AB_g型超支化聚合反应中的环化效应

研究了ABg型超支化聚合反应中的环化效应,给出高分子代数生长的微分动力学方程,并通过环化反应的内在特征确定了环化反应与分子间反应的速率常数.进而利用Monte Carlo模拟方法得到了树状高分子和含环高分子的数量、环的尺寸分布以及高分子数均和重均分子量等,讨论了环化效应对聚合体系平均特征的影响.结果表明,环化效应取决于单体体积分数、溶剂效应和官能度之间的协同作用,其中单体的体积分数在环化反应中起着主导作用,而溶剂效应和官能度之间则相互竞争.     

三元非等活性自缩合乙烯基聚合体系的Z均回转半径

利用Monte Carlo模拟方法研究了由单体、引发单体和引发核组成的三元自缩合乙烯基聚合反应体系. 重点考察了两类活性基团反应活性的差异、引发单体分数、引发核的配比及活性基团数等因素对体系中无核和有核两类超支化高分子Z均回转半径的影响. 结果表明, 这些因素对超支化高分子的结构和尺度影响显著, 因而通过调节有关参数可以实现对超支化高分子结构和尺度的调控.     

典型超支化高分子体系的统计热力学及其应用

以典型的超支化聚合反应体系为例概述了体系的热力学和统计力学性质,重点集中在平均分子量、均方回转半径及支化点密度等特征与热力学量间的关联,以期阐明超支化高分子空间结构与物理性质的调控机制.从空间关联的角度赋予重均聚合度以相应的物理解释,建立其与等温压缩系数的直接关系.通过子链分布导出均方回转半径和流体力学半径的解析形式,并利用高分子的邻接矩阵进行具体计算.在此基础上,从相变与临界现象的角度出发,解释了体系中相关物理量的标度行为,给出相应的广义标度律.为了优化超支化高分子的工业生产流程,引入生成函数方法系统地探讨了分批投料过程中的相关参数对平均高分子量的影响.此外,提出了基于生长代数的Monte Carlo模拟方案,用以辅助研究高分子结构与特征的对应关系.作为应用,揭示了环化效应、溶剂效应及非等活性等因素对聚合反应的影响.     

单官能团单体C存在下A_2-B_2型缩聚产物的分子量分布

分别以概率统计方法和Monte Carlo模拟获得了单官能团单体C存在下A_2-B_2型线型缩聚产物的分子量分布。Monte Carlo方法与统计计算得出一致的结果,表明建立的Monte Carlo模型是合理的。研究了单官能团单体C的反应活性对缩聚产物分子量分布的影响,对反应体系中存在的各种不同的分子类型的消长情况分别进行了动态模拟。     

非等活性加核自缩合乙烯基聚合体系回转半径的Monte Carlo模拟

利用Monte Carlo模拟方法研究了加核自缩合乙烯基聚合反应体系中超支化高分子的二次回转半径随双键转化率的变化情况. 在模拟中, 重点考察了两类活性基团的反应活性差异、 引发核的配比及基团数等因素对超支化高分子均方回转半径的影响. 结果表明, 上述因素对于超支化高分子的尺度有着显著影响, 从而可为调控体系中高分子的空间尺度提供有效途径.     

Thorpe-Ingold效应及其在有机成环反应中的应用

本文首先介绍了Thorpe-Ingold效应及其相关理论和实验研究进展,然后综述了近年来Thorpe-Ingold效应在形成三、四、五和六元环产物的环化反应中的应用。Thorpe-Ingold效应可以有效地促进分子内和分子间环化,提高环化的产率和速率。该效应主要通过空间效应、电子效应或者两者协同起作用,在某些情况下,该效应还会受催化剂和溶剂等影响。利用该效应可以促使一些难以发生的环化反应顺利进行,并能获得较好的产率。     

二元自缩合乙烯基聚合反应体系的统计热力学

应用统计力学原理对二元自缩合乙烯基聚合反应体系(由单体和引发单体组成)的统计热力学特征予以研究.首先从两种不同的角度给出与聚合反应相应的配分函数,据此得到反应体系的平衡自由能、质量作用定律以及超支化高分子的数量分布函数,进而计算了体系的比热和等温压缩系数等热力学量.进一步研究了超支化高分子的空间尺度,给出反应体系k次均方回转半径的递推公式,计算了各种不同溶剂条件下的均方回转半径,指出引发单体分数、反应程度和溶剂效应对超支化高分子空间尺度的影响.     

稀土催化丁二烯顺式聚合过程中的环化改性

采用ＮｄＣｌ３·３ｉ－ＰｒＯＨ－ＡｌＥｔ３稀土催化剂进行丁二烯的顺式聚合，在聚合过程中引入烯丙基氯，进行分子内环化反应以及单体的环聚反应．考察了稀土催化剂用量、ｎ（烯丙基氯）／ｎ（ＡｌＥｔ３）、环化时间、反应温度、单体浓度等对环化反应的影响，并对产物进行了红外光谱、核磁共振光谱的表征     

连锁聚合反应的动态Monte Carlo模拟及其浓度效应

用动态Monte Carlo方法和键长涨落模型相结合分别对自由基聚合、离子聚合动力学过程进行了计算机模拟, 在三维空间中统计了转化率、聚合度、分子量的数量和重量分布, 并将模拟结果和理论预测进行了对比分析, 同时得到不同浓度下均方回转半径与平均链长的标度关系, 说明三维空间中标度指数与浓度的相关性. 还初步考察了扩散对反应体系分子量的影响. 说明动态Monte Carlo方法用于研究连锁聚合反应动力学过程是有效的, 而且能够同时得到经典的聚合反应Monte Carlo模拟方法所难以得到的链构象、分子扩散等空间相关的信息.     

基于格子链的缩聚反应的动态Monte Carlo模拟

采用描述自回避格子链的键长涨落模型, 以动态Monte Carlo方法对AB型单体的线型缩聚反应动力学过程进行了模拟. 通过该方法可以得到反应过程中链的瞬时构象, 还可以得到反应程度、聚合度、分子量分布及其随时间的演化. 模拟得到了合理的结果, 同时验证了无规线团尺寸与平均链长的标度关系, 表明该方法用于研究逐步聚合反应过程是可行的, 并且与一般的研究聚合反应的Monte Carlo方法相比, 还能够同时得到构象等空间信息. 还比较了不同大小的模拟体系所得到的分子量和多分散系数的异同, 讨论了有限元胞效应.     

Kinetics of self‐condensing vinyl hyperbranched polymerization in three‐dimensional space

Self‐condensing vinyl hyperbranched polymerization (SCVP) with A‐B* type monomer is simulated applying Monte Carlo method using 3d bond fluctuation lattice model in three‐dimensional space. The kinetics of SCVP with zero active energy of reaction is studied in detail. It is found that the maximal number–average and weight–average polymerization degrees and the maximal molecular weight distribution, at varying the initial monomer concentration and double bond conversion, are about 52, 190, and 3.93, respectively, which are much lower than theoretical values. The maximal average fraction of branching points is about 0.27, obtained at full conversion at the initial monomer concentration of 0.75. The simulation demonstrated the importance of steric effects and intramolecular cyclization in self‐condensing vinyl hyperbranched polymerization. The results are also compared with experiments qualitatively and a good agreement is achieved. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4486–4494, 2008     

Synthesis of Pyrene‐based Planar Conjugated Polymers and the Regioisomers by Intramolecular Cyclization

Several planar conjugated polymers and model compounds containing pyrene units are synthesized. The precursor polymers and model compounds are obtained through the Pd(0)‐catalyzed Suzuki reaction, then the planar structure is formed through intramolecular cyclization in the presence of acid. We investigate the regioisomers in intramolecular cyclization reaction by using model compounds, suggesting that the syn‐ and anti‐structures are formed in ladder‐type polymer LP1 , and the syn‐structure is more easily formed in LP3 . The planar conjugated polymers and model compounds show untypical features of ladder‐type polymers, they display broad absorption and blue or blue‐green emission in solution, and interchain π‐π stacking in film still occurs. Moreover, the new polymers and model compounds are characterized by nuclear magnetic resonance (NMR) spectroscopy, gel‐permeation chromatography (GPC) and cyclic voltammetry (CV).     

Termination Mechanism in the Anionic Polymerization of Methyl Methacrylate

Recent studies have revealed that at temperatures around 200°K in tetrahydrofuran solvent, poly(methy1 methacrylate) ion pairs are long-lived and very reactive. At higher temperatures however termination of the ion pairs occurs, as evidenced by the broadening of the molecular weight distribution of the resultant polymer and by the incomplete polymerization of the monomer. Three mechanisms have been proposed to describe these termination reactions; an inter molecular reaction with the monomer ester function, an intramolecular cyclization of the anion, or reaction with the polymer ester function. In the absence of monomer only the last two mechanisms can be operative. A series of experiments was undertaken in which the molecular weight distribution broadening with temperature increase was measured under typical polymerization conditions or in the absence of monomer. The effect of each of the three counterions Li, Na, and K was also monitored. The results obtained are discussed in terms of these three possible termination mechanisms. Termination rate constants calculated from the molecular weight distribution are also presented.     

Intramolecular metal—double bond interactions : VII. Intramolecular cyclization of alkenyl derivatives of lithium,aluminum, gallium and indium

The intramolecular cyclization reactions of tri-1-hex-5-enyl Group III derivatives and of 1-hex-5-enyllithium have been investigated and it is proposed that the reactions may be depicted as internal addition across the terminal double bonds of the alkenyl species. The cyclization reaction proceeds more readily for the 1-hex-5-enyl derivatives than for any other chain length and is dependent on temperature, concentration and solvent. ¹H NMR data and cryoscopic molecular weight data are presented for several diisobutyialkenyl- and diisobutylalkyl-aluminum derivatives. These data have been interpreted in terms of a direct intramolecular interaction between the metal center and the π-electron system of the olefinic site. The intramolecular cyclization reactions for the 1-hept-6-enyl, 1-oct-7-enyl- and 1-undec-10-enylaluminum derivatives also were investigated and it was found that cyclization occurred only for the 1-hept-6-enyl derivative.     

Can Flory-Stockmayer theory be applied to predict conventional free radical polymerization of multivinyl monomers? A study via Monte Carlo simulations

The conventional free radical polymerization (FRP) of multivinyl monomers (MVMs) inevitably leads to gelation even at low monomer conversion resulting in difficulties to control and monitor the reaction process. Flory and Stockmayer (F-S theory) studied it based on two fundamental assumptions: (1) independent and equivalent vinyl groups; (2) no intramolecular cyclization. However, until now its applicability to FRP of MVMs (especially regarding the extent of intramolecular cyclization) is still controversial. In this paper, Monte Carlo simulations are used to study FRP of divinyl monomers by two kinetic models: with/without cyclization models. The results of the simulations are compared with the calculated gel points based on F-S theory and the experimental data. It is found that the intramolecular cyclization has a negligible impact on the polymerization process and the gel point before gelation, which are in agreement with the prediction by F-S theory, but the effect becomes significant above the gel points.     

Structure, bonding, and solvation of dilithiodiamines

Computational methods were used to determine the structure of dilithiodiamines and the effects of solvation by ethereal solvents. Solvation was examined by the use of microsolvation with explicit dimethyl ether or THF ligands and by the combined use of microsolvation and the IEFPCM continuum solvent model. It was determined that each of the compounds studied exists exclusively as a bridged intramolecular dimer, both in the gas phase and in solution. Thermodynamic properties were calculated at 200 and 298 K to estimate the effect of temperature on the cyclization energies. Infrared spectroscopy was used to confirm the proposed intramolecular dimer structures.     

Molecular architecture and physicochemical properties of some vinyl alcohol-vinyl acetate copolymers

Two series of vinyl alcohol-vinyl acetate copolymers were prepared by homogeneous and heterogeneous acetylation of the same precursor poly(vinyl alcohol). Their intramolecular monomer distributions were analyzed by IR spectrometry, calorimetry, and differential thermal analysis. The results show a more blocky distribution for the heterogeneously prepared copolymers. The properties of these (co)polymers in dilute aqueous solution were determined by means of viscometry. Whereas the copolymer-solvent interaction parameter of the homogeneously acetylated, random copolymers hardly varied with acetate content, a definite minimum was found for the blocky copolymers at about 7 mole% vinyl acetate. These findings were attributed to the incompatibility of dissimilar sequences, which sharply decreases with decreasing vinyl acetate sequence length. Up to about 17 mole% vinyl acetate content, the solvent quality for the copolymers is at least as good as for poly(vinyl alcohol). In addition, the dilute solution properties of the samples were established in water saturated with 1-butanol. For copolymers with up to about 17 mole% vinyl acetate, at 25°C this mixture is a better solvent than water. The highest increase in solvent quality was found for the homopolymer, whereas the increase diminished with acetate content, irrespective of the intramolecular vinyl acetate distribution. These findings are explained in terms of preferential adsorption of 1-butanol onto the (co)polymer backbone due to hydrophobic interactions and prevention of this process by the bulky acetate groups.     

Cyclopolymerization of diallylcyanamide

A soluble polymer of cyclic structure has been obtained by radical polymerization of diallyleyanamide. A kinetic analysis of the polymerization indicated that the overall rate of the system is first-order with respect to concentration of initiator and either first- or second-order with respect to monomer concentration, depending on the solvent used. The molecular weight of the polymer is independent of the concentration of the initiator and the monomer. The intramolecular abstraction of hydrogen is proposed as a termination reaction.     

Kinetics of nonideal hyperbranched A2 + B3 polycondensation: Simulation and comparison with experiments

To overcome the deficiency of mean field method in introducing the intramolecular cyclization and the steric effects, the reactive bond fluctuation model was applied to study nonideal hyperbranched A₂ + B₃ polycondensation, which has high sensitivity of gelation to the concentration of monomers, the feed ratio and the reactivity of functional groups. Simulation demonstrated that the mean field theory overestimated hyperbranched polymerization especially at high reaction conversion in the system with low monomer concentration where the intramolecular cyclization and the steric hindrance play crucial influences on molecular weight, molecular weight distribution and gel point (GP). The dependences of GP on the monomer concentration, feed ratio, and the reactivity of groups are clearly shown. We further simulated a specific polycondensation system with aromatic terephthaloyl chloride (TCl, A₂) and 1,1,1‐tris(4‐trimethylsiloxyphenyl)ethane (TMS‐THPE, B₃) (Macromolecules 2007, 40, 6846) using fitting technology, and estimated molecular weight, molecular weight distribution, GPs, and the conformation of hyperbanched polymer. It provides a feasible way to quantitatively understand hyperbranched polymerization with the reaction specificity. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Stereochemical aspects of base-promoted reactions of o-alkenyl substituted arylhydrazonoyl chlorides with triphenylphosphine

The title arylhydrazonoyl chlorides treated with Et₃N and PPh₃ give arylazomethyl-enetriphenylphosphoranes and, in some cases, products of intramolecular cyclization (cyclopropacinnolines and benzodiazepines). A high concentration of base and a polar solvent accelerate all the observed reactions. In the presence of PPh₃ a low reaction temperature and a non polar solvent favour the formation of the phosphoranes over the cyclization reaction. The steric configuration of phosphoranes and cyclopropacinnolines is determined by the relative stability of the two isomers.