Population Balance Model for Emulsion Polymerisation Under Pseudo-Bulk Conditions: Combined Particle Size Distribution and Molecular Weight Distribution

A comprehensive model for emulsion polymerisation is presented, accounting for particle size distribution (PSD) and molecular weight distribution (MWD). The PSD information is incorporated through a population balance framework. A mechanistic formulation is adopted in modelling the average number of radicals/particle under pseudo-bulk compartmentalisation conditions. The method of moments is adopted to simplify the MWD equations over each discrete size class. The impact of the pseudo-bulk assumption on the PSD and MWD results is assessed. An identification of potential manipulated variables for control of PSD and MWD is done through sensitivity analysis.     

Model Discrimination of Radical Desorption Kinetics in Emulsion Polymerisation

Analysis of published experimental data on monomeric radical diffusion in the emulsion polymerisation of styrene shows that it can be quantitatively described equally well by non‐equilibrium diffusion from particles, where all parameters are derived from properties of the discrete phase, or by steady‐state diffusion where all parameters are derived from properties of the continuous phase. The non‐equilibrium model better describes an observed experimental trend to a reduced desorption rate coefficient at higher weight fraction of polymer in the particles. The theoretical upper bound of the non‐equilibrium model is also higher than the theoretical upper bound of the steady‐state model allowing fits to experimental data which must be discarded as anomalous in the continuous phase model.

     

Diffusion‐Controlled Particle Growth and its Effects on Nucleation in Stirred Emulsion Polymerisation Reactors

Summary: Particle formation and growth in the batch emulsion homo‐polymerisation of styrene and methyl methacrylate monomers under diffusion‐controlled conditions were studied. The polymerisations started with two stratified layers of a monomer and water containing an initiator and a surfactant, with the water layer being gently stirred. Because of limitations in monomer transport, the rate of particle growth was substantially reduced and as a result a large number of polymer particles formed.

Schematic presentation of the highly diffusion‐controlled polymerisation.     

Adaption of the Mechanism of Emulsion Polymerization to New Experimental Results

Summary: New experimental investigations of the 'classical' batch ab-initio emulsion polymerization of styrene reveal the important role of monomer droplets for the whole process. Monomer droplets with a size between a few and some hundreds of nanometers, which are formed by spontaneous emulsification as soon as styrene and water are brought into contact, have a strong influence on the particle nucleation, the particle morphology, and the swelling of the particles. Experimental results confirm that micelles of low molecular weight surfactants are not a major locus of particle nucleation. Brownian dynamics simulations show that the capture of matter by the particles (monomer or radicals) strongly depends on the polymer volume fraction and the size of the captured species (primary free radicals, oligomers, single monomer molecules, or clusters).     

Composite Polymer Nanoparticles via Transitional Phase Inversion Emulsification and Polymerisation

Summary: A new route was employed to produce composite polymer nanoparticles. First, a model polymer (a low molecular-weight polyisobutene) was dissolved in a model monomer (styrene) and then the solution was emulsified in water containing a pair of nonionic surfactants via a transitional phase inversion route. After phase inversion, which produced an oil-in-water miniemulsion, polymerisation of the vinyl monomer gave composite polymer particles. Low temperature emulsification was not practical because the inverted oil-in-water emulsions reinverted to water-in-oil emulsions upon raising the temperature to the reaction temperature. Miniemulsions prepared at the reaction temperature with low monomer content in the oil phase showed good stabilty in the course of polymerisation and produced latexes with a particle size similar to the size of drops in the initial miniemulsions.     

In-Situ Monitoring of Emulsion Polymerisations of MMA and Styrene Using Conductimetry and Calorimetry

In the present work, conductimetry is applied for on-line evaluation of anionic surfactant dynamics during emulsion polymerisation of methyl methacrylate and styrene and for on-line estimation of particle size and number. Reactor and jacket temperatures are used to perform energy balance computations on-line and to provide on-line evaluation of monomer conversion. The parameters of a previously proposed model are re-estimated in order to describe the conductivity signal during methyl methacrylate runs. Some important issues regarding the effects of the surfactant micelles over the conductivity signal are addressed. Finally, the model is inverted and combined with conversion and reactor temperature measurements, providing good predictions of the number of polymer particles in the latex, without needing of on-line measurements of particle size.     

Emulsion Polymerization of Styrene and Vinyl Acetate with Cationic Surfactant

Summary: In this study, the emulsion homopolymerization system containing vinyl acetate and styrene, potassium persulfate, and a new cationic surfactant was studied in the classical glass emulsion polymerization reactor. The effects of new polymeric emulsifier on the physicochemical properties of obtained vinyl acetate and styrene latex properties were investigated depending on surfactant percentage in homopolymerizations.     

有机硅复合乳液聚合的动力学特征和成核机理

研究了聚合方法、搅拌强度、反应温度及原料用量对ＰＨＭＳ／ＢＡ复合乳液聚合反应转化率、反应速率的影响。结果表明：反应前期,一次加料法比半连续滴加法聚合速率快,但反应终了转化率却略低于后者;聚合反应速率随搅拌强度增大略有降低,随反应温度升高而加快,Ｅａ＝１３２．７７ｋＪ／ｍｏｌ;反应的速率和转化率随ＰＨＭＳ用量的增加而降低,随ＮＭＡ用量的增加而升高。乳液粒径随搅拌强度的主粒径追踪结果表明：乳液粒径随搅     

Nucleation in Emulsion Polymerization: Another Step towards Non-Micellar Nucleation Theory

Summary : Comprehensive experimental results of the nucleation stage of styrene emulsion polymerization in the absence as well as in the presence of emulsifier at different concentrations are presented. In addition, the influence of initiator type and presence of seed particles are studied. The nucleation mechanism is verified by means of on-line monitoring of the optical transmission and the conductivity of the aqueous phase. Results prove that micelles do not alter the nucleation mechanism which comprises the initiation of water soluble oligomers in the aqueous phase followed by their aggregation into colloidally stable latex particles. Surfactants assist with nucleation as they lower the activation free energy of particle formation. Contrary, in the presence of seed particles above a critical volume fraction the formation of new particles can be suppressed.     

苯乙烯-甲基丙烯酸羟乙酯无皂乳液聚合过程

苯乙烯-甲基丙烯酸羟乙酯无皂乳液聚合过程;成核机理     

Preparation of a New Polymeric Surfactant for Emulsion Polymerization

The stability of polymeric dispersions is a property of practical importance and hence, the search for an optimized strategy to equip polymer dispersions with sufficient stability is a matter of continuous research during the last years. The kernel is to reach a sufficient stability, as it is required during polymerization, conditioning, or storage and to allow coagulation or coalescence of particles when it is needed, such as during separation of polymer from latex or during film formation. In this study, the emulsion homopolymerization system containing vinyl acetate, potassium persulfate, new polymeric surfactant, NaHCO₃ and water was studied in the classical glass emulsion polymerization reactor. The effects of new polymeric emulsifier on the physicochemical properties of obtained vinyl acetate latex properties were investigated depending on vinyl acetate percentage in homopolymerization.     

Microwave Effects Due to Anionic or Cationic Initiators in Emulsion Polymerization Reactions

Summary: Emulsion polymerization reactions were performed under microwave irradiation and conventional heating using anionic or cationic initiators and surfactants. Microwave irradiation promoted higher reaction rates for both initiators and surfactants, in comparison with the conventional heating. The effect of high power microwave irradiation was studied using a method of cycles of heating and cooling, where rapid polymerization reactions were obtained. In the reactions with anionic initiator and surfactant, a decrease in the particle diameters was observed with microwave heating, and even smaller particles were obtained using high power microwave irradiation. Moreover, the decrease in the particle size was acompanied by an increase in the polymer molecular weight. On the other hand, these effects were not observed for reactions with cationic initiator and surfactant.     

Formation of Nonspherical Particles with Uneven Surface in Emulsion Copolymerization of Styrene and Methacrylic Acid with Nonionic Emulsifier

Summary: Emulsion copolymerization of styrene and methacrylic acid with nonionic emulsifier and potassium persulfate as initiator gave nonspherical copolymer particles having uneven surface. The formation was based on the coagulation of byproduct nano-sized (ca. 35 nm) particles, which were formed throughout the copolymerization until monomer phase disappeared, onto main submicron-sized (234 ∼ 445 nm) particles.     

Emulsion polymerization of divinyl monomers stabilized by sodium dodecyl sulfate and bis(2‐ethylhexyl)sulfosuccinate sodium salt

The emulsion polymerization of divinyl monomers is investigated. Emulsions were obtained in the presence of sodium dodecyl sulfate and bis(2‐ethylhexyl)sulfosuccinate sodium salt as surfactants. The influence of monomer type and kind of surfactant on the particle size distribution is studied. The porous structure of the broken emulsions is also determined. The results indicate that the diameter of nanospheres obtained from two divinyl monomers are significantly larger than those obtained from polystyrene. Aggregation of the particles and the pore‐forming diluent added to the emulsion are responsible for the existence of pores. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3967–3973, 2002     

Simplified Calculation of the Average Number of Radicals Per Particle in Emulsion Polymerization: Effect of Particle Nucleation and Coagulation Rates

The solutions available for the well‐known Smith–Ewart recurrence equation (assuming size monodispersity) for calculating the average number of radicals per particle ( $\overline{n}$) do not consider the contribution of nucleation and coagulation of active particles. Notwithstanding this limitation, they are often used to calculate $\overline{n}$ in simplified mathematical models for commercial simulation software of industrial processes or for process control purposes. In this work, algebraic equations to calculate $\overline{n}$ for 0–1 systems that consider such contributions are developed. It is found that in the nucleation stage under typical conditions of emulsion polymerization, if nucleation and coagulation of particles are not considered in the calculation of $\overline{n}$, it could lead to large errors although its effect still needs to be evaluated in other relevant process parameters as well. However, such significant error could be present for a case of study where secondary nucleation and limited coagulation is experimentally detected.     

Particle Nucleation and Growth in the Emulsion Polymerization of Styrene: Effect of Monomer/Water Ratio and Electrolyte Concentration

This work is an extension of previous research results reported by our team (Colloid and Polymer Science 2013, 291: 2385-2398), where large scale and high solid content latexes of poly(n-butyl acrylate) were obtained with the particle coagulation method induced by the electrolyte. However, how to prepare controlled particle size distribution polymer latex has not been studied. Thus, in this study, the effect of the monomer/water ratios and electrolyte concentrations on particle formation and growth methods were studied by following the tracks of the evolutions of particle size, number and distribution as a function of reaction time or conversion. Experimental results showed that the length of time that particle nucleation occurred increased with increasing monomer charged for the systems without electrolyte. A point worthy of attention here is that homogeneous nucleation may occur at high monomer concentrations (30/70, 40/60). However, electrolyte added could be made the nucleation mechanism shift from micellar/homogeneous nucleation to micelle /coagulation nucleation. As a result, the final particle size distribution can be controlled by adding an appropriate electrolyte to regulate the nucleation mechanism. Spherical and uniformly sized particles could be obtained when electrolyte concentration is between 0.2 wt% and 0.4 wt% for water at the high monomer/water ratio (40/60). The effects of electrolyte concentration on nucleation mechanism mainly were expressed by decreasing the solubility of the monomer and interparticle potential, and then preventing homogeneous nucleation and enhancing particle coagulation.     

Maximum Achievable Particle Size in Emulsion Polymerization: Modeling of Large Particle Sizes

A simplified model for particle formation in emulsion polymerization (comprising aqueous‐phase propagation to degrees of polymerization which may enter a pre‐existing particle and/or form new particles by homogeneous or micellar nucleation, coupled with the aqueous‐phase and intra‐particle kinetics of oligomeric radicals) is formulated to provide a model suitable for the simulation of systems containing large‐sized particles. The model is particularly useful to explore conditions for growth of large particles while avoiding secondary particle formation. Applied to the Interval II emulsion polymerization of styrene with persulfate initiator at 50°C, it is found that there is an effective maximum particle size that can be achieved if the formation of new particles is to be avoided. The parameter space of initiator concentration, particle number concentration and particle radius is mapped to show a “catastrophe” surface at the onset of new nucleation. Advanced visualization techniques are used to interpret the large number of simulations in the series, showing a maximum achievable particle diameter of around 5 μm.     

Emulsion polymerization of styrene using polystyrene‐block‐poly(ethylene oxide) macromonomers as stabilizers

New diblock macromonomers were used as reactive emulsifiers in the emulsion polymerization of styrene. The nature of the reactive group, the molecular weight, the length of the poly(ethylene oxide) (PEO) block, and the molecular structure of the macromonomer were systematically investigated during this process by analyzing the evolution of the conversion and particle diameters. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2819–2827, 2002