Kinetics of Radical Polymerization. XXIX. Kinetics of Initiation in the Polymerization of Ethyl Acrylate

The rate of initiation has been investigated in the free-radical polymerization of ethyl acrylate at 50°C in two solvents, benzene and dimethylformamide. The rate constant of initiation and the rate constant of the decomposition of AIBN was determined by the inhibition method and nitrogen volumetry, respectively. The rate constant of initiation was found to be constant over the whole range of monomer concentration in benzene solutions, but it proved to depend on the concentration of monomer in dimethylformamide solutions. The latter dependence is not linear. It was pointed out that the change in the rate constant of initiation is due to the solvent effect on the rate constant of decomposition of AIBN, because the factor of radical efficiency is practically constant over the whole range of monomer concentration. The observed relationship between the rate constant of initiation and the molar fraction of monomer was interpreted on the basis of the selective solvation of initiator molecules.     

Polymerization Kinetics of n-Lauryl Acrylate

The polymerization kinetics of n-lauryl acrylate have been investigated in ethyl acetate and n-heptane at 40°C. A high monomer order, 1.6(5), was found in both solvents. Corresponding initiator orders, determined using Azdn and lauroyl peroxide, were slightly less than the usual value of 0.5. Although the chain termination reaction is undoubtedly diffusion controlled from the start of polymerization, diffusion effects dependent on monomer concentration only partly account for the high monomer order. Other possible explanations based on primary radical termination, “cage-effects,” degradative chain transfer, and radical complexing are also not applicable. Contrary to observations with lower acrylate esters, autoacceleration effects do not occur in the high conversion polymerization of n-lauryl acrylate. Ths probably reflects the reduced importance of radical branching reactions with this monomer.     

一氯代八甲基环四硅氧烷阳离子聚合动力学

合成了八甲基环四硅氧烷的一氯取代物,并以其为单体,98%浓硫酸为催化剂,采用称重法研究了一氯代八甲基环四硅氧烷阳离子开环的本体聚合动力学,探讨了温度,催化剂浓度对其聚合速率常数的影响.研究表明:温度,催化剂浓度对一氯代八甲基环四硅氧烷的聚合速率有显著影响,其聚合活化能是40.37kJ.mol-1;与八甲基环四硅氧烷阳离子开环聚合相比,氯代甲基使硅氧烷的开环聚合速率减慢,聚合活化能升高.     

Fundamentals of RAFT Miniemulsion Polymerization Kinetics

Summary: The polymerization rate of RAFT-mediated miniemulsion polymerization, in which the time fraction of active radical ϕ_A is larger than a few percent, basically increases with reducing the particle size. For smaller particle sizes, however, the statistical variation of monomer concentration among particles may slow down the polymerization rate. The rate retardation by increasing the RAFT concentration occurs with or without the intermediate termination in a zero-one system. According to the present theoretical investigation, smaller particles are advantageous in implementing a faster polymerization rate, a narrower MWD, and a smaller number of dead polymer chains.     

Kinetics and Mechanism of Radical Polymerization

Low molecular reactions are frequently accompanied by side reactions producing a whole spectrum of by-products whose removal in purification operations generally causes little difficulty because the major and side products usually differ sufficiently in their properties. Hence detailed kinetic studies in low molecular chemistry can claim industrial interest only insofar as they aim to reduce the rate of formation of side products. The situation is completely different in polymer chemistry, where the terms major and side product no longer apply. Instead, one obtains mixtures of similar and/or isomeric molecules which differ so little with regard to molecular weight and structure that resolution into pure substances or isolation of pure substances becomes practically impossible. However, since all partial reactions exert a direct influence on the product spread, i.e. the composition and properties of a product mixture are modified by any change in operating conditions, detailed kinetic analyses embracing all relevant partial reactions are an essential prerequisite for the production of defined polymeric products on any scale. This progress report illustrates the importance of kinetics for radical polymerization with the aid of selected examples.     

聚合动力学研究方法进展

从构造聚合动力学模型所采用的数学方法出发 ,对聚合动力学模型———概率统计模型、机理模型及基于MonteCarlo模拟模型等的进展进行了综述。     

Study on the Kinetics of Polymerization of Tributyltin Methacrylate

The kinetics of polymerization of tributyltin methacrylate (TBTM) has been studied in benzene solution in the temperature range 60–75°C in the presence of azobisisobutyronitrile (AIBN). We have obtained the following polymerization rate equation: R _p = K _p [TBTM]^1.5 [AIBN]^0.5. It shows that the dependence of the polymerization rate on the concentrations of the monomer TBTM and the initiator AIBN are 1.5 and 0.5 order, respectively. The activation energy of polymerization was found to be 18.1 kcal/mol. The activation energy for the degree of polymerization is approximately -12.3 kcal/mol.     

Model for Kinetics of Vinyl Chloride Polymerization

This paper gives a critical review of recent models for the polymerization of vinyl chloride. In solution and bulk polymerization the effect of eventual degradative chain transfer to monomer, addition of chain transfer agents, and precipitation of polymer is discussed. A model for emulsion polymerization is described which includes particle formation and kinetics of polymerization where especially desorption and reabsorption of radicals in the particles are included.     

Molecular Versus Conventional Kinetics of Emulsion Polymerization

Summary: Experimental data are discussed challenging the deterministic kinetics of emulsion polymerization. Examples are given for the overall rate of polymerization, in-situ stabilizer formation, and swelling of latex particles. Improving the deterministic view on emulsion polymerization kinetics requires the consideration of results of molecular modelling and the application of multiscale integration techniques.     

A Study of L-Lactide Ring-Opening Polymerization Kinetics

Summary: The paper presents an experimental study of L-lactide polymerization in molten state using as initiator the Stannous Octoate. The experiments were performed in a Haake mixer. The operating temperatures were between 170 and 195°C, the reaction time up to 60 min and monomer to initiator initial molecular ratio between 10² and 5 · 10³. The conversion was determined by using ¹H NMR and the molecular weights distributions by SEC. A preliminary mathematical modeling study was also performed, based on experimental data and a previously published reaction scheme.     

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。     

RAFT Miniemulsion Polymerization Kinetics, 1 – Polymerization Rate

The polymerization kinetics of a RAFT‐mediated radical polymerization inside submicron particles (30 < D_p < 300 nm) is considered. When the time fraction of active radical period, ϕ_A, is larger than ca. 1%, the polymerization rate increases with reducing particle size, as for the cases of conventional emulsion polymerization. The rate retardation by the addition of RAFT agent occurs with or without intermediate termination in zero‐one systems. For the particles with D_p < 100 nm, the statistical variation of monomer concentration among particles may not be neglected. It was found that this monomer‐concentration‐variation (MCV) effect may slow down the polymerization rate. An analytical expression describing the MCV effect is proposed, which is valid for both RAFT and conventional miniemulsion polymerizations.

     

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.     

脉冲激光引发自由基聚合的动力学研究

处理了无链转移时脉冲激光引发自由基聚合中的动力学问题:推导出聚合产物数均和重均分子量的严格数学表达式,给出了链自由基、死聚物及总的聚合产物的归一化的分子量分布函数,计算结果表明:随着单体转化率的上升,各种分子参数,例如数均和重均分子量,以及多分散指数的数值周期性地振荡,且振幅逐渐下降,分子量分布曲线则包含一些特征峰,且随着每次脉冲激光产生的初级自由基浓度的降低,分布曲线峰的数目增加,另外,与歧化终止相比,偶合终止使产物的分子量分布略为变窄.     

氯丁胶乳乳液接枝甲基丙烯酸甲酯的反应动力学

采用乳液聚合法将甲基丙烯酸甲酯(MMA)接枝到氯丁胶乳上,红外光谱和核磁共振氢谱证实了接枝产物的生成。 研究了反应温度、乳化剂浓度、引发剂浓度和单体浓度对表观聚合速率的影响。 结果表明,当反应温度为50 ℃,引发剂叔丁基过氧化氢 四乙烯五胺（t-BHP/TEPA）用量为氯丁胶乳干重的0.5%,单体/聚合物质量比m(M)∶m(P)=3∶5,乳化剂十二烷基连苯醚二磺酸钠（DSB）用量为单体总质量1%时,单体转化率和接枝效率分别为99.1%和54.9%。 聚合反应动力学关系式为：Rp=Kc(E)0.15c(I)0.30c(MMA)1.41,式中,K为常数,在40~55 ℃范围内,聚合反应的表观活化能Ea＝60.2 kJ/mol。 接枝聚合基本符合自由基反应机理。     

关于八甲基环四硅氧烷乳液聚合反应动力学的回归模拟

本文用数值逼近法对八甲基环四硅氧烷乳液聚合反应的实验结果进行模拟,得到一符合实验事实的动力学方程.     

二苯甲烷二异氰酸酯(MDI)聚合反应动力学研究

采用TG-DSC-DTG技术研究了二苯甲烷二异氰酸酯(MDI)在流动高纯氮气中的聚合反应动力学. 利用Flynn-Wall-Ozawa法进行了非等温动力学计算, 得到了MDI聚合反应的动力学参数, 通过Satava-Sestak法、Coats-Redfern法对不同机理模型进行选取, 确定了MDI聚合反应的机理为随机成核和随后生长模型, 机理函数为 . 由以上三种方法计算结果表明: MDI聚合反应的表观活化能E＝58.42 kJ•mol^－1, 指前因子A＝ 5006 min^－1, 动力学方程为: [－ln(1－α)]^1/2＝5006exp(-58.42*1000/8.314T)t.     

新型引发剂引发苯乙烯聚合的动力学

采用过氧化2-乙基己基碳酸叔丁酯为引发剂,研究了苯乙烯自由基本体聚合的动力学过程,考察了引发剂浓度、温度、乙苯质量分数对聚合反应速率和聚苯乙烯分子量的影响.结果表明:在117℃下,聚合速率(Rp)对引发剂浓度的反应级数为0.42,对苯乙烯浓度的反应级数为1,聚合反应的表观活化能为54.8 kJ/mol.引发剂浓度、温度、乙苯质量分数的提高导致聚苯乙烯数均分子量分别下降了约30％、20％和15％,其中引发剂浓度的影响最为显著.