甲基丙烯酸甲酯聚合动力学和分子量及分布的开放控制

在甲基丙烯酸甲酯聚合过程中 ,凝胶效应会导致转化率在短时间内出现突变 ,这对工业反应器非常危险 ,同时也导致分子量剧增、分子量分布加宽 .为了使聚合反应速度、分子量及分布同时得到控制 ,提出 3个控制目标 ,即热荷分布指数、预定分子量及变化、分子量分布指数 .在甲基丙烯酸甲酯半间歇聚合动力学和分子量模型的基础上 ,通过单体、溶剂和链转移剂 3种物料的流量和加料方式的仿真计算 ,对动力学、分子量及分布进行开放控制 ,并进行优化 ,得到热荷分布指数和分子量分布指数分别小于 2 0和 2 2的控制策略 ,且分子量达到预定要求 .选择两种优化策略进行实验验证 ,结果与开放控制仿真结果一致     

RAFT链转移剂存在下凹凸棒土表面甲基丙烯酸甲酯接枝聚合

将γ-(甲基丙烯酰氧)丙基三甲氧基硅烷(MPS)接枝到凹凸棒土(AT)表面,制得表面带有可聚合碳碳双键的改性粒子AT-MPS;以二硫代苯甲酸氰基异丙酯(CPDB)为链转移剂,采用可逆加成断裂链转移(RAFT)聚合技术,在AT表面进行甲基丙烯酸甲酯(MMA)接枝聚合.通过红外(FTIR)、热失重(TGA)等方法进行了表征,考察了引发剂以及RAFT链转移剂用量对聚合反应动力学和AT表面接枝聚合接枝率的影响.结果表明,PMMA通过RAFT聚合成功接枝在AT表面;基于RAFT过程的接枝聚合比传统自由基接枝聚合具有更长的反应时间和较高的接枝率.本体系相对适宜条件:温度为70℃,[MMA]/[CPDB]/[AIBN]为400/1/0.5.此条件下聚合反应具有很好的可控性,溶液中的聚合物分子量分布指数为1.2~1.3,AT表面PMMA接枝率为16.33%.引发剂和RAFT链转移剂用量过大均会造成接枝率降低.     

等离子体挥发性产物引发甲基丙烯酸甲酯聚合反应动力学

本文发现甲基丙烯酸甲酯等离子体挥发性产物能够有效地引发单体聚合,获得超高分子量聚合物。其聚合过程属于瞬时引发、向单体链转移的活性自由基聚合机理。     

碘代丁烷存在下的甲基丙烯酸甲酯自由基聚合反应

研究了碘代丁烷存在下甲基丙烯酸甲酯在６０℃、以下酮或甲苯为溶剂的自由基聚合。结果表明，１－碘丁烷和２－碘丁烷对ＭＭＡ的聚合无明显影响。以甲苯为溶剂时，碘代叔丁烷既是链转移剂又是链终止剂。     

甲基丙烯酸甲酯水溶性对其悬浮均聚动力学的影响

通过比较在大水油比下的甲基丙烯酸甲酯 (MMA)悬浮均聚的实验数据以及本体聚合实验结果 ,发现单体的水溶性对其聚合动力学有影响 ,不能用本体聚合动力学代替其悬浮聚合动力学 .为了能更好了解单体的水溶性对其悬浮聚合动力学的影响以及影响动力学的原因 ,在MMA本体聚合动力学模型基础上 ,进一步提出 3个假设 :扣除溶于水相部分的单体量、增长和终止速率参数降低、少部分的油溶性引发剂被带到水相中 ,得到改进的悬浮聚合动力学模型 .运用该模型能很好预测水油比、聚合温度、引发剂浓度等对MMA悬浮聚合动力学的影响 ,且与实验数据能较好吻合     

RAFT聚合法合成聚丙烯酰胺基偶氮苯的研究

以二硫代苯甲酸苄酯(BDTB)为链转移剂,偶氮二异丁腈(AIBN)为引发剂,丙烯酰胺基偶氮苯(AAAB)为单体,DMF为溶剂,利用可逆加成-断裂链转移(RAFT)聚合法合成了聚丙烯酰胺基偶氮苯(PAAAB),并考察了聚合温度和链转移剂浓度对聚合反应的影响。通过FT-IR、1 H-NMR、GPC等对链转移剂和聚合物结构进行了表征。结果表明:聚合反应动力学曲线呈良好的线性关系,分子量分布窄;随着[BDTB]/[AIBN]比例的增大,聚合速率和分子量下降,分子量分布变窄。     

β-CD存在下MMA细乳液体系的RAFT聚合

近年来，活性自由基聚合已成为高分子合成领域中的一个热门课题．Rizzardo研究小组提出了一种新型活性自由基聚合反应，即RAFT(Reversible addition-fragmentation chain transfer)聚合．RAFT反应在传统的自由基聚合中加入了具有高链转移常数和特定结构的链转移剂——双硫酯类化合物．当链转移剂的浓度足够大时，链转移反应由不可逆变为可逆，聚合反应也随之发生质的变化，由不可控     

溶剂热体系中甲基丙烯酸甲酯的原子转移自由基聚合

以FeCl3/ PPh3为催化体系,在无引发剂、溶剂热体系中进行甲基丙烯酸甲酯(MMA)的原子转移自由基聚合(ATRP)反应.考察了反应温度与还原剂对反应的影响.实验结果表明,在溶剂热体系中进行的MMA聚合反应符合"活性"/可控聚合,聚合过程中转化率和分子量随时间的增加而增大,所得聚甲基丙烯酸甲酯分子量分布较窄.     

四乙基二氟化氢铵催化的基团转移聚合

用三种引发剂进行了二氟化氢负离子催化的基团转移聚合,得到了窄分布的,实测分子量和理论分子量相近的一系列聚甲基丙烯酸酯产物,合成了分子量达20万以上的聚甲基丙烯酸甲酯,探讨了引发剂和催化剂用量对产物的分子量和分散性的影响,认为过量的催化剂使产物的分散性加大和实测(?)_n大于理论M_n。得到了控制聚合的最佳催化剂和引发剂浓度比。     

丙烯酰胺基偶氮苯的RAFT聚合反应动力学

以丙烯酰胺基偶氮苯(AAAB)为单体,二硫代苯甲酸异丙苯酯(CDB)为链转移剂,偶氮二异丁腈(AIBN)为引发剂,N,N-二甲基甲酰胺(DMF)为溶剂,利用可逆加成-断裂链转移(RAFT)聚合法合成了侧链含有偶氮苯基团的聚丙烯酰胺基偶氮苯(PAAAB),同时考察了反应温度、引发剂浓度、链转移剂浓度等因素对聚合反应的影响。利用FT-IR、1H NMR、GPC等对其结构进行了表征。结果表明,聚合反应动力学曲线呈良好的线性关系,分子量分布窄;随着[CDB]/[AIBN]比例的增大,聚合速率、分子量和分子量分布均下降。     

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.     

The effect of Co(II)‐mediated catalytic chain transfer on the emulsion polymerization kinetics of methyl methacrylate

The effect the catalytic chain transfer agent, bis[(difluoroboryl) dimethylglyoximato] cobalt(II) (COBF), on the course of the ab initio emulsion polymerization of methyl methacrylate, and the product properties in terms of the molecular weight distribution were investigated. The emulsion polymerization kinetics have been studied with varying surfactant, initiator, and COBF concentrations. The experimentally determined average number of radicals per particle strongly depends on the concentration of COBF and proves to be in good agreement with the results of model calculations. The apparent chain transfer constant, determined up to high conversion, is in excellent agreement with the predicted value based on a mathematical model based on COBF partitioning and the Mayo equation. The results of this work enhance the fundamental understanding of the influence a catalytic chain transfer agent has on the course of the emulsion polymerization and the control of the molecular weight distribution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5078–5089, 2009     

The Role of a Metallocene Additive in Radically Initiated Polymerization when Solving Direct and Inverse Kinetic Problems

Polymerization of methyl methacrylate, initiated by benzoyl peroxide in the presence of titanocene dichloride, is considered from the point of view of formal kinetics. Based on the kinetic scheme of the process (which includes the reactions of classical radical polymerization, the reaction of benzoyl peroxide with titanocene dichloride, the reactions of the controlled radical polymerization of organometallic mediated radical polymerization (OMRP) and atom transfer radical polymerization (ATRP), the reaction of the formation of a coordinating active site and the coordinating chain propagation on a mathematical model of the kinetics of the process is created. This model also makes it possible to calculate the molecular-mass characteristics of poly(methyl methacrylate). As a result of the solution of the inverse kinetic problem at a temperature of 343 K, the values of the reaction rate constants of the kinetic scheme are found under which the discrepancy between the calculated models and experimental data is minimal. Using the developed model of the kinetics of the process, a numerical experiment is performed (i.e., a direct kinetic problem is solved). This problem revealed the following regularities of the process. (1) An increase in the initial concentration of titanocene dichloride at a constant initial concentration of benzoyl peroxide leads to an increase in the rate of consumption of benzoyl peroxide but not to an increase in the initial rate of the process compared to classical radical polymerization. (2) With an increase in the initial concentration of titanocene dichloride, the lifetime of the macroradicals at the initial stage of the process is reduced, and hence the molecular weight of the resulting polymethyl methacrylate is less than that of the polymethyl methacrylate obtained in the absence of titanocene dichloride, and it will increase during the process of approaching the final values. (3) During the polymerization of methyl methacrylate, initiated by benzoyl peroxide in the presence of titanocene dichloride, a smoothing gel effect (as in the case of the polymerization of methyl methacrylate initiated by benzoyl peroxide in the presence of ferrocene) does not occur since titanocene dichloride forms stable complexes with methyl methacrylate and, consequently, it participates in reactions consuming macroradicals to a lesser degree than ferrocene.     

Kinetic modeling of two-step RAFT process for the production of novel fluorosilicone triblock copolymers

Well-defined poly(dimethylsiloxane)-b-poly(2,2,3,3,4,4,4-heptafluorobutylmethacryl-ate-b-poly(styrene) (PDMS-b-PHFBMA-b-PS) triblock copolymers were prepared by two-step reversible addition-fragmentation chain transfer (RAFT) polymerization. A comprehensive mathematical model for the two-step RAFT polymerization in a batch reactor was presented using the method of moments. The model described molecular weight, monomer conversion and polydispersity index as a function of polymerization time. Good agreements in the polymerization kinetics were achieved for fitting the kinetic profiles with the suggested model. In addition, the model was used to predict the effects of initiator concentration, chain transfer agent concentration and monomer concentration on the two-step RAFT polymerization kinetics. The simulated results showed that for the two-step RAFT polymerizations, the effects initiator concentration, chain transfer agent concentration and monomer concentration are identical and the influence degrees are different yet.     

Effect of Stabilizer Concentration,Pressure and Temperature on Polymerization Rate and Molecular Weight Development in RAFT Polymerization of MMA in scCO2

Summary: An experimental study on the effect of stabilizer concentration, pressure (100 to 500 bar), and temperature (65 to 85 °C) on polymerization rate and molecular weight development in the reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) in supercritical carbon dioxide (scCO₂) is presented. AIBN was used as initiator, S-Thiobenzoyl thioglycolic acid as RAFT agent, and Krytox® 257 FSL as stabilizer. It was observed that the polymerization proceeded in a controlled manner. High conversions can be reached in reasonable times. Fairly low polydispersities (around 1.2) are possible if either pressure or temperature are increased, but better results are obtained if the polymerization proceeds at the upper temperature value of 85 °C.     

Effect of 1-n-Dodecanethiol on the Molecular Weight Distribution of Poly(methyl Methacrylate) Synthesized by Suspension Polymerization

Fractionation data of two poly(methyl methacrylate) samples prepared by suspension polymerization up to limiting conversion, in the presence of different amounts of 1-n-dodecanethiol, indicate that both samples have similar polydispersity factors, although the molecular weight distribution curve for the sample obtained with the highest chain transfer agent concentration is shifted to lower molecular weight values. The results obtained are qualitatively correlated with the high conversion polymerization theory proposed by Cardenas and O'Driscoll.     

Reversible Addition-Fragmentation Chain Transfer Polymerization of Methyl Methacrylate in Microemulsion: The Influence of Reaction Conditions on Polymerization

The reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) using cetyltrimethylammonium bromide (CTAB) as surfactant and a difunctional RAFT agent S,S′-bis (α, α′-dimethylacetic acid) trithiocarbonate (BDAT) as chain transfer were conducted in microemulsion. The influence of polymerization temperature and concentration of RAFT agent on the polymerization were investigated, respectively. The results showed that the molecular weight of products increased linearly with conversion, the polydispersity indexes remained low value, and the polymerization processes were totally under control with increasing concentration of RAFT agent, the polymerization behavior exhibited living polymerization characters. In addition, the influence of RAFT concentration on the particle size was investigated by TEM. The results indicated that the particles were highly monodispersed and the particle size increased with increasing concentration of RAFT agent.     

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.     

Reversible addition-fragmentation chain transfer polymerization in microemulsion

This tutorial review first details the uncontrolled microemulsion polymerization mechanism, and the RAFT polymerization mechanism to provide the necessary background for examining the RAFT microemulsion polymerization mechanism. The effect of the chain transfer agent per micelle ratio and the chain transfer agent aqueous solubility on the RAFT microemulsion polymerization kinetics, polymer molecular weight and polydispersity, and polymer nanoparticle size are discussed with a focus on oil-in-water microemulsions. Modeling of RAFT microemulsion polymerization kinetics and the resulting final polymer molecular weight are presented to assist with the analysis of observed experimental trends. Lastly, the current significance of RAFT microemulsion polymerization and the future directions are discussed.