自由基聚合速率的深入讨论

自由基聚合是高分子化学课程中的重要一章,自由基聚合动力学(包括聚合速率、平均相对分子质量及分布)是教学中的重要内容。本文讨论了建立自由基聚合微观动力学模型的基础:三个基本假设和四个简化条件,阐释了传统单官能度引发剂引发的聚合体系速率方程推导中这些假设和条件的运用,并扩展到双官能度引发剂体系,得到基元反应速率和总速率。提出从三个层次讨论影响自由基聚合速率的因素,深化了对自由基聚合速率教和学。     

动力学链长与平均聚合度、自由基寿命之间的关系

自由基聚合是《高分子化学》学习的重要内容，其中动力学链长、平均聚合度、自由基寿命是三个重要的学术概念，理清三者之间的定量关系以于自由基聚合的理论学习颇有帮助。本文试图对这一内容进行讨论。     

药学专业高分子化学的虚拟仿真教学探索——基于Python的自由基聚合反应模拟

通过Python语言开发了一款教学用自由基聚合反应数值模拟器FRPython。该程序通过对自由基聚合反应体系的常微分方程组进行数值模拟,得到引发剂自由基浓度、链自由基浓度、动力学链长,以及聚合度分布等信息。以聚甲基丙烯酸甲酯聚合体系的数值模拟为例,FRPython可直观有效地演示自由基聚合反应过程,同时避免了稳态假设、方程推演等较为深奥的内容,为药学专业高分子化学相关知识的教学提供有益参考。     

自由基聚合的模块化教学及难点剖析

自由基聚合作为高分子化学的重点内容,内容丰富,难点较多。本文拟对作者在教学过程中总结的模块化教学方法进行介绍,并尝试对自由基聚合的动力学链长、聚合度及链转移这一难点内容进行剖析。     

不同聚合机理的“平均聚合度”公式的分析讨论

平均聚合度和聚合度分布是决定聚合物产品质量的一个重要指标。平均聚合度直接表征聚合产品的分子量的大小,它的大小又决定高分子材料的性能,因此,研究平均聚合度具有重要的理论意义和实际意义。聚合反应按机理分类,可分为链型聚合和逐步聚合,链型聚合又分为自由基聚合、离子聚合、配位聚合,逐步聚合又分为缩聚和加聚反应。本文以自由基聚合、离子聚合、配位聚合以及缩聚的聚合机理为主线,对不同聚合机理对应的平均聚合度的公式进行推导和讨论,并加深理解,掌握其内涵。旨在提高学生对平均聚合度的认识和把握。     

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.     

自由基聚合中平均聚合度的学习

自由基聚合是《高分子化学》课程的重要一章 ,其中 ,平均聚合度是自由基聚合微观动力学的重要研究内容。正确理解其概念 ,掌握各种数学表达式的涵义 ,对高分子化学的学习十分有益 ,本文对不同终止和链转移情况下平均聚合度的表述方法进行了讨论     

不同聚合机理的“聚合度”公式的讨论

从聚合反应的机理的角度,聚合反应分为逐步聚合和连锁聚合两类.连锁聚合按照引发"活性种"的差异又分为自由基聚合和离子聚合.离子聚合分为阳离子聚合、阴离子聚合和配位聚合.这些是所有<高分子化学>教材编排的重要线索.本文以自由基聚合、离子聚合、逐步聚合和配位聚合的机理为线索,进一步说明对<高分子化学>教材中关于聚合度公式的综合理解和融会,旨在提高学生对<高分子化学>重点内容和意义的认识和把握.     

从聚氯乙烯攻关任务到聚合反应工程基础研究

根据十多项聚氯乙烯国家攻关任务,抽提出聚合反应工程基础研究课题。融合聚合化学、工艺、工程三方面内容,提出聚合机理和成粒机理两条主线,深入研究聚合速率、聚合度、共聚物组成等动力学问题,悬浮和微悬浮聚合的微观和宏观成粒机理,以及聚合釜传热、搅拌混合和放大技术,而后更有效地解决聚氯乙烯新品种开发和聚合釜放大设计中的关键问题。     

阴离子聚合教学中几个难点的解析

阴离子聚合是高分子化学教学中的重要内容,正确理解阴离子聚合的有关概念,掌握利用活性阴离子聚合的机理特征处理阴离子聚合动力学,对阴离子聚合的学习十分有益.本文针对阴离子聚合中烯类单体结构特点、阴离子引发剂与单体匹配本质、活性阴离子聚合动力学中聚合速率、聚合度及聚合度分布等重难点内容作了较深入的分析,其中利用单体成键概率p...     

Vinyl polymerization initiated by peroxydiphosphate

The kinetics of the aqueous polymerization of acrylonitrile and methyl methacrylate initiated by the peroxydiphosphate-thioglycollic acid redox system was investigated at 40, 45, 50, 55, and 60 °C. The rates of polymerization were measured at different concentrations of oxidant, activator and monomer. From the results, it was concluded that the polymerization reaction is initiated by an organic free radical arising from the peroxydiphosphate-thioglycollic acid system and termination by mutual type. On the basis of experimental observations of the dependence of the rate of polymerization,R _p on various variables, a suitable kinetic scheme has been proposed.     

双官能度引发剂引发苯乙烯聚合微观动力学

采用 2 ,5 二甲基 2 ,5 二己酰基过氧化己烷 (DMDEHPH)为引发剂 ,在 5 5～ 80℃下引发苯乙烯聚合 .通过研究影响聚合速率的各种因素 ,得出了聚合速率对单体浓度和引发剂浓度的级数分别为 1 0和 0 5次、聚合活化能为 92 0kJ mol、引发效率为 0 5 5± 0 0 3.温度一定 ,引发效率随引发剂浓度的增加而减小 .求得 6 0和70℃下DMDEHPH向引发剂的链转移常数分别为 0 0 37和 0 0 4 8、向单体的链转移常数分别为 0 5 9× 10 - 4和0 75× 10 - 4.     

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.     

Catalyzed chain transfer to monomer in free radical polymerization

The kinetics and the molecular weight distribution in the radical polymerization of methyl methacrylate in the presence of a cobalt complex of hematoporphyrin tetramethyl ether is investigated. The whole complex of experimental data indicates the new kinetic phenomenon—catalyzed chain transfer to monomer. The possible mechanism of the chain transfer and the chain transfer agent regeneration acts is suggested.     

Polymerization processes at conditions of moderately short kinetic chains by calorimetry

A method has been developed for the determination of the heat of the acts of chain growth q_g and of the summary heats of the acts of chain initiation and termination q^** for the radical polymerization of vinyl monomers at the conditions of moderately short kinetic chains, when the length of the kinetic chain v < 100, but the degree of polymerization is ¯P > 20. The analysis of the experimental data, obtained by investigating the kinetics of polymerization of vinyl monomers in solution by calorimetry has led to the conclusion, that at v > 100 an approximation of the long material chains can be used (when the contribution of q^** is negligibly small) with a permissible experimental error; however, in the region of moderately short chains a correction for q^** must be introduced, in order to obtain the correct kinetics of the process.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 695–701, November–December, 1988.     

Kinetics of polymerization reactions with reversible-chain termination

General kinetic features of radical and ionic polymerization processes accompanied by reversible chain termination reactions are considered. Special attention is paid to the conditions of applicability of the steady-state approximation usually employed to analyze the kinetics of radical polymerization. It is shown that the steady-state concentration of radicals is attained at practically the very beginning of the reaction, while the steady-state concentration of a reversible termination agent is reached with a certain delay. A kinetic explanation of the reversible termination reaction effect on the pattern of the molecular-mass distribution is suggested. Conditions providing the obtainment of a polymer with a narrow molecular-mass distribution in processes with reversible termination are formulated.     

Kinetics and Mechanism of the Polymerization of Methyl Methacrylate in a Y(acac)3/n-BuMgCl System

Based on the kinetics equation proposed by T. Kagiya, the kinetic study on the polymerization of methyl methacrylate(MMA) by Y(acac)3/n-BuMgCl was carried out with a dilatometer. It was found that the rate of propagation is the first order with respect to the concentration of both active center and monomer. Thus, the equation of propagation rate can be described as Rp=Kp[c*][M]. In addition, the instantaneous chain initiation and single molecular termination were concluded for the present system. The activation energy is close to 32 kJ/mol. In the polymerization, n-BuMgCl acts not only as the cocatalyst, but also as chain transfer agent with cI=3.6×10-4.     

The effect of the resultant microphase-separated structures of polymer matrices on the electro-optical properties of polymer dispersed liquid crystal films by Iniferter polymerization

Iniferter polymerization was employed to prepare polymer dispersed liquid crystal (PDLC) films and an additional photoinitiator was introduced to induce the phase separation of polymer matrices themselves on the process of preparing the PDLC. The effect of the polymerization kinetics and the resultant microphase-separated structures of polymer matrices on the electro-optical properties of PDLC films were studied. It was found that the bigger length scale of phase separation of polymer matrices induced strong light-scattering resulting in low ON-state transmittance. And faster polymerization kinetic induced higher threshold and saturation voltages.