A kinetic investigation of thermally initiated emulsion copolymerization of styrene and methylmethacrylate without conventional initiators

The thermally initiated emulsion copolymerization of styrene (ST) and methyl methacrylate (MMA) was carried out in the absence of conventional initiators. The hydroperoxide (HPO) concentration in the monomers, sodium dodecyl sulfate (SDS), deionized water, and the formulation of those for emulsion copolymerization were measured. The HPO concentration in ST and MMA increased with the storage time, and were considered to be the major sources of HPO. The thermal decomposition of hydroperoxide in monomers, the thermal initiation of ST by Mayo mechanism, and the complex formation between SDS and the monomers were proposed to be three main sources of the radical generation. It was confirmed that new polymer particles were generated throughout the polymerization process, and consequently resulted in a broader distribution of polymer particle size, compared with that for conventional emulsion polymerization. Approximately 80 wt % of monomer conversion was obtained in the presence of SDS at 373 K in 24 h. The initiation rate of the 30 wt % monomer charge was faster than those of 10 wt % and 20 wt % monomer charge. The latex instability at higher solid content was improved by adding electrolyte to promote the electrostatic repulsion force between the polymer particles. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 455–467, 2002; DOI 10.1002/app.2343     

Iron (II) chloride catalyzed emulsion polymerization of methyl methacrylate using different initiators

The emulsifier and emulsifier-free emulsion polymerization of methyl methacrylate (MMA) using sodium bisulphite, acetaldehyde sodium bisulphite (ACSB), octyladehyde sodium bisulphite (OSB), benzaldehyde sodium bisulphite (BSB), and acetone sodium bisulphite (ASB) as different initiators, and dodecyl benzene sodium sulphonate (DBSS) as an emulsifier, were carried out at 30, 40, and 50°C. The effect of iron (II) chloride on the rate of polymerization and on the viscosity-average molecular weight was investigated. The effect of temperature, iron (II) chloride, and the type of initiator on the tacticity of the obtained polymers was investigated by means of nuclear magnetic resonance (NMR) spectroscopy. The effect of iron (II) chloride and the four carbonyl adducts (ACSB, OSB, BSB, and ASB) on the volume-average diameter and the number of polymer particles per unit volume was investigated. It was found that iron (II) chloride has a pronounced catalytic effect on the emulsion polymerization. The initiating powers of the four carbonyl adducts, ACSB, BSB, OSB, and ASB, were found to be 3.27, 0.6, 1.78, and 0.23, respectively. The rate of emulsion polymerization and viscosity-average molecular weight were found to be dependent on the emulsifier concentration, initiator type and concentration, temperature, and amount of the catalyst (FeCl₂). © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1725–1738, 1998     

Ultrasound‐assisted emulsion polymerization of methyl methacrylate and styrene

In this article, we report on the effect of using ultrasound during emulsion polymerization. This work differs somewhat from that previously reported in that ultrasound is used in conjunction with conventional initiators. The aim is to observe the changes in the nature of polymerization and the synthesized polymer. In this work, reaction conditions and compositions typical of conventional emulsion polymerization are used. Azo‐bisisobutyronitrile and potassium per sulfate are the initiators used. The initial indication is that the rate of polymerization and the final conversion are higher when ultrasound is introduced into the polymerization system. This effect is more pronounced at lower temperatures (50°C) and low initiator concentrations (0.01%). At higher temperatures (70°C) the polymerization rate is seemingly unaffected by the use of ultrasound. The final product in all the experiments is a latex. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 101–104, 2000     

Morphological characterization of attapulgite/poly(methyl methacrylate) particles prepared by soapless emulsion polymerization

BACKGROUND: The synthesis of core–shell inorganic/polymer nanocomposites, in which the polymer shell determines the chemical properties and the interaction with the environment, whereas their physical properties are governed by both the size and shape of the inorganic core and the surrounding organic layer, is an area of increasing research activity. RESULTS: Core–shell and bead–string shaped attapulgite/poly(methyl methacrylate) (ATP/PMMA) nanocomposite particles were prepared by soapless emulsion polymerization in an aqueous suspension of attapulgite organically modified with cetyltrimethylammonium bromide. CONCLUSION: Transmission electron microscopy analysis results showed that the amounts of the monomer added had no influence on the morphologies of the ATP/PMMA particles. The morphologies only depended on the length/diameter ratio of the attapulgite fibrillar single crystal used. Long ATP needles formed the bead–string structure while short ATP needles formed the core–shell structure. Copyright © 2007 Society of Chemical Industry     

Encapsulation of TiO2 by emulsion polymerization with methyl metacrylate (MMA)

Summary This paper presents a methodology of encapsulation of TiO₂ (Titanium dioxide) by emulsion polymerization on the proposal to modify the physical-chemical properties of the pigment surface. In the proposed methodology the TiO₂ was previously modified by isopropoxy-titanium-tri-isostearate, before being encapsulated by emulsion polymerization using Methyl Methacrylate as monomer. The effects of the polymerization process, type of initiator and monomer concentration in the efficiency of encapsulation were studied. The encapsulated pigment was characterized by Thermogravimetric Analysis (TGA), Light Scattering (LS) and Transmission Electron Microscopy (TEM).     

Different composition poly(methyl methacrylate-co-butyl methacrylate) copolymers through seeded semi-batch emulsion polymerization

In the present work the synthesis and the chemical and thermal characterization of poly(methyl methacrylate-co-butyl methacrylate) copolymer, in three different macromolecular compositions, are reported. The aim of the present work was the identification of a standard method to obtain copolymers with controlled macromolecular composition, molecular weights and particle size distribution, together with the identification of the effect of the macromolecular composition on the material properties. A monomer-starved seeded semi-batch emulsion reaction was carried out and optimized, monitoring the kinetic of the copolymerization through the evaluation of residual monomer amounts. Then, an evaluation of the macromolecular composition was performed by Fourier transform infrared spectroscopy analysis. Molecular weight, molecular weight distribution, latex characteristics and thermal behaviour were also investigated.     

氧化还原体系引发苯乙烯乳液聚合

以不同的过氧化物引发剂分别与硫酸亚铁组成氧化还原引发体系,引发苯乙烯的乳液聚合,研究反应温度和还原剂用量等对聚合的影响.采用气相色谱、三检测体积排除色谱、动态光散射对单体转化率、聚苯乙烯的相对分子质量及其分布和乳胶粒径进行了分析.结果表明:升高温度或增加还原剂用量均会使聚合物的相对分子质量增大,聚合反应速率加快,与常规...     

聚乙二醇存在下苯乙烯/甲基丙烯酸甲酯无皂乳液聚合体系的动态表面张力

利用最大泡压法（MBPM）研究了苯乙烯（St）/甲基丙烯酸甲酯（MMA）在有、无聚乙二醇（PEG）水溶液中进行无皂乳液聚合过程中的动态表面张力变化。发现PEG使体系反应速率变慢,反应50 min,有PEG参与的体系转化率只有49%,而无PEG参与的体系转化率已达到98%以上,接近终点。St/MMA和引发剂形成的聚合物在PEG的作用下,形成了一种具有更强表面活性的聚合物,表面活性水平高于PEG以及无PEG参与聚合体系的聚合物,但弱于混合单体及齐聚物。这种较强表面活性的聚合物在转化率只有5%的时候就已经存在,是聚合物进入粒子堆形成稳定小粒子的动力,并最终使粒子带有足够脱离粒子堆的表面电荷。     

AC对St或MMA为壳层单体种子乳液聚合的影响

在种子乳液聚合中加入发泡剂偶氮二甲酰胺(AC),制备了可发气核壳结构复合微球。探讨了AC用量对以聚苯乙烯(PSt)微凝胶为种子,St或甲基丙烯酸甲酯(MMA)为壳层单体的2种体系稳定性及转化率和反应速率的影响。结果表明,以MMA为壳层单体的聚合体系是较理想体系。当AC用量从1g增加到8g时,以St为壳层单体体系的最终转化率从96．2％下降到74．2％,以MMA为壳层单体体系的最终转化率基本不变,保持在96％左右。但AC的加入使以MMA为壳层单体体系的反应速度最大值的出现时间推后了10min,且其值仅为未加入AC体系的1／2左右。     

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     

氧化还原引发聚合丙烯酸酯乳液及胶粘剂的研究

主要探讨了氧化还原引发剂用量对聚合反应速度、单体转化率的影响。同时对乳化剂用量,湿润剂种类用量,增粘乳液对乳液胶粘剂的性能的影响也进行了分析。研究发现:适宜的氧化还原引发体系的用量在单体的0．3％-0．8％之间;复合乳化剂用量为总量的2％-4％之间;LSR-101湿润剂为单体总量的0．5％-1．7％;增粘乳液用星为25％时,可得到转化率高,粘接性能良好的胶粘剂。     

Factorial experimental design approach in semicontinuous emulsion polymerization of methyl methacrylate to study the effect of process variables

This article describes the effect of various process variables in the semicontinuous emulsion polymerization of methyl methacrylate. A series of poly(methyl methacrylate) (PMMA) emulsions were prepared using ammonium persulphate as initiator in absence and presence of Dowfax 2AI as surfactant. The effect of process variables such as initiator concentration, monomer concentration (solid content), surfactant concentration, reaction temperature, monomer feeding time, and holding time were systematically studied on monomer conversion, particle size, gel content, and molecular weight using a two‐level fractional factorial experimental method. Analysis of fractional factorial design revealed that surfactant concentration, monomer concentration, initiator concentration, and monomer feeding time affect all the properties. However, the surfactant concentration and the interaction effect of initiator and monomer feeding time are the key variables influencing the properties of PMMA latex. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Emulsification in batch emulsion polymerization

Dispersion of liquid–liquid systems is often applied in industrial processes such as extraction, suspension, and emulsion polymerization. The influence of emulsification of the monomer in the aqueous phase on the course and outcome of the batch emulsion polymerization of styrene has been studied. A visual criterion was applied for determining the lowest impeller speed for sufficient emulsification (N*). It appeared that in polymerization experiments under the same conditions, N* was the critical value above which no further increase in polymerization rate was observed. Using a turbine impeller instead of a pitched blade impeller as well as using a larger impeller diameter provides better emulsification at constant power input. The results indicate that scale‐up with constant impeller tip speed is most appropriate in case of a turbine impeller. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3225–3241, 1999     

原子转移自由基法合成乙丙橡胶接枝物中的热聚合研究

采用原子转移自由基聚合法(ATRP)合成了三元乙丙橡胶与苯乙烯的接枝共聚物(EPDM-g-St),动力学研究表明聚合过程为“活性”聚合。在接枝聚合过程中发现了明显的苯乙烯热聚合现象。对接枝聚合中得到的均聚苯乙烯进行表征的结果表明,苯乙烯在ATRP接枝体系中的热聚合过程在一定程度上受到ATRP机理的控制;升高温度和延长反应时间使得热聚合更为显著。     

Morphology and thermodynamic analysis of composite polymer particles prepared by soap‐free emulsion polymerization in the presence of poly(methyl methacrylate) and polystyrene as biseeds

Biseeds emulsion polymerization was investigated with poly(methyl methacrylate) (PMMA) and polystyrene (PSt) as biseeds and styrene (St) as second‐stage monomer, as well as with thermodynamic analysis; namely, the principle of minimum interfacial free‐energy change was utilized to explain the competitiveness of different seeds for second‐stage monomer and the final equilibrium morphology of composite polymer particles. The experimental results indicated the polymeric particles prepared had bimodal size distribution and the PMMA seed particles showed a higher chance of obtaining St than that of the PSt seed particles, which was in agreement with the computational outcome by the principle of minimum interfacial free‐energy change. Owing to the kinetic factors, the equilibrium morphology could not be reached in the experiments. However, the results demonstrated that double or multiple seeds emulsion polymerization could be used as a model experiment to study the morphology of polymer particle and the morphological prediction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2675–2680, 2004     

Tl(III) initiated polymerization of methyl methacrylate in micellar phase

The polymerization kinetics of methyl methacrylate (MMA) was studied, using Tl(III)‐cyclohexanone (CH) redox system as initiator, in the presence of emulsifier [i.e., sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and thallium triacetate (TX‐100)] over a temperature range of 25–45°C. The effect of various concentrations of MMA, Tl(III), cyclohexanone, H⁺, and varying ionic strengths on the rate of polymerization, rate of Tl(III) consumption (?R_Tl), and the percentage of monomer conversion were examined in the presence of 0.015M SDS. The kinetic results of polymerization in the absence and presence of 0.015M SDS were compared in terms of overall activation energy (E_a) for the process. The viscosity‐average molecular weight (M_V) of the polymers, obtained in the presence of varying concentrations of anionic surfactant (SDS), was also determined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2480–2485, 2004     

N-对甲苯基马来酰亚胺乳液共聚物性能表征

通过乳液聚合制得N-对甲苯基马来酰亚胺(NPTMI)、甲基丙烯酸甲酯、苯乙烯的三元共聚物．采用热重分析、维卡软化点测试、差示扫描量热分析等方法研究了不同单体配比共聚物的热性能及力学性能．用凝胶渗透色谱(GPC)测定了共聚物的分子量及其分布。结果表明：加入NPTMI可以有效地提高共聚物的热稳定性,NPTMI质量分数为20％的共聚物与不含NPTMI的共聚物相比．玻璃化转变温度、维卡软化点、热分解起始温度、分解50％时的温度分别提高了22．6,19．5,42．8,46．2℃．但力学性能有所下降。GPC测定结果表明,分子量在合适的单体配比下出现最大值。     

Anionic polymerization of methyl methacrylate initiated by thiophenol

Methyl methacrylate (MMA) was polymerized by thiophenol without oxidants. Hydroquinone had no effect on the polymerization, indicating that the polymerization proceeded via a non-radical process. Since other monomers with an x,β-unsaturated carbonyl group polymerized similarly, the initiation and propagation were explained by the Michael addition. Radical scavengers such as 1,1-diphenyl-2-picrylhydrazyl(DPPH) and galvinoxyl enhanced the polymerization because of an accompanying radical polymerization initiated by radical species formed by the reaction of them with thiophenol. Aluminium acetylacetonate, which has no effect on radical polymerization, accelerated the thiophenol-initiated polymerization supporting the postulated mechanism.     

Shell growth mechanism in emulsifier-free emulsion polymerization: Morphological and kinetic studies

For systems of emulsifier-free emulsion polymerization having particle diameter (D_p) greater than 0.15–0.2μm, a shell-growth mechanism for particle growth was proposed. According to the mechanism, the polymeric radicals can propagate only within the shell region having a thickness about equal to the most probable end-to-end distance of the terminated polymer. This mechanism was considered to result from anchoring of hydrophilic ends of the growing radicals on the particle surface and from a high average number of radicals per particle. The occurrence of limiting conversion for such large particles was attributed to the consequence of shell-region polymerization characteristic of large emulsion particles and a monomer-diffusion-controlled polymerization mechanism within the particles during the high conversion period.