Semibatch anionic ring‐opening polymerization of octamethylcyclotetrasiloxane in emulsions: effect of the amount of seed polymer particles

Semibatch anionic ring‐opening polymerization of octamethylcyclotetrasiloxane with the use of seed polymer particles in emulsions was studied. The concentration of the emulsifier was set above the critical micelle concentration. We investigated the effect of the amount of seed polymer particles on the chemical kinetics and the average particle size and distribution. During monomer starving conditions the polymerization rate strongly depended on the monomer feed rate and not on the amount of seed particles. Throughout the entire monomer feed period the average particle size increased. This increase depended on the number and the size of seed particles. In emulsions with higher particle sizes higher equilibrium conversions were obtained. In our opinion, a greater extent of backbiting reactions is responsible for lower equilibrium conversions during and at the end of the process. The seeded semibatch process seems a reasonable choice for designing emulsion products with high monomer conversion and desired particle size. © 2012 Society of Chemical Industry     

核壳结构聚硅氧烷/丙烯酸酯复合乳液(Ⅰ)乳化剂对乳液聚合过程及粒径分布和粒子形态的影响

采用种子乳液半连续法合成了具有高有机硅含量的聚硅氧烷/丙烯酸酯核壳结构复合乳液,研究乳化剂的种类、复配比例及质量浓度对有机硅／丙烯酸酯壳核乳液性能与乳胶粒径、分布和结构的影响.结果表明：阴离子乳化剂十二烷基硫酸钠(SDS)、十二烷基磺酸钠(SDS-2)、十二烷基苯磺酸钠(SDBS)所合成的乳胶粒子粒径依次增大,SDS与非离子型乳化剂OP-10复配使用时,随OP-10质量分数的增加,聚合速率和转化率降低,化学稳定性增加,乳胶粒子粒径增大,分布变宽,确定了复合乳化剂的最佳配比.随复合乳化剂浓度的增加,聚合速率加快、转化率增加,乳胶粒子粒径减小而分布加宽.通过改变乳化剂加入方式可减小乳胶粒子的粒径分布.为减少壳层聚合物新粒子的产生,需严格控制乳化剂的浓度,使加入的壳层单体处于“饥饿”状态,在乳胶粒子表面富集、引发聚合,形成表层“过渡层”,最终形成核壳结构复合粒子.     

Semibatch anionic ring-opening polymerization of octamethylcyclotetrasiloxane in emulsion

The semibatch anionic ring-opening polymerization of octamethylcyclotetrasiloxane in emulsion was studied under the condition of no seed particles used in polymerization system. Concentration of emulsifier was set above critical micelle concentration. Effect of monomer feed rate on the chemical kinetics, average particle size and distribution and on the polymer molar mass and distribution was investigated. During monomer addition, polymerization rate was constant and controlled by the monomer feed rate. According to the proposed mechanism for anionic polymerization in emulsion, it was assumed that also the number of active polymerization sites and monomer concentration at the particle surface, where propagation occurs, remain constant. A continuous increase of average particle size and absence of extensive condensation reactions at high conversion suggested that the freshly added monomer diffuses toward hydrophobic polymer particles, where it is consumed in propagation reaction and/or accumulated in the particle core.     

Effect of stirring on the emulsion polymerization of styrene

The purpose of this paper is to clarify the effect of stirring on the course of emulsion polymerization of, for example, styrene. It establishes the existence of an optimum range of stirring speed and three important factors which must be considered in carrying out emulsion polymerization. (1) Stirring significantly affects the course of reaction in the presence of an imperfectly purified nitrogen atmosphere. Consequently, the number of polymer particles produced and the polymerization rate per particle will be affected. (2) At higher stirring speeds, polymer particles coagulate and coalesce. At lower stirring speeds, the reaction rate is controlled by the monomer transport rate from monomer droplets to the aqueous phase. (3) Stirring contributes to the reduction of the number of micelles because emulsifier molecules are adsorbed onto the surfaces of monomer droplets finely dispersed by the stirring. At low emulsifier concentrations near the critical micelle concentration, this effect cannot be neglected.     

Semibatch emulsion polymerization of butyl acrylate. II. Effects of emulsifier distribution

The effects of emulsifier distribution ratio between the initial charge and the feed on particle formation and kinetics of butyl acrylate emulsion polymerization, using sodium lauryl sulfate as emulsifier and potassium persulfate as initiator, were investigated. The number of particles increased with initial emulsifier concentration in the reactor charge. It was shown that traditional ranking, in terms of number of particles produced, of semibatch emulsion polymerization with monomer emulsion feed is not always justified and a semibatch emulsion polymerization can produce far more particles than a conventional batch emulsion polymerization. The number of polymer particles was found to be practically independent of the emulsifier distribution ratio between the charge and the feed for a high overall emulsifier concentration, while for a low overall emulsifier concentration, the number of particles increased with initial loading of the emulsifier. The polydispersity index (PDI) of the final latexes showed a minimum with emulsifier distribution. A bimodal particle size distribution, and a latex with a large PDI, was obtained when there was no emulsifier in the charge. As the initial emulsifier charge increased, a unimodal PSD with a smaller PDI was obtained. With higher proportions of emulsifier in the initial charge, the PDI rose again due to particle nucleation at monomer‐starved conditions, and a skewed unimodal PSD was obtained. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 582–597, 2001     

高固含量苯丙微乳液聚合的研究

以阴／非离子型乳化剂作为复合乳化剂体系，进行高固含量St-BA微乳液聚合的研究。获得了固含量达34％，而乳化剂总用量为3．0％、乳液粒径为38．2nm的聚合物微乳液。讨论了聚合方法、乳化剂、反应温度、单体滴加速度、搅拌速率等因素对微乳液聚合的影响。     

Winsor I-like (micro)emulsion polymerization of styrene initiated by oil-soluble initiator

Batch emulsion polymerization of styrene initiated by an oil-soluble initiator and stabilized by non-ionic emulsifier (Tween 20) has been investigated. The rate of polymerization vs. conversion curve shows the two non-stationary rate intervals typical for the non-stationary-state polymerization. This behavior is a result of the continuous particle nucleation and the decrease of monomer concentration at the reaction loci with increasing conversion. The initial increase of the polymerization rate is attributed to the increase of particle number and the polymerization proceeding under the monomer-saturated condition—the Winsor I-like (micro)emulsion polymerization. The decrease of the polymerization rate is the result of the depressed transfer of monomer from the monomer reservoir to the reaction loci. Above 50 °C the monomer emulsion separates into two phases: the upper transparent monomer phase and the lower blue colored (microemulsion) phase. The polymerization mixture consists of the microdroplets (act as the reaction loci) and large degradable monomer droplets (act as the reservoir monomer and emulsifier). The continuous release of emulsifier from the monomer phase and the microdroplets induce the continuous particle nucleation up to high conversion. The initial formation of large particles results from the agglomeration of unstable growing particles and monomer droplets. The size of large (highly monomer-swollen) particles decreases with conversion and they merge with the growing particles at ca. 40-50% conversion. The coarse initial emulsion transformed during polymerization to the fine (semitransparent) polymer emulsion as a result of the continuous particle nucleation, the shrinking of highly monomer-swollen polymer particles and the depletion of monomer droplets. The low overall activation energy of polymerization is mainly ascribed to the decreased barrier for entering radicals into the latex particles with increasing temperature.     

Microemulsion polymerization of styrene in the presence of macroinimer

The kinetics of o/w electrostatically and sterically-stabilized microemulsion polymerization of styrene with and without macromonomeric azoinitiator (macroinimer; MIM) have been investigated. The microemulsion polymerization stabilized by the ionic emulsifier sodium dodecyl sulfate (SDS) or the non-ionic emulsifier Tween 20 (Tw 20) was initiated by ammonium peroxodisulfate (APS)/sodium thiosulfate (STS) redox system. The rate of polymerization vs. conversion curve shows the two non-stationary rate intervals. This behavior is a result of two opposing effects, the continuous particle nucleation and the decrease of monomer concentration at the reaction loci. The addition of MIM favors the additional particle nucleation. The sterically (Tw 20)-stabilized microemulsion polymerization is much faster than that of the electrostatically (SDS)-stabilized microemulsion polymerization. This was attributed to the higher Tw 20 concentration and increased solubilization of MIM and comonomer concentration in the polymer particles. The formation of initial large polymer particles is attributed to the intensive agglomeration polymer particles with monomer droplets. The continuous decrease in the average size is mainly attributed to the additional particle nucleation.     

Particle nucleation mechanism for the emulsion polymerization of styrene with a novel polyester emulsifier

The particle nucleation mechanism in emulsion polymerization of styrene with a novel polyester emulsifier, 5‐sulfoisophthalic acid dimethyl ester sodium salt‐modified tetracarboxylic acid‐terminated polyester (SMTAPE), was investigated. The consumption of SMTAPE micelles was monitored by the measurement of surface tension during the emulsion polymerization. Kinetic studies and emulsifier consumption clearly showed that a continuous nucleation mechanism without Smith–Ewart interval II was characteristic of this system. It was attributed to the high concentration of SMTAPE emulsifier in the polymerization, which led to a large surface area and a vast number of micelles around 10 nm in size that served as the major locus of particle nucleation. A broad particle size distribution was observed throughout the reaction, and the nucleation period lasted well into the reaction until the disappearance of the micelles or the disappearance of monomer droplets. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1061–1070, 2001     

Modeling the emulsion polymerization of amino-functionalized latex particles

A mathematical model for a semicontinuous seeded cationic emulsion polymerization was developed. The model includes the most distinctive features of the copolymerization of a cationic hydrophilic monomer with a hydrophobic one, including polymerization of the hydrophilic monomer in the outer shell of polymer particles and in the aqueous phase, and the possibility of having radical concentration profiles in the polymer particles.The reactions were carried out by means of a semicontinuous seeded cationic emulsion polymerization under starved conditions for styrene, which was the main monomer employed.The model predicts the evolution of the fractional overall conversions, the thickness of the outer shell, the total surface charge density and the partial conversions for the semicontinuous seeded cationic emulsion polymerization of styrene and aminoethyl methacrylate hydrochloride. Furthermore, the model can distinguish between the surface charge density provided by the cationic monomer than that given by the cationic initiator. Therefore, this model can predict the best conditions to obtain well-defined latexes with specific amounts of surface amino and amidine groups useful for immunoassays.     

反相乳液聚合合成聚丙烯酰胺

以甲苯为介质,Span80/Span20为乳化剂,叔丁基过氧化氢/亚硫酸氢钠氧化还原体系为引发剂,采用反相乳液聚合制备了分子量高达9.4×106的聚丙烯酰胺乳液。研究了乳化剂种类及用量、引发剂种类及用量、油水比、单体浓度,反应温度对共聚物相对分子量、聚合转化率以及聚合反应速率的影响。其最佳聚合配方及工艺条件为:油水体积比为1.4,单体浓度30%,引发剂用量0.003%,乳化剂用量12%,聚合温度30℃。     

高固体分无凝胶丙烯酸酯乳液合成工艺探讨

为制备高固体分无凝胶丙烯酸酯乳液,探讨了聚合方法,单体和引发剂的加料方式,乳化剂用量和种类,以及保护胶体种类对丙烯酸酯乳液性能的影响。结果表明：全部预乳化效果最佳,4h内无凝胶产生;半连续滴加较一次性或分批加入更有利于乳液体系稳定;采用阴离子与非离子乳化剂复配及加入保护胶体有利于提高聚合体系的固含量。筛选出最佳的制备工艺条件：采用全部预乳化、半连续种子乳液聚合;以十二烷基硫酸钠（SDS）与烷基酚聚氧乙烯醚（OP-10）为复合乳化剂（质量比为1：1）,其用量为3％;保护胶体量为0．8％;引发剂量为0.3％;反应温度为78℃;反应时间为4h;搅拌速率为400r／min。此条件下可合成固含量达60．03％的带蓝光乳白色丙烯酸酯乳液。     

乳液聚合成核阶段的模拟与分析

建立了乳液聚合成核阶段的Monte Carlo模型，并用计算机对一个体积为10^-17m^3的微型反应器中苯乙烯的乳液聚合进行了模拟。以计算机生成随机数作为自由基被胶束和乳胶粒捕获的几率，模拟了在微型反应器中每一个自由基的生成、被胶束或乳胶粒捕获的过程以及每一个乳胶粒的生成及增长过程。通过对每一个乳胶粒在增长过程中各参数的统计计算，研究了乳液聚合成核阶段诸参数(乳胶粒数目、乳胶粒直径与粒径分布、单体转化率、聚合反应速率等)与乳化剂浓度[S]及引发剂浓度[I]的关系。结果表明，苯乙烯的乳液聚合体系中乳胶粒数目与[S]^0.5996[I]^0.4016成正比：在成核阶段乳胶粒直径分布先变宽后变窄，乳液聚合过程中乳胶粒直径分布有自动变窄的趋势；成核阶段持续时间t12与[S]^0.60[I]^0.60成正比，成核阶段结束时的单体转化率X12与[S]^1.20[I]^0.20成正比。     

常规乳液聚合下提高(甲基)丙烯酸高碳醇酯转化率的途径

以丙烯酸十八酯、甲基丙烯酸甲酯为共聚单体,反应型乳化剂MIXSTAR 6550和非反应型非离子乳化剂NOVELUTION 390复配作为复合乳化剂,过硫酸铵为引发剂,研究了乳化剂用量、3种质子[H ⁺]及[H ⁺]浓度对聚合稳定性、丙烯酸十八酯共聚活性及总单体转化率的影响。结果表明:反应型乳化剂MIXSTAR 6550具有将强憎水的丙烯酸高碳醇酯摆渡到乳胶粒或增溶胶束中的能力,同时强的质子[H ⁺]降低了丙烯酸高碳醇酯的活化能,使丙烯酸高碳醇酯在常规乳液聚合条件下可与其他丙烯酸酯共聚。即使丙烯酸高碳醇酯引入量为45%,总单体转化率也可达97%以上,实现了(甲基)丙烯酸高碳醇酯在常规乳液聚合下可与其他单体进行理想共聚的目的。     

Study of different types of monomer emulsion feedings to semibatch emulsion polymerization reactors

Semibatch emulsion polymerization processes with a monomer emulsion feed are of great importance in both academia and industry. Monomer emulsion feeds can be applied to semibatch reactors using either a stream of an emulsified monomer or two streams of a neat monomer feed and an aqueous solution of an emulsifier. The effect of the feeding policy on the rate of polymerization and on the secondary particle formation was studied for a seeded semibatch emulsion polymerization of styrene. When a single-stream monomer emulsion feed is applied to a semibatch process, the monomer-swollen micelles formed in the feed might become the locus of initiation upon entering the reaction vessel. Under the conditions of this study, the application of monomer emulsion feed in either one stream or two streams did not result in secondary particle formation. The incoming monomer-swollen micelles were disintegrated to supply emulsifier molecules for the stability of growing particles, before they can capture radicals and become polymer particles. The rate of polymerization was found to be independent of the way that the monomer emulsion feed is added. In the absence of nitrogen, the rate of polymerization decreased more appreciably for the monomer emulsion feed, due to the oxygen dissolved in the emulsified monomer. The number of particles, however, was not affected by the purging policy. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2472–2477, 2001     

Kinetics of emulsifier adsorption and nucleation of latex particles

Evidence suggesting that the ultimate latex particles formed in the emulsion polymerisation of styrene are formed by the coalescence of unstable primary particles appears incompatible with the usual assumption that latex particles are predominantly nucleated from monomer-swollen micelles in this system. However, this is not necessarily the case if the rate of emulsifier adsorption is not always sufficient to maintain a saturated monolayer of adsorbed emulsifier at the surface of growing latex particles so long as emulsifier micelles remain in the system. This appears to be the situation particularly when non-ionic emulsifiers are used. Even with ionic emulsifiers abnormally high emulsifier/monomer ratios are needed to prevent the coalescence of primary latex particles. Some very high molecular weight polymer (controlled by the transfer constant to monomer) would be expected in the initial stage of styrene emulsion polymerisation if the micellar nucleation of latex particles is dominant.     

Experimental study of emulsion polymerization with crosslinking

Herein is reported the results of an extensive experimental investigation of the kinetics of emulsion polymerization as affected by crosslinking in the polymer particles. The model monomer system, methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA), was chosen for this study due to its earlier comprehensive investigation in bulk polymerization. Standard recipes with sodium dodecylsulfate (SDS) as anionic emulsifier and potassium persulfate (KPS) as initiator were used for the batch emulsion polymerizations. Results, which clearly show the effect of crosslinking on the kinetics, are discussed in detail. These include swellability of polymer particles by monomer; polymer particle nucleation rates, below and above the critical micelle concentration (CMC); average number of radicals per particle; and gel-sol levels. It was found advantageous to use electron spin resonance (ESR) to follow radical concentrations during crosslinking in polymer particles. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 935–957, 1997     

核壳结构苯丙乳液上光油的研制

采用预乳化工艺及半连续种子聚合法,通过St-BA-MMA-AA四元共聚反应,制得了具有核壳结构的苯丙乳液。讨论了乳胶粒子大小及形态对MFT的影响,并研究了乳化剂用量、阴／非离子乳化剂配比、核壳两阶段乳化剂配比及功能性单体的用量及加入方式对乳液性能的影响。     

Hybrid emulsifiers enhancing polymerization stabilities and properties of pressure sensitive adhesives

In this study, a series of (anionic and nonionic) emulsifiers were investigated to prepare acrylic pressure sensitive adhesives (PSA) with core‐shell structure by semicontinuous emulsion polymerization. The cloud point of different emulsifiers was characterized to explain the emulsifier effects on the emulsification ability. It was interestingly found that the hybrid emulsifiers (anionic coupling with nonionic) with optimized compositions could enhance the stability of emulsion system and improve the properties of PSA compared with the mono‐emulsifier. The stability of emulsion polymerization, the appearance of the emulsion system and the properties of PSA were studied in details by changing the proportion and the content of hybrid emulsifiers. When the ratio of sodium dodecyl sulfate (SDS: anionic emulsifier) to polyoxyethylene alkyl phenyl ether (OP‐10: nonionic emulsifier) reached 2 : 1, the content of hybrid emulsifiers reached 3 wt % and the reaction temperature was around 80°C, a better emulsion system was obtained in terms of comprehensive properties. At this condition, the synthesized PSA demonstrated the good holding power and 180° peel strength properties with fair tacky property, which was promising for industrial applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

阳离子聚合物乳液的合成研究

本文通过常规乳液聚合法合成阳离了聚合物乳液，讨论了反应引发剂、阳离子乳化剂、功能性单体、共聚单体和单体浓度等各种因素对聚合速率、乳液性能等的影响。