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。     

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。     

浅谈自由基聚合动力学的教学与学习

自由基聚合动力学是高分子化学教学和学习中的重要内容。本文讨论了建立自由基聚合微观动力学模型的三个简化条件和三个基本假设,三个简化条件和三个基本假设是微观动力学研究聚合速率和聚合度的基础;同时也较为深入地探讨了动力学链长的物理意义、利用动力学链长概念建立起来的平均聚合度计算通用公式以及该公式的使用条件。     

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.     

对《高分子化学》课程中若干难点的教学体会

针对《高分子化学》课程教学中的一些疑难问题,如丙烯的聚合能力、自由基聚合终止反应动力学方程中的系数、从聚合度分布函数推导平均聚合度、缩聚反应中“摩尔系数”的定义和可控活性聚合等,介绍了本人的理解和教学经验。     

对自由基聚合反应中两种情况下聚合度分布的探讨

自由基聚合是高分子化学学习中的重难点。聚合速率、聚合度与聚合度分布都是重要的学习内容,偶合终止、歧化终止及链转移都会使聚合度的分布有差异,且相关文献和教材在链转移情况下对聚合度分布的影响分析的较少,本文从自由基聚合度推导方法出发,对自由基聚合涉及不同终止方式及链转移情况下的聚合度分布进行探讨。本文侧重于对存在链转移的情况下的两种计算方式进行详细地分析,并与实验结果进行对比,从而说明两种计算方式的特点和造成偏差的原因,得出了详细的理论结果,以有助于初学者更好地理解和研究该部分的相关内容。     

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。     

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。     

《高分子化学》课程中“活性自由基聚合”的教学实践

《高分子化学》课程是五大化学基础课程(无机化学、有机化学、分析化学、物理化学、高分子化学)之一,是化学类、高分子材料与工程、材料化学专业的必修课程。"活性"/可控自由基聚合是一种相对较新且重要的聚合物合成技术和方法,针对目前《高分子化学》课程中活性自由基聚合的教学比较薄弱的现状,从教学的角度探讨了活性聚合和可控/"活性"自由基聚合的本质和特点,介绍了本人在这方面的教学实践活动,遵循成果导向教育理念,通过以学为中心的教学方式,打造金课,提高教学质量。     

有关缩聚反应聚合度公式的讨论

聚合度计算公式是缩聚反应一项重要的学习内容,对学生来说是一个学习难点。针对这一问题,本文对缩聚反应的五个聚合度公式进行讨论,并结合实例来说明如何选用合适的聚合度公式,希望对有关的教与学有所启发。     

Kinetics of Living Polymerization with Propagation Rate Constants Depending on Degree of Polymerization

A study is presented on the kinetics of living polymerization in which the propagation rate constants decrease to zero at a certain degree of polymerization of the propagating chain. The general solution for the distribution function and the rate of polymerization is given and two special cases are discussed. When all the propagation rate constants are the same up to a critical degree of polymerization and null beyond it, the polymerization proceeds approximately as a normal living polymerization until the number-average degree of polymerization reach 85 to 90% of the critical value. When the propagation rate constants decrease linearly with the degree of polymerization, the distribution of living polymer is narrower than the usual Poisson distribution and the reaction order of the rate of polymerization with respect to monomer concentration is between first and second and is affected by the initial monomer and catalyst concentrations.     

Butyllithium Polymerization of Butadiene. II. Effects of Solvent and Temperature on Association of Polybutatadienyl Lithium

Abstract

In the butyllithium polymerization of butadiene in aliphatic solvents at 25°C, the first few monomer units are incorporated largely in a 1, 2 manner. With increasing degree of polymerization the extent of 1, 2 addition decreases to a limiting value of about 10% at a degree of polymerization of about 50. However, within this region of high 1, 2-addition increasing solvent basicity, i.e., changing from aliphatic to aromatic solvents, markedly reduces extent of 1, 2 addition and also narrows the molecular weight distribution. Further, in aliphatic solvents, increasing polymerization temperature from 25 to 60°C also results in a marked reduction in 1, 2 addition. These results are consistent with the concept that an ion pair of the associated organolithium complex, [R (_n-1 Li_n] ⊕R?, is the active polymerization species and that changes in mode of monomer incorporation are due to changes in the degree of association of the entire organolithium system.     

A General Autofluorescence Method to Characterize Polymerization Progress

An autofluorescence technique to characterize polymerization progress in real time/in line was developed, which functioned in the absence of typical fluorogenic groups on the monomer or polymer. The monomer dicyclopentadiene and polymer polydicyclopentadiene are hydrocarbons that lack traditional functional groups for fluorescence spectroscopy. Here, the autofluorescence of formulations containing this monomer and polymer during ruthenium-catalyzed ring-opening metathesis polymerization (ROMP) was harnessed for reaction monitoring. The methods fluorescence recovery after photobleaching (FRAP) and here-developed fluorescence lifetime recovery after photobleaching (FLRAP) characterized polymerization progress in these native systems—without requiring exogenous fluorophore. (Auto)fluorescence lifetime recovery changes during polymerization correlated linearly to degree of cure, providing a quantitative link with reaction progress. These changing signals also provided relative rates of background polymerization, enabling comparison of 10 different catalyst-inhibitor-stabilized formulations. Multiple-well analysis demonstrated suitability for future high-throughput evaluation of formulations for thermosets. The central concept of the combined autofluorescence and FLRAP/FRAP method may be extendable to monitoring other polymerization reactions previously overlooked for lack of an obvious fluorescence handle.     

Polymerization with organoboron compounds

In the presence of organoboron compounds, free-radical polymerization of vinyl monomers can proceed in spite of the presence of excess of typical radical inhibitors. The concept of free radical–organoboron complex formation is introduced to explain the unique role of organoboron compounds in such a polymerization system.     

Vinyl Polymerization. 374. Radical Polymerization of Vinyl Monomer Initiated with Sodium Polystyrenesulfonate

The polymerization of vinyl monomer initiated by an aqueous solution of sodium polystyrenesulfonate (PSS-Na) was carried out at 85°C. Methyl methacrylate (MMA) and styrene were polymerized, while acrylonitrile was not. The rate of polymerization of MMA decreased with the increase of the degree of polymerization of PSS-Na. However, the polymerization was not initiated by sodium ethyl benzenesulfonate which was a unit molecule of PSS-Na. The polymerization proved to be a radical reaction. The polymerization was considered to commence with the formation of hydrophobic areas with PSS-Na in the aqueous phase. MMA is incorporated into these areas, and there the polymerization is initiated and proceeds. The hydrophobic areas were assumed to be similar to the micelles formed by anionic detergents such as sodium alkylbenzene sulfonate. An initiation mechanism is proposed.     

线型缩聚反应的计算机模拟

缩聚反应是一类重要的高分子合成方法。其中最简单的反应为线型缩聚体系,它可分为两类,分别是含有两个可缩合的官能团的单体或单体对进行的相互缩合的体系。Flory在上世纪四十年代采用统计方法对该缩聚体系做过系统的理论研究,并在官能团等活性的假定下提出了著名的Flory分布函数,由此揭示了反应体系中数均聚合度xn、重均聚合度xw、不同聚合度分子的分布情况与反应程度p的关系。本文利用计算机模拟的方法,同样在官能团等活性的假定下模拟了线性缩聚反应的全反应过程,所得到的结果与用统计方法所得到的结果完全一致。本方法是对整个真实反应过程的直观模拟,对研究相似的以逐步聚合反应机理进行的反应具有普适性,并具有可拓展到模拟更真实的粘性聚合体系以及研究反应动力学的潜力。