‐supported catalysts was mechanical fragmentation of the particles observed during the course of the reaction, and this implied the inclusion of a new term in the model. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3464–3472, 2004     

Study of ε-caprolactone polymerization by NIR spectroscopy

Near-infrared (NIR) spectroscopy is proposed for the in-line quantitative and kinetic study of the polymerization of ε-caprolactone and eventually to facilitate real-time control of the manufacturing process. Spectra were acquired with a fibre-optic probe operating in transflectance mode immersed in the reactor. The NIR data acquired were processed using a multivariate curve resolution alternating least squares (MCR-ALS) algorithm. The proposed method allows calculation of the concentration and spectral profiles of the species involved in the reaction. The key point of this method is the lack of reference concentrations needed to perform the MCR-ALS method. The use of an extended spectral matrix using both process and pure analyte spectra solves the rank deficiency. The concentration profiles obtained were used to calculate a kinetic fitting of the reaction, but the method was improved by applying kinetic constraints (hard modelling). The rate constants of batches at different temperatures and the energy of activation for this reaction were calculated. Whenever possible, the hard modelling combined with the MCR-ALS method improves the fit of the experimental data: the results show good correlation between the NIR and reference data and allow the collection of high-quality kinetic information on the reaction (rate constants and energy of activation).     

Modeling stable free-radical polymerization

A kinetic model has been developed for stable free-radical polymerization (SFRP) processes by using the method of moments. This model predicts monomer conversion, number-average molecular weight, and polydispersity of molecular weight distribution. The effects of the concentrations of initiator, stable radical, and monomer, as well as the rate constants of initiation, propagation, termination, transfer, and the equilibrium constant between active and dormant species, are systematically investigated by using this model. It is shown that the ideal living-radical polymerization having a linear relationship between number-average molecular weight and conversion and a polydispersity close to unity is the result of fast initiation, slow propagation, absence of radical termination, and a high level of dormant species. Increasing stable radical concentration helps to reduce polydispersity but also decreases polymerization rate. Thermal initiation significantly broadens molecular weight distribution. Without the formation of dormant species, the model predicts a conventional free-radical polymerization. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2692–2704, 1999     

The persistent radical effect in controlled radical polymerizations

We describe the basic kinetic features of “living” polymerizations controlled and regulated by persistent radicals or related species and by reversible atom transfer. In these systems a special kinetic phenomenon operates—the Persistent Radical Effect. It is also known from selective organic syntheses and reflects a self-inhibition of the termination reaction. Analytical equations for the polymerization rates and for the polydispersities of the resulting polymers are presented, and important requirements for reaction rate constants leading to control are outlined. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1885–1901, 1999     

An ESR Approach to the Estimation of the Rate Constants of the Addition and Fragmentation Processes Involved in the RAFT Polymerization of Styrene

The reversible‐addition‐fragmentation chain transfer (RAFT) controlled radical polymerization of such vinylic monomers as styrene (= ethenylbenzene) has gained increasing popularity in current years. While there is a general agreement on the mechanism of RAFT polymerization, there is an ongoing debate about the values of the rate constants of its key steps, i.e., the addition of the propagating radicals to the mediator and the fragmentation of the resulting spin adducts. By carrying out an ESR spectroscopic investigation of the AIBN‐initiated polymerization of styrene (AIBN = 2,2′‐azobis[2‐methylpropanenitrile]), mediated by benzyl (diethoxyphosphoryl)dithioformate ( 5 ) as RAFT agent, we were able to detect and characterize four different radical species involved in the process. By reproducing their concentration–time profiles through a kinetic model, the addition and fragmentation rate constants at 90° of the propagating radicals to and from the mediator were estimated to be ca.10⁷ M ^?1 s^?1 and ca. 10³ s^?1, respectively. The validity of the kinetic model was supported by hybrid meta DFT calculations with the BB1K functional that predicted addition‐ and fragmentation‐rate‐constant values in good agreement with those estimated from the ESR experiments.     

Kinetic scheme and rate constants for methyl methacrylate synthesis occurring via the radical–coordination mechanism

Two kinetic schemes of the bulk radical–coordination polymerization of methyl methacrylate initiated by the benzoyl peroxide–ferrocene system are considered from the standpoint of formal kinetics. The most likely kinetic scheme is the one that includes the reactions characteristic of classical radical polymerization and, additionally, reactions of controlled radical polymerization proceeding via the Organometallic Mediated Radical Polymerization mechanism, a reaction generating a coordination active site, and a chain propagation reaction in the coordination sphere of the metal. The temperature dependences of the rate constants for the reactions of this kinetic scheme at temperatures typical of commercial poly(methyl methacrylate) production (313–353 K) have been determined by solving the inverse kinetic problem.     

过氧化氢的热分解及其引发丙烯腈聚合反应的研究

本文研究了过氧化氢在二甲基甲酰胺中的热分解反应,测定了不同温度下的分解速率常数和表现活化能。同时研究了过氧化氢引发丙烯腈的聚合反应,确定了聚合动力学方程。     

Polymerization of acrylonitrile initiated by the redox system 2,2′-thiodiethanol/Ce4+ in aqueous sulfuric acid

The polymerization of acrylonitrile initiated by the redox system 2,2′-thiodiethanol/Ce⁴⁺ in dilute sulfuric acid was investigated in the temperature range of 15–25°C. Oxidation of the substrate in the absence of the monomer has also been studied. The reaction involves the formation of an intermediate complex between the metal ion and the protonated species of the reductant, whose decomposition gives rise to the initiating free radicals. Multual interaction of the growing macroradicals accounts for the termination of polymerization. A suitable kinetic scheme has been proposed and rate and equilibrium constants evaluated.     

Kinetic heterogeneity of the active sites of titanium-containing catalytic systems in the stereospecific polymerization of isoprene

The kinetic heterogeneity of the active sites of titanium-containing catalytic systems in the stereospecific polymerization of isoprene was studied based on solving inverse problems for the molecular-weight distribution of polyisoprene with the use of the Tikhonov regularization method. It was found that from two to four types of active sites can occur depending on the nature of the organoaluminum compound used in the catalytic system. The rate constants of elementary steps of the polymerization process for particular types of active sites were obtained for the first time by solving inverse kinetic problems.