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     

Kinetic investigations of acrylic–polyurethane composite latex

The effect of various reaction parameters on the rate of polymerization, R_p, and on the particle size and morphology of aqueous acrylic–polyurethane hybrid dispersions, prepared by semibatch emulsion polymerization, was investigated. The particles of polyurethane dispersion were used as seeds during the polymerization of acrylic component: methyl methacrylate (MMA), butyl acrylate (BA), and a mixture of MMA and BA with the ratio of 1:1. These emulsions were found to form structured polymer particles in aqueous media using scanning electron microscopy. The kinetics of the emulsion polymerization was studied on the basis of Wessling's model. The influence of emulsifier and initiator concentrations, including the monomer feed rates, R_m, on the rates of polymerization and on the properties of the resulting dispersions were studied. The number of particles and the particle size were also measured during the polymerization process. The final values were found to be independent of the concentration of the emulsifier, initiator and the monomer feed rate in monomer starved conditions. In the steady‐state conditions, during the seeded semibatch hybrid emulsion polymerization, the rate of polymerization and the monomer feed rate followed the Wessling relationship 1/R_p = 1/K + 1/R_m. The dispersions MMA/PU, BA/PU, and MMA/BA/PU have K values of 0.0441, 0.0419 and 0.0436 mol/min, respectively. The seeded BA/PU hybrid polymerization proceeded according to Smith‐Ewart Case I kinetics, while the MMA/PU hybrid emulsions demonstrate Case II of the Smith‐Ewart kinetic model. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2639–2649, 2002     

Polystyrene latex particles bearing primary amine groups via soap‐free emulsion polymerization

Polystyrene latexes were prepared in the presence of an amino‐containing functional comonomer, N‐(3‐aminopropyl)methacrylamide hydrochloride (APMH), via soap‐free batch emulsion polymerization initiated by the cationic initiator 2,2′‐azobis(2‐amidinopropane) dihydrochloride. These latexes were characterized by studying the influence of the ionic comonomers on the polymerization kinetics, particle size, surface charge density and colloidal properties. The synthesized latexes were monodisperse with a final size between 100 and 600 nm depending on the APMH concentration. The initial polymerization rate and the particle number increased in accordance with the Smith–Ewart theory for soap‐free styrene emulsion polymerization with a hydrophilic functional comonomer. The final functionalization rate of the particles has been particularly studied with the intention of fitting the prepared latexes to be used in the immobilization of biological molecules for biological sample preparation and diagnostic applications. © 2020 Society of Chemical Industry     

Rate coefficient for radical desorption in emulsion polymerization

Investigators have proposed the rate coefficient for radical desorption from polymer particles to explain the kinetic deviation of the emulsion polymerization of water-soluble monomers such as vinyl acetate and vinyl chloride from the classical Smith and Ewart theory.⁶ In this article, the rate coefficient for radical desorption is theoretically derived by a different approach, and its applicability to vinyl acetate and vinyl chloride emulsion polymerization is examined in detail using experimental data available in the literature. The theory developed here predicts the average number of radicals per polymer particle in the emulsion polymerization of vinyl acetate and vinyl chloride.     

Elucidation of the miniemulsion stabilization mechanism and polymerization kinetics

Styrene/hexadecane miniemulsions were polymerized at 50°C using a redox initiator. The miniemulsions and their corresponding latexes were characterized in terms of size, polymerization rate, and surface properties. The resulting data were analyzed to elucidate the miniemulsion stabilization and polymerization mechanisms. It was found that the free surfactant concentration exceeded the critical micelle concentration when large amounts of surfactant (60 mM sodium lauryl sulfate) were used, resulting in simultaneous micellar and droplet nucleation. Most surfactant was on the surface of the droplets (85%) or particles (95%). The fractional surface coverage was proportional to the surfactant concentration to the 0.55 power. Using a particle diameter equation, the number of particles was calculated to be proportional to the surfactant concentration to the 1.35 power. Through direct particle size measurements, a power of 1.38 was confirmed. The rate of polymerization was determined by reaction calorimetry to be proportional to the number of particles to the 0.59 power, in contrast to classical Smith–Ewart kinetics for conventional emulsions (1.0 power). The average number of radicals per particle was estimated from the rate and number data, and varied with the particle diameter to the 0.97 power. The observed kinetic dependencies were validated through an extension of Smith–Ewart theory. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3987–3993, 2003     

Online monitoring of the evolution of the number of particles in emulsion polymerization by conductivity measurements. I. Model formulation

A conductivity meter is an inexpensive instrument that can easily be installed in polymerization reactors. This instrument can be used to monitor ionic species without time‐consuming calibrations. A probe is inserted into the media, providing in situ measurements of conductivity in real time. For emulsion polymerization reactions, the conductivity meter can respond to changes in the ionic surfactant concentration, allowing the determination of surfactant dynamics in the media. The surfactant concentration can then be related to the changes in the surface area of the polymer particle phase, which can be linked to nucleation or coagulation phenomena. In this study, a conductivity meter was coupled to a calorimetric reactor to provide in situ and online measurements of conductivity during the emulsion polymerization of styrene, with sodium dodecyl sulfate as an anionic surfactant and with potassium persulfate as a free‐radical initiator. A semiempirical model was built to describe the conductivity signal as a function of the latex composition and the reactor temperature. The model was inverted and combined with the available conductivity signal, conversion, and temperature measurements and was able to accurately predict the number of polymer particles in the latex and the surfactant concentrations in the many phases, without online measurements of the particle size. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1213–1226, 2003     

The inverse emulsion polymerization of acrylamide with pentaerythritolmyristate as emulsifier. 2. Mathematical modelling

A mathematical model of the inverse emulsion polymerization of aqueous acrylamide solutions in isooctane as dispersing media with the chemically pure emulsifier pentaerythritolmonomyristate and an oil-soluble azo initiator has been developed. A Monte Carlo method was used successfully to calculate the kinetics, molar mass averages and average particle sizes. The computation time of the method was reduced by calculating the chain length of the polymer molecules via the life-time of the radicals. It is shown that a few assumptions based on the mirror image of an ideal conventional emulsion polymerization with Smith–Ewart case 2 kinetics are sufficient to comprehensively describe the experimental findings. © 1998 SCI.     

The SCOPE dynamic model for emulsion polymerization I. Theory

The SCOPE dynamic process model has been developed to treat batch and semibatch emulsion copolymerizations. This computer-based model treats jacketed reactors of arbitrary size. It consists of a coupled set of ordinary differential and algebraic equations that describe material balances for the reacting species and energy balances for both the reactor and the cooling water jacket. The model also includes a feature that allows for proportional integral derivative (PID) control of the monomer emulsion and cooling water feed rates to a reactor temperature set point. The model is based largely upon the kinetic theories developed by Smith, Ewart, and Harkins to treat emulsion homopolymerizations. The SCOPE model improves upon and expands the classic theories by taking advantage of recent theoretical developments in emulsion polymerization. Such phenomena as diffusion-controlled termination and radical desorption—important for predicting accurate polymerization rates—are included in the model. More modern theories of particle nucleation, including both homogeneous and micellar mechanisms, have been incorporated into the model to predict accurate particle size distributions. SCOPE also extends the classic theories to treat the emulsion copolymerization of an arbitrary number of monomers. Output from the model includes species concentrations, residual monomer levels, particle size distributions, molecular weight distributions, instantaneous and cumulative copolymer compositions, and reactor temperatures as a function of time. The SCOPE model can be used to evaluate various process control strategies and to study the effects of process dynamics on polymer properties. In Part II, SCOPE model predictions are compared with experimental data for styrene-methyl methacrylate copolymerizations.     

Kinetics of multimonomer emulsion polymerization. The pseudo-homopolymerization approach

By generalizing the Smith–Ewart theory, a system of polymer particle population balances is developed for describing the kinetics of emulsion polymerization processes involving any number of monomer species. Each population is characterized by the number of active radicals of each type present inside each particle, and described through a size distribution function. An approximation procedure is proposed for reducing the original system to that typical of homopolymerization processes, thus characterizing each population-only through the overall number of radicals, without any significant loss of accuracy. The reliability of such “pseudo-homopolymerization approach” is tested by comparison with polymer composition vs. monomer conversion experimental data for the ternary system acrylonitrile–styrene–methyl methacrylate.     

Isothermal emulsion polymerization of n‐butyl methacrylate with KPS and redox initiators: Kinetic study at different surfactant/initiator concentrations and reaction temperature

Thermal initiators, although widely used in emulsion polymerization, are limited to high reaction temperatures due to their high activation energy. Redox initiators have low activation energies indicating that emulsion polymerization could be conducted at lower temperatures to save energy. In the present study, a redox initiator system comprised of hydrogen peroxide (H₂O₂) and ascorbic acid (AA) in conjunction with a Fe²⁺ ion catalyst is compared with a potassium persulfate (KPS) thermal initiator in an emulsion polymerization system consisting of n‐butyl methacrylate (BMA), sodium lauryl sulfate (SLS) and water. The dependence of particle number on surfactant and initiator concentrations shows that redox‐ and KPS‐initiated systems both follow the Smith‐Ewart theory. However, the high radical flux generated from the redox initiator results in the formation of much smaller latex particles and higher reaction rate with lower molecular weights. Latex particle size and molecular weight could also be influenced by reaction temperature. By using redox initiator, small monodisperse particles (diameter < 50 nm) can be achieved without using a large amount of surfactant. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43037.     

Finite volume method as the numerical method for new emulsion polymerization tubular reactor with internal angle baffles

A finite volume method is used to solve a determinist mathematical model and to analyze the performance of an alternative design for an emulsion polymerization reactor with internal angular baffles as static mixer. It is assumed to be a steady‐state, cylindrical one‐dimensional model having a fully developed laminar plug flow. The Smith‐Ewart model is used to estimate the monomer conversion, the kinetics is of Arrhenius type, and laminar finite‐rate model is assumed to compute chemical source terms. The objective of this work is to develop the finite volume method for the new emulsion polymerization tubular reactor with internal angle baffles. The performance of the alternative reactor is compared with continuous tubular reactor with constant reaction temperature. The simulations were validated with experimental results for the isothermal and tubular reactor, with a good concordance. The results with baffles were better than without baffles in relation to desired properties such as particle size and viscosity. The problem is sufficiently well solved by finite volume method. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 6037–6048, 2006     

The preparation of small polystyrene latex particles

The effects of several variables in the preparation of small-sized polystyrene latex particles are described. A semicontinuous preparation using microlatexes obtained by microemulsion polymerization as a seed is compared with a batchwise preparation employing the same ingredients. The particles in the batch products prove to be slightly larger in size but are more narrowly distributed. Furthermore, the effects of both the surfactant type and the ionic strength on the particle size in the batchwise emulision polymerization of styrene are reported. The systems do not obey the linear Smith–Ewart relationship with respect to the micellar surfactant concentration, although in the microemulsion polymerization of styrene the Smith–Ewart relationship is found to be valid with respect to the initiator concentration. Surfactants with a low critical micelle concentration increasingly promote the formation of smaller particle sizes. Salt is found to decrease the particle size when using a strong adsorbing surfactant. However, in the case of a weak adsorbing surfactant, an increase in particle size has been observed above a certain salt concentration.     

Effect of the carboxylic acid monomer type on the emulsifier‐free emulsion copolymerization of styrene and butadiene

Carboxylated styrene–butadiene rubber latexes were prepared through the emulsifier‐free emulsion copolymerization of styrene and butadiene with various carboxylic acid monomers. The effects of various carboxylic acid monomers on the particle formation process were investigated. The type of carboxylic acid monomer strongly affected the particle nucleation. The number of particles and thus the polymerization rate increased with the increasing hydrophobicity of the carboxylic acid monomers. There was a significant difference in the polymerization rate per particle. The results showed that particle nucleation and growth were dependent on the hydrophilic nature of the carboxylic acid monomers. The average particle diameter of the carboxylated styrene–butadiene rubber latexes in the dry state was obtained through some calculations using direct measurements of the average particle diameter in the monomer‐swollen state by a dynamic light scattering technique. Several parameters, such as the polymerization rate, number of latex particles per unit of volume of the aqueous phase, and polymerization rate per particle, were calculated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

A kinetic study of vinyl acetate polymerization in aqueous media in the absence of emulsifier

In the absence of emulsifying agents, vinyl acetate polymerization in aqueous media was carried out at 50°C over a wide range of initial initiator and monomer concentrations to clarify the effect of reaction conditions on the kinetic behavior of the polymerization system. It was shown that the rate of polymerization was proportional to reaction time and initiator concentration and independent of the number of polymer particles present. The rate could also be successfully explained by the Smith and Ewart theory for emulsion polymerization when the dissolved monomer in water and the Trommsdorff effect were taken into consideration. A set of equations which could account for the effect of dissolved monomer in water on the rate of polymerization is proposed.     

高转化率乳聚丁苯橡胶聚合过程中乳液相对分子质量分布与粒径分布考察

采用中石油吉化分公司乳聚丁苯橡胶高转化率大生产配方,考察了实验室聚合反应釜聚合反应单体转化率随反应时间的变化,采用激光粒度分析仪和凝胶渗透色谱仪测定了聚合反应不同单体转化率的胶乳的粒径分布与分子质量分布,结果表明：胶乳粒径呈正态分布,粒径主要集中分布在0.1μm附近,胶乳的平均粒径随反应时间的延长逐渐增大,但是增加的幅度越来越小;聚合反应时间在11 h前（即转化率小于72%）,胶乳的重均分子质量、Z均分子质量一直增大,而数均分子质量变化无明显规律;而分子质量分布宽度指数随反应的进行变小,表明调整的高转化率配方合成的丁苯橡胶可有效改善聚合生成的胶乳粒径分布。     

Acrylic latices stabilized by polymerizable non-ionic surfactant

The final latex particle size is controlled by the concentration of polymerizable non-ionic surfactant NE-40 in the emulsion copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA). The particle size decreases with increasing NE-40 concentration and increases with increasing persulphate initiator concentration. The dependence of particle size on the initiator concentration does not follow conventional Smith–Ewart theory, which is attributed to the bridging flocculation process during the particle nucleation period. The differences in the particle nucleation and growth stages and colloidal stability observed in the NE-40 and nonyl phenol-40 mol ethylene oxide adduct (NP-40) stabilized systems can be attributed to the different distribution patterns of surfactant molecules in the particles. Experimental data also indicate that the particle size decreases with increasing electrolyte concentration, or agitation speed. The total scrap, presumably caused by the bridging flocculation process, increases rapidly with increase in the NaCl concentration The amount of large flocs formed during polymerization is generally greater for the run operated at higher agitation speed. As expected, the latex products stabilized by non-ionic surfactants show excellent stability toward added sodium salt.     

Influence of disproportionated rosin acid soap on the emulsion polymerization kinetics of styrene

The effect of disproportionated rosin acid soap (DRAS) on the emulsion polymerization kinetics of styrene has been studied. Batch experiments reveal a significant influence of chain transfer and limited particle coagulation on the polymerization process. For the recipes studied, the number of growing chains in the emulsion and consequently the polymerization rate were found to be independent of the particle number during the interval of coagulation. However, for relatively large particles (d_p ≈ 100 nm), the polymerization rate was proportional to the particle number, indicating Smith–Ewart case II kinetics. These effects have been shown to be well predicted by model calculations using a radical population balance over the particles. Since DRAS is derived from naturally occurring constituents found in pine trees, its performance, and with that the properties of the product latex, may vary significantly. However, if the performance of DRAS is known, the recipe and process conditions can be optimized. For this reason a procedure has been developed to quantify the performance of DRAS from the simple batch experiments discussed in this paper, the polymerization kinetics, and the information obtained about the coagulation process. © 1995 John Wiley & Sons, Inc.     

Emulsion copolymerization of alpha-methylstyrene and styrene

Fast copolymerizations of styrene and alpha-methylstyrene can be achieved in emulsion systems where free-radical reactions in the bulk or solution are inefficient. The Smith–Ewart–Gardon theory of emulsion polymerization was developed for homopolymerizations but should extend to this copolymerization since the particular comonomers meet the basic assumptions of this model. Sodium lauryl sulfate surfactant provided faster initial polymerization rates, but steady-state conversions were faster with potassium laurate, especially at higher alpha-methylstyrene contents. This is ascribed to acceleration of potassium persulfate decomposition by the former soap. Monomer concentration in the polymerizing particles was constant during steady reaction rates. The rate of volume growth of particles during this interval was generally as predicted by theory. The number of particles and particle sizes could be predicted well if allowance was made for initiator wastage reactions. The observed average number of radicals per particle appeared to be 0.5. Analysis of the composition of monomer droplets and proton NMR analyses of copolymer compositions provided independent confirmations that the present emulsion copolymerization was consistent with the terminal copolymerization model.     

Study on microemulsion polymerization of N‐butyl maleimide

By using sodium dodecyl sulfate (SDS) as an emulsifier, polymerization of N‐butyl maleimide (NBMI) was carried out in ternary oil‐in‐water microemulsion, initiated with potassium persulfate (KPS). The kinetics of microemulsion polymerization were measured by dilatometry. The effects of initiator concentration, polymerization temperature, monomer concentration, and emulsifier concentration on polymerization kinetics were investigated. On this basis, the polymerization kinetics were discussed. The experiment result showed that the microemulsion polymerization kinetics of N‐butyl maleimide were almost consistent with the prediction of the Smith‐Ewart theory in conventional emulsion polymerization, except that the emulsifier showed a special effect on polymerization. At the same time, the polymer was characterized by IR, ¹H‐NMR, DSC, and TGA. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 805–809, 2000     

Effect of carboxylic acid monomer and butadiene on particle growth in the emulsifier-free emulsion copolymerization of styrene-butadiene-carboxylic acid monomer

Carboxylated styrene-butadiene rubber (XSBR) latexes were prepared by emulsifier-free batch emulsion copolymerization of styrene and butadiene with different types of carboxylic acid monomers (AA, MAA, IA). It was found that the particle growth is dependent on the hydrophilic nature of carboxylic acid monomers. SEM studies showed that N_p is almost constant in the particle growth stage (conversion above 10%). Through some calculations by data obtained from DLS technique, average diameter of monomer swollen polymer particles of all the XSBR latexes at the same conversion of 0.4 was obtained to be 368.91, 174.17 and 437.15 nm for AA, MAA and IA, respectively. Several kinetic parameters related to the particle growth stage such as the average number of growing chain per particle were calculated to be 0.474, 0.370 and 1.685 for AA, MAA and IA, respectively. It was observed that these kinetic parameters increase with increasing average diameter of monomer swollen polymer particles, which is consistent with the emulsion polymerization kinetics. Moreover, results indicated that the polymerization rate per particle or equivalently the average number of the growing chain per particle (particle growth stage) decreases by replacing a part of styrene with butadiene in the emulsion copolymerization recipe of styrene-carboxylic acid monomer.