Non-seeded semi-continuous emulsion polymerization

Semi-continuous emulsion polymerization of acrylic monomers was investigated from the point of view of the particle growth. In the process no seed latex was used and the monomers were fed in an emulsion form. Oscillations of surface tension and particle number indicated a periodical generation and flocculation of particles during the polymerization. Investigation of particle size and molecular weight changes in the first tens of seconds of polymerization has shown that the coagulation process proceeds even in the earliest stage of the polymerization. Initial emulsifier concentration in the reactor strongly affects the particle growth and the final particle number.     

Microemulsion polymerization of butyl acrylate. IV. Effect of emulsifier concentration

The oil/water microemulsion polymerizations of butyl acrylate initiated by a water (ammonium peroxodisulfate, APS) or oil (dibenzoyl peroxide, DBP) soluble radical initiator at different emulsifier concentrations were investigated. The rate of polymerization vs. conversion curve shows two intervals. The rate of polymerization is found to decrease with the emulsifier concentration. This finding was discussed in terms of the decrease of both radical and monomer concentration, the chain transfer to emulsifier, desorption of chaintransferred radicals, and the contribution of solution polymerization. The polymerization is faster with APS. In the APS system the rate per particle or the number of radicals per particle increases exponentially with increasing particle size. The particle size and number increase during the whole polymerization. This behavior was discussed in terms of the nucleation of monomer-containing micelles and agglomeration of primary particles during the whole polymerization. © 1995 John Wiley & Sons, Inc.     

悬浮-乳液复合聚合聚苯乙烯-聚甲基丙烯酸甲酯复合粒子的颗粒特性和成粒机理

采用在苯乙烯 (St)悬浮聚合过程中滴加甲基丙烯酸甲酯 (MMA)乳液聚合组分的悬浮 乳液复合聚合方法 ,制备大粒径聚苯乙烯 聚甲基丙烯酸甲酯 (PS PMMA)复合粒子 .研究聚合物粒径分布和颗粒形态的变化发现 ,在St悬浮反应中期滴加MMA乳液聚合组分后 ,聚合体系逐渐由悬浮粒子与乳胶粒子并存向形成单峰分布复合粒子转变 ,最终形成核 壳结构完整的大粒径PS PMMA复合粒子 ;在St悬浮反应初期滴加MMA乳液聚合组分 ,St与MMA一起分散成更小液滴 ,反应后期凝并成非核 壳结构复合粒子 ;在St悬浮反应后期滴加MMA乳液聚合组分 ,PMMA乳胶粒子与PS悬浮粒子基本独立存在 .根据以上结果 ,提出了St MMA悬浮 乳液复合聚合的成粒机理 .     

Formation of monodisperse polyacrylamide particles by radiation-induced dispersion polymerization: particle size and size distribution

Polyacrylamide microparticles were directly produced by radiation-induced dispersion polymerization in aqueous alcohol media using poly(N-vinylpyrrolidone) as a steric stabilizer at room temperature. The hydrodynamic diameter of a polymer particle and its distribution were measured on a dynamic laser light-scattering spectrometer. This method takes advantages of the specialties of radiation induction, and highly uniform polymer microspheres were obtained with high conversion. The number of the particle produced in the early stage of the polymerization was found to be constant during the remainder of the polymerization. The effects of various polymerization parameters, such as absorbed dose rate, monomer concentration, stabilizer content, medium polarity, and polymerization temperature on the particle size and size distribution were systematically investigated.     

Emulsion polymerization of styrene using irreversible addition–fragmentation chain transfer agents: effect on the course of the polymerization and molecular weight

The emulsion polymerization of styrene with three different chain transfer agents (CTAs) based on irreversible addition–fragmentation chain transfer (AFCT) mechanism was first reported in this work. The influences of these irreversible AFCT agents on the rate of polymerization, particle size, and molecular weight were investigated. It was found that the intrinsic activity and desorption behaviors of the CTAs determined the efficiency for molecular weight control, rate of polymerization, and particle size in the emulsion polymerization. It has been demonstrated that the rate of polymerization and particle size decreased dramatically in the presence of the irreversible AFCT agents with high chain transfer constant (ethyl α-p-toluenesulfonyl-methacrylate), meanwhile, the molecular weight of the polystyrene could not be controlled well, whereas the irreversible AFCT agents with low chain transfer constant (butyl(2-phenylallyl)sulfane and 2,3-dichloropropene) had a slight effect on the polymerization rate, particle size, and were fairly well for molecular weight control over the whole conversion range in the emulsion polymerization of styrene. The average number of radicals per particle and the number-average molecular weight were calculated by classical radical emulsion polymerization theory, and the experimental results were in good agreement with the results of model calculations, when the irreversible AFCT agents were used as CTAs. The effect of chain transfer agents on the kinetics and nucleation in the emulsion polymerization of styrene can be attributed to desorption of chain-transferred radicals from the polymer particles. The results of this work show that butyl(2-phenylallyl)sulfane as CTA in emulsion polymerization of styrene provides the best balance between the rate of polymerization and the efficiency for molecular weight control conflicting tendencies.     

The effect of different catalytic chain transfer agents on particle nucleation and the course of the polymerization in ab initio batch emulsion polymerization of methyl methacrylate

The effect a Co(II) based catalytic chain transfer agent (CCTA) has on the course of the polymerization and the product properties of an emulsion polymerization is governed by the intrinsic activity and the partitioning behavior of the catalyst. The effect on the conversion time history, the molecular weight distribution and the particle size distribution is evaluated in batch emulsion polymerization of methyl methacrylate for three different CCTAs, which cover a range of intrinsic activities and partitioning behaviors. It was demonstrated that radical desorption from the particle phase to the aqueous phase preceded by chain transfer is the main kinetic event controlling the course of the polymerization and the product properties in terms of the particle size distribution. The experimental results show that the aqueous phase solubility of the CCTA is the key parameter controlling the course of the polymerization and the particle size distribution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1038–1048, 2010     

Influence of a reversible addition–fragmentation chain transfer agent in the dispersion polymerization of styrene

Dispersion polymerization was applied to the controlled/living free‐radical polymerization of styrene with a reversible addition–fragmentation chain transfer (RAFT) polymerization agent in the presence of poly(N‐vinylpyrrolidone) and 2,2′‐azobisisobutyronitrile in an ethanol medium. The effects of the polymerization temperature and the postaddition of RAFT on the polymerization kinetics, molecular weight, polydispersity index (PDI), particle size, and particle size distribution were investigated. The polymerization was strongly dependent on both the temperature and postaddition of RAFT, and typical living behavior was observed when a low PDI was obtained with a linearly increased molecular weight. The rate of polymerization, molecular weight, and PDI, as well as the final particle size, decreased with an increased amount of the RAFT agent in comparison with those of traditional dispersion polymerization. Thus, the results suggest that the RAFT agent plays an important role in the dispersion polymerization of styrene, not only reducing the PDI from 3.34 to 1.28 but also producing monodisperse polystyrene microspheres. This appears to be the first instance in which a living character has been demonstrated in a RAFT‐mediated dispersion polymerization of styrene while the colloidal stability is maintained in comparison with conventional dispersion polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 348–360, 2007     

Synthesis of monodisperse anionic submicron polystyrene particles by stabilizer-free dispersion polymerization in alcoholic media

In this work, monodisperse polystyrene (PS) particles were synthesized in ethanol/water medium using sodium salt of styrene sulfonic acid and 2,2′-azobis(isobutyronitrile) as ionic comonomer and nonionic initiator, respectively. The polymerization was carried out at low agitation speed, and no stabilizer (or surfactant) was added to the polymerization medium. This polymerization system (stabilizer-free dispersion polymerization) was initiated as a homogeneous solution of monomer, comonomer, medium, and initiator. With the production of free radicals, polymerization developed into a heterogeneous system. The effect of various polymerization conditions on the size and size distribution of the obtained particles was evaluated. The experimental results showed that with an increase in ethanol content, the size of the particles increased while no significant change was observed in particle size distribution. Furthermore, with increasing ionic comonomer content, the size of the particles decreased and their size distribution became broader. Moreover, it was observed that addition of an electrolyte to the polymerization medium also increased the particles’ size and broadened their size distribution. It is noteworthy to point out that the coagulation occurred in higher amounts of electrolyte. Finally, it is concluded that the polar component of Hansen solubility parameter of the polymerization medium affects the particle size and particle size distribution greatly.     

Kinetics and mechanism of emulsifier-free emulsion copolymerization: Styrene-methyl methacrylate-acrylic acid system

The emulsifier-free emulsion copolymerization of styrene (St) and methyl methacrylate (MMA) in the presence of functional monomer acrylic acid (AA) was carried out in batch process. The kinetics was investigated in detail using model function, Integrated Gamma Function. The morphology and size of particles were monitored continuously by TEM all along the polymerization. It was found that the nucleation, polymerization rate increase with increasing concentration of the functional monomer AA, initiator ammonium persulfate (APS), and polymerization temperature T, and APS plays a predominant role in the particle nucleation process. The particle nucleation stage ceased at about 10% conversion and the steady stage can be extended to about 70% conversion. The particle nucleation is likely to yield primary particle via the mechanism of homogeneous coagulative nucleation and coagulation of the primary particle to yield uniform particles. The particle growth in the postnucleation stage is via a shell growth mechanism. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2649–2656, 1999     

Simulation of secondary particle formation in seeded emulsion polymerization: The effect of surface charge density

Mathematical modeling and simulation were carried out to investigate the effects of the surface charge density of seed particles on secondary particle formation and the rate of polymerization in the early stage of emulsifier-free seeded emulsion polymerization of methyl methacrylate. Limited coagulation theory was applied to simulate new particle nucleation. The main factor influencing the capture rate of oligomeric radicals in a growing seed particle was assumed to be the electrostatic repulsion of seed particles. DLVO (Deryagiun-Landau-Verwey-Overbeek) theory was also introduced to estimate the electrical repulsion between seed particles and oligomeric radicals in the aqueous phase. In the case of highly charged seed particles, the adsorption rate of oligomeric radicals in the aqueous phase showed a strong effect on the polymerization rate. The low adsorption of oligomeric radicals results in a low value of the average number of radicals per particle. The surface charge density of seed particles was found to play an important role in limiting the polymerization rate at the beginning of the reaction and even in affecting the formation of secondary particles.     

RAFT种子乳液聚合反应初期的Monte Carlo模拟

自由基聚合是制备聚合物材料最为重要的技术 .但由于自由基极易进行双基终止 ,一般很难对其结构进行精确的控制 ,所得产物分子量宽 ,组成分布不易控制 ,很难制备嵌段共聚物 . 2 0世纪 90年代出现的活性自由基聚合技术 (RAFT)克服了上述缺点 ,成为高分子化学研究的热点[1] .RAFT聚合以其适用单体广、聚合条件温和以及活性高而成为最具前途的活性自由基聚合技术之一 .迄今为止 ,RAFT的研究大多集中在溶液和本体等均相聚合体系 [2～ 5] .乳液聚合有聚合速率快、环境友好、体系粘度低等优点 ,是活性自由基聚合工业化首选工艺 ,因而近年来活…     

聚合过程中原位生成助稳定剂的细乳液聚合

以甲基丙烯酸十二氟庚酯(DFMA)、甲基丙烯酸甲酯(MMA)、丙烯酸丁酯(BA)为共聚单体,不加任何传统的助稳定剂进行细乳液聚合.在共聚体系中,由于DFMA在初期反应生成的聚合物中占有较高比例,初期形成的少量低聚物可以起到助稳定剂作用,因此DFMA作为反应单体的同时,又可以原位生成助稳定剂,维持单体液滴或乳胶粒子的稳定,以细乳液聚合的方式进行聚合.分别采用油溶性引发剂(AIBN)和水溶性引发剂(KPS)引发聚合,考察细乳液聚合过程中乳胶粒子粒径的变化规律,粒径由初始时刻的400nm左右减少到80nm左右,最终与使用传统的助稳定剂得到的粒径相当.提出了原位生成助稳定剂的细乳液聚合机理,并使用交联剂验证了提出的原位生成助稳定剂的细乳液聚合机理.     

表面活性单体存在下的MMA／BA乳液共聚合（Ⅱ）：聚合动力？…

研究了表面活性单体「磺化－十二醇－烯丙基甘油－丁二酸酯钠盐（ＺＣ－Ｌ）」的用量对ＭＭＡ／ＢＡ／ＺＣ－Ｌ乳液聚合速率和粒径的影响,用Ｃｏｒｌｔｉｒ ＬＳ２３０型激光粒径分析仪测定聚合过程中乳液的粒径和粒径分布变化,并与ＭＭＡ／ＢＡ无皂乳液聚合及十二烷基苯磺酸钠存在下的ＭＭＡ／ＢＡ乳液聚合作了比较。「ＺＣ－Ｌ」〈ＣＭＣ时,成核机理为均相成核机理,乳胶粒需依靠粒子间的凝聚来提高表面电荷密度而稳定;「ＺＣ     

表面活性单体存在下的MMA/BA乳液共聚合(Ⅱ)聚合动力学及机理

研究了表面活性单体[磺化-十二醇-烯丙基甘油-丁二酸酯钠盐(ZC-L)]的用量对MMA/BA/ZC-L乳液聚合速率和粒径的影响,用CoulterLS230型激光粒径分析仪测定聚合过程中乳液的粒径和粒径分布变化,并与MMA/BA无皂乳液聚合及十二烷基苯磺酸钠存在下的MMA/BA乳液聚合作了比较.[ZC-L]CMC时,成核机理包括均相成核和胶束成核机理,生成的粒子因吸收体系中的表面活性单体而稳定存在.     

Emulsion polymerization of styrene in a single continuous stirred-tank reactor

The effects of mean residence time, initiation rate, and emulsifier concentration on particle formation, particle growth, and polymerization rate are examined for the emulsion polymerization of styrene in a completely mixed continuous stirred-tank reactor. Experimental measurements of number of particles, particle size distribution, polymerization rate, and molecular weights are compared with theoretical predictions. A theoretical model which incorporates Stockmayer's modification of the Smith-Ewart theory into the particle growth equation allows reasonably accurate prediction of polymerization rate, particle formation rate, and particle size distribution. Agreement between experimental measurements of number-average and weight-average molecular weights and a theory based on Smith-Ewart case 2 kinetics is also reasonable.     

AB2型聚合物流体的表面结构性质

在密度泛函理论(DFT)框架下, 应用改进的基本度量理论(MFMT)表达硬球作用对自由能泛函的贡献, 根据统计力学理论结合加权密度近似(WDA)表达聚合作用对自由能泛函的贡献, 建立了描述AB2型聚合物流体的化学势, 得到了聚合物流体在硬球颗粒表面的密度分布表达式, 计算了聚合物流体在硬球颗粒表面附近的密度分布, 并探讨了体积分数、聚合程度和硬球颗粒尺度对体系密度分布的影响. 此外, 通过体系密度分布, 进一步分析了体积分数、聚合程度和硬球颗粒尺度与剩余吸附的关系.     

Particle formation under monomer‐starved conditions in the semibatch emulsion polymerization of styrene. I. Experimental

Particle formation and particle growth compete in the course of an emulsion polymerization reaction. Any variation in the rate of particle growth, therefore, will result in an opposite effect on the rate of particle formation. The particle formation in a semibatch emulsion polymerization of styrene under monomer‐starved conditions was studied. The semibatch emulsion polymerization reactions were started by the monomer being fed at a low rate to a reaction vessel containing deionized water, an emulsifier, and an initiator. The number of polymer particles increased with a decreasing monomer feed rate. A much larger number of particles (within 1–2 orders of magnitude) than that generally expected from a conventional batch emulsion polymerization was obtained. The results showed a higher dependence of the number of polymer particles on the emulsifier and initiator concentrations compared with that for a batch emulsion polymerization. The size distribution of the particles was characterized by a positive skewness due to the declining rate of the growth of particles during the nucleation stage. A routine for monomer partitioning among the polymer phase, the aqueous phase, and micelles was developed. The results showed that particle formation most likely occurred under monomer‐starved conditions. A small average radical number was obtained because of the formation of a large number of polymer particles, so the kinetics of the system could be explained by a zero–one system. The particle size distribution of the latexes broadened with time as a result of stochastic broadening associated with zero–one systems. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3940–3952, 2001     

半连续乳液聚合

从聚合速率，粒径及粒径分布，粒子数，分子量及分子量分布，共聚物组成；胶乳稳定性及有面基团浓度，膜性能等方面介绍了半连续乳液聚合的特点，并阐述水溶性大单体对半连续乳液聚合及其产物性能的影响。     

Microemulsion polymerization of styrene

Initiation of polymerization in styrene oil-in-water microemulsions by water-soluble potassium persulfate of oil-soluble 2,2′-azobis-(2-methyl butyronitrile) at 70°C gave stable latexes which were bluish and less translucent than the original microemulsions. The effects of initiator concentration, polymerization temperature, and monomer concentration on the kinetics, particle size distributions, and molecular weight distributions were investigated. The kinetics of polymerization were measured by dilatometry. In all cases, the polymerization rate shows only two intervals, which increased to a maximum and then decreased. There was no apparent constant rate period and no gel effect. A longer nucleation period was found for polymerizations initiated by potassium persulfate as compared to 2,2′-azobis-(2-methyl butyronitrile). The small latex particle size (20–30 nm) and high polymer molecular weight (1–2 × 10⁶) implies that each latex particle consists of two or three polystyrene molecules. The maximum polymerization rate and number of particles varied with the 0.47 and 0.40 powers of potassium persulfate concentration, and the 0.39 and 0.38 powers of 2,2′-azobis-(2-methyl butyronitrile) concentration, respectively. This is consistent with the 0.4 power predicted by Smith–Ewart Case 2 kinetics. Microemulsion polymerizations of styrene–toluene mixtures at the same oil-water phase ratio gave lower polymerization rates and lower molecular weights, but the same latex particle size as with styrene alone. A mechanism is proposed, which comprised initiation and polymerization in the microemulsion droplets, by comparing the kinetics of microemulsion polymerization with conventional emulsion and miniemulsion polymerization systems.     

Polymeric microspheres by radiation copolymerization of acrolein and various monomers at low temperatures

The preparation of polymeric microspheres having aldehyde groups by radiation polymerization of acrolein solution containing various monomers at low temperatures was studied, in which the monomer solution was dispersed with polyvinyl alcohol in order to obtain monomeric microspheres and then irradiated. The particle size of the microspheres from acrolein — 2-hydroxyethyl methacrylate system varied with polymerization and dispersion condition, in which the particle size increase of the concentration of 2-hydroxy ethyl methacrylate and its particle size distribution was broadened. In acrolein — polyethyleneglycol dimethacrylate system, the effect of the molecular structure of monomers on the particle size was studied, and it was found that the particle size decreased with number of oxyethylene units in monomers.