Dissertations / Theses on the topic 'Emulsion polymerization'

L’objectif du présent projet est de développer une méthodologie pour la modélisation fondamentale de procédés de polymérisation en émulsion sans tensioactif stabilisés par des particules inorganiques, dénommées "polymérisation en émulsion Pickering". La modélisation des systèmes de polymérisation en émulsion nécessite la modélisation de la distribution de taille des particules (PSD), qui est une propriété importante d'utilisation finale du latex. Cette PSD comprend des sous-modèles dédiés à la nucléation des particules, le transfert de masse entre les différentes phases (monomère, radicaux, stabilisant) et la coagulation des particules. Ces modèles devraient de préférence être validés expérimentalement de manière individuelle. La première partie principale du travail est consacrée à l'étude expérimentale. Cette partie peut être divisée en trois parties. La première partie décrit l'adsorption de particules inorganiques sur le polymère sans réaction. Une adsorption multicouche a été observée et l’isotherme B.E.T. a été capable de décrire cette adsorption. L'adsorption se révèle être plus importante pour une force ionique plus élevée. La dynamique d'adsorption semple être rapide et par conséquent le partage peut être considéré à l'équilibre pendant la polymérisation. La deuxième partie concerne l'étude de différents paramètres de réaction sur le nombre de particules et la vitesse de réaction dans des polymérisations ab initio. L'effet du mélange, de la concentration initiale des monomères et de la concentration de l'initiateur a été étudié. L'optimisation de ces conditions a été utile pour la partie de modélisation. La dernière partie décrit les différences entre plusieurs Laponite® à travers la polymérisation en émulsion ab initio du styrène.La deuxième partie principale du manuscrit a porté sur la modélisation de la polymérisation en émulsion Pickering. Le modèle de bilan de population et le nombre moyen de radicaux par particule ont été calculés en fonction de l'effet des particules organiques. La croissance des particules de polymère a été optimisée en ajustant les modèles d'entrée et de désorption des radicaux décrits dans la littérature aux données expérimentales. Aucune modification n'a été nécessaire, ce qui nous a permis de conclure que l'argile n'avait aucune influence sur l'échange radical. Cependant, la stabilisation joue un rôle important dans la production de particules de polymère. Le modèle de nucléation coagulante a été capable de décrire le taux de nucléation et de prédire le nombre total de particules
The aim of the present project is to develop a methodology for fundamental modeling of surfactant-free emulsion polymerization processes stabilized by inorganic particles, referred to as “Pickering emulsion polymerization”. Modeling emulsion polymerization systems requires modeling the particle size distribution (PSD), which is an important end-use property of the latex. This PSD includes submodels dedicated to particle nucleation, mass transfer between the different phases (monomer, radicals, stabilizer), and particle coagulation. These models should preferably be individually identified and validated experimentally. The first main part of the work is dedicated to the experimental study. This part can be divided in three parts. The first part describes the adsorption of inorganic particles on polymer without reaction. Multilayer adsorption was observed and B.E.T. isotherm was able to describe this adsorption. The adsorption was found to be enhanced at higher ionic strength. The adsorption dynamics were found fast and therefore clay partitioning can be considered at equilibrium during polymerization. The second part concerned the investigation of different reaction parameters on the particles number and reaction rate in ab initio polymerizations. The effect of mixing, initial monomer concentration and initiator concentration were considered. Optimization of these conditions was useful for the modeling part. The last part described the differences between several LaponiteR_ grades through the ab initio emulsion polymerization of styrene. The second main part of the manuscript focused on the modeling of the Pickering emulsion polymerization. The population balance model and average number of radicals balance were adapted regarding the effect of inxi organic particles. The growth of the polymer particles was optimized by fitting the models of radicals’ entry and desorption described available in literature to the experimental data. No modification was needed, which allowed us to conclude that the clay had no influence on radical exchange. However, LaponiteR_ stabilization played an important role in polymer particles production. Coagulative nucleation model was able to describe the nucleation rate and predict the total number of particles

Les travaux présentés dans cette thèse portent sur la polymérisation radicalaire de l'éthylène en émulsion, dans des conditions douces (P < 250 bar et T < 90 °C). Tout d'abord, l'homopolymérisation de l'éthylène a été étudiée. Des latex stables de polyéthylène présentant des taux de solide relativement élevés (30 %) ont été obtenus. Pour cela, deux systèmes différents d'amorçage et de stabilisation (cationique et anionique) ont été employés. Ces latex peuvent trouver des applications comme revêtements hydrophobes (par exemple du papier). L'étude des propriétés thermiques des latex a mis en évidence des phénomènes de cristallisation du polyéthylène à basse température, dû à son confinement dans les nanoparticules. Cela a une forte influence sur les morphologies finales des particules. D'autre part, la copolymérisation radicalaire de l'éthylène en émulsion a été étudiée. Les comonomères utilisés sont le styrène, l'acrylate de butyle, le méthacrylate de méthyle et l'acétate de vinyle qui différent par leur solubilité dans l'eau et leurs rapports de réactivité de copolymérisation avec l'éthylène. La composition des copolymères obtenus influence leurs propriétés thermiques (Tg, Tf). Des latex stables de copolymères de compositions variées ont pu ainsi être synthétisés. Ce travail en homo- et copolymérisation a souligné la complexité des milieux de polymérisation en émulsion impliquant un monomère gazeux supercritique comme l'éthylène
In this work, the free radical emulsion polymerization of ethylene under mild conditions (P < 250 bar and T < 90 °C) was investigated. Ethylene homopolymerization was first studied. Stable polyethylene latexes of significantly high solids content (30 %) were produced. This was achieved by the use of two different initiating and stabilizing systems (cationic and anionic). These latexes could be applied as hydrophobic coatings (e.g. on paper). Investigation of the thermal properties of the latexes evidenced crystallization phenomena at low temperatures, owing to PE confinement in the nanoparticles, which strongly impacted their final morphologies. Free radical emulsion copolymerization of ethylene was then studied. The investigated comonomers were styrene, butyl acrylate, methyl methacrylate and vinyl acetate. They differ in their reactivity ratios to ethylene and their water solubility. The composition of the obtained copolymers had a strong influence on their thermal properties (Tg, Tm). Stable latexes containing copolymers of various compositions were thus synthesized. This work on homo- and copolymerization evidenced the complexity of the polymerization media involving a gaseous supercritical monomer such as ethylene

Abstract This work investigates the kinetics of the emulsion polymerization of vinyl acetate. Several aspects of this system have been clarified, including the induced decomposition of persulfate, retardation by oxygen and entry by, and analysis of, the aqueous phase oligomeric radicals. It has been shown that the retardation period observed in the emulsion polymerization of VAc can be explained by the effect of traces of oxygen (< 10-6 M) on the entry efficiency of the initiator-derived aqueous-phase oligomeric radicals. Comparison of rates of polymerization in V and persulfate -initiated polymerizations together with electrospray mass spectrometry of aqueous phase oligomers, has shown that the mechanism for the induced decomposition of persulfate by vinyl acetate is chain transfer to initiator from aqueous-phase oligomeric radicals. A value has been determined for the rate coefficient for transfer to initiator, by fitting literature data to a model based on this mechanism. The reported independence of the rate of polymerization from the monomer concentration in the emulsion polymerization of vinyl acetate has been investigated. Possible explanations for this behaviour have been proposed and tested in this work, by measuring radical-loss rates directly with y-relaxation techniques. Although the Y relaxations were found to be affected by experimental artefacts, it has been demonstrated that rapid exit is not responsible for the high radical-loss rates in this system. The major artefact identified in the y relaxations was the significant effect of relatively small exotherms on relaxation behaviour, Methodologies were developed for correcting affected data and for avoiding exotherms under certain conditions. Arrhenius parameters were determined for the rate coefficient for chain transfer to monomer using the In^M method, which utilises the whole MWD. This section of the work is incomplete, for reasons detailed in chapter 5. However, as a preliminary indication it was found that the frequency factor was 106.38 M-1 s-1 and the activation energy was 38.8 kJ mol-1.

Abstract This work investigates the kinetics of the emulsion polymerization of vinyl acetate. Several aspects of this system have been clarified, including the induced decomposition of persulfate, retardation by oxygen and entry by, and analysis of, the aqueous phase oligomeric radicals. It has been shown that the retardation period observed in the emulsion polymerization of VAc can be explained by the effect of traces of oxygen (< 10-6 M) on the entry efficiency of the initiator-derived aqueous-phase oligomeric radicals. Comparison of rates of polymerization in V and persulfate -initiated polymerizations together with electrospray mass spectrometry of aqueous phase oligomers, has shown that the mechanism for the induced decomposition of persulfate by vinyl acetate is chain transfer to initiator from aqueous-phase oligomeric radicals. A value has been determined for the rate coefficient for transfer to initiator, by fitting literature data to a model based on this mechanism. The reported independence of the rate of polymerization from the monomer concentration in the emulsion polymerization of vinyl acetate has been investigated. Possible explanations for this behaviour have been proposed and tested in this work, by measuring radical-loss rates directly with y-relaxation techniques. Although the Y relaxations were found to be affected by experimental artefacts, it has been demonstrated that rapid exit is not responsible for the high radical-loss rates in this system. The major artefact identified in the y relaxations was the significant effect of relatively small exotherms on relaxation behaviour, Methodologies were developed for correcting affected data and for avoiding exotherms under certain conditions. Arrhenius parameters were determined for the rate coefficient for chain transfer to monomer using the In^M method, which utilises the whole MWD. This section of the work is incomplete, for reasons detailed in chapter 5. However, as a preliminary indication it was found that the frequency factor was 106.38 M-1 s-1 and the activation energy was 38.8 kJ mol-1.

Particle formation in RAFT-mediated emulsion polymerization has been studied using reaction calorimetry. By measuring the heat flow during controlled feed ab-initio emulsion polymerization in the presence of amphipathic RAFT agents, particle formation by self-assembly of these species could be observed. Two different monomer systems, i.e. styrene and n-butyl acrylate, and various degrees of hydrophobicity of the initial macro-RAFT agents have been studied and compared. The different macro-RAFT agents were synthesized by first forming a hydrophilic block of poly(acrylic acid) that would later on act as the electrosteric stabilizing group for the particles. Subsequently, different lengths of hydrophobic blocks were grown at the reactive end of the poly(acrylic acid) hydrophilic block via the RAFT-mediated controlled radical polymerization, either comprised of n-butyl acrylate or styrene. Two processes govern particle formation: adsorption of macro-RAFT agents onto growing particles and formation of new particles by initiation of micellar aggregates or by homogeneous nucleation. Competition between these processes could be observed when monomers with a relatively high (n-butyl acrylate) or low (styrene) propagation rate coefficient were used. A model describing particle formation has been developed and the results of model calculations are compared with experimental observations. Preliminary modeling results based on a set of reasonable physico-chemical parameters already showed good agreement with the experimental results. Most parameters used have been verified experimentally. The development of the molecular weight distribution of the macro-RAFT agents has been analyzed by different techniques. Quantification of the particle formation process by analytical techniques was difficult, but qualitative insights into the fundamental steps governing the nucleation process have been obtained. The amount of macro-RAFT agents initially involved in particle formation could be determined from the increase of molecular weight. The particle size distribution has been measured by capillary hydrodynamic fractionation, transmission electron microscopy and dynamic light scattering. From the data obtained from these particle-sizing techniques, the number of particles during the reaction could be monitored, leading to an accurate estimate for the particle formation time. Upon implementation of the experimental data obtained for the surface active macro-RAFT systems, the model demonstrated to be very sensitive towards the “headgroup” area of the macro-RAFT species. Three nucleation cases based on the initial surface activity of the macro-RAFT species in the aqueous phase are proposed to explain the deviations from the assumptions of the nucleation model. Even though the macro-RAFT species have a narrow molecular weight distribution, they are nevertheless made up of a distribution of block lengths of polystyrene upon a distribution of block lengths of poly(acrylic acid). The resulting differences in initial surface activity are the most probable reason for the observed differences between model calculations and experimental results for the nucleation time and particle size distribution of the final latex product. With the procedure described above, latexes have been synthesized without using conventional surfactants and the mechanisms involved in the particle formation for these systems have been elucidated. The results of this work enable production of latex systems with well defined molecular mass distributions and narrow particle size distributions. Furthermore, the technique based on the application of amphipathic RAFT agents is promising for the production of complex polymeric materials in emulsion polymerization on a technical scale.

Doctor of Philosophy(PhD)
Particle formation in RAFT-mediated emulsion polymerization has been studied using reaction calorimetry. By measuring the heat flow during controlled feed ab-initio emulsion polymerization in the presence of amphipathic RAFT agents, particle formation by self-assembly of these species could be observed. Two different monomer systems, i.e. styrene and n-butyl acrylate, and various degrees of hydrophobicity of the initial macro-RAFT agents have been studied and compared. The different macro-RAFT agents were synthesized by first forming a hydrophilic block of poly(acrylic acid) that would later on act as the electrosteric stabilizing group for the particles. Subsequently, different lengths of hydrophobic blocks were grown at the reactive end of the poly(acrylic acid) hydrophilic block via the RAFT-mediated controlled radical polymerization, either comprised of n-butyl acrylate or styrene. Two processes govern particle formation: adsorption of macro-RAFT agents onto growing particles and formation of new particles by initiation of micellar aggregates or by homogeneous nucleation. Competition between these processes could be observed when monomers with a relatively high (n-butyl acrylate) or low (styrene) propagation rate coefficient were used. A model describing particle formation has been developed and the results of model calculations are compared with experimental observations. Preliminary modeling results based on a set of reasonable physico-chemical parameters already showed good agreement with the experimental results. Most parameters used have been verified experimentally. The development of the molecular weight distribution of the macro-RAFT agents has been analyzed by different techniques. Quantification of the particle formation process by analytical techniques was difficult, but qualitative insights into the fundamental steps governing the nucleation process have been obtained. The amount of macro-RAFT agents initially involved in particle formation could be determined from the increase of molecular weight. The particle size distribution has been measured by capillary hydrodynamic fractionation, transmission electron microscopy and dynamic light scattering. From the data obtained from these particle-sizing techniques, the number of particles during the reaction could be monitored, leading to an accurate estimate for the particle formation time. Upon implementation of the experimental data obtained for the surface active macro-RAFT systems, the model demonstrated to be very sensitive towards the “headgroup” area of the macro-RAFT species. Three nucleation cases based on the initial surface activity of the macro-RAFT species in the aqueous phase are proposed to explain the deviations from the assumptions of the nucleation model. Even though the macro-RAFT species have a narrow molecular weight distribution, they are nevertheless made up of a distribution of block lengths of polystyrene upon a distribution of block lengths of poly(acrylic acid). The resulting differences in initial surface activity are the most probable reason for the observed differences between model calculations and experimental results for the nucleation time and particle size distribution of the final latex product. With the procedure described above, latexes have been synthesized without using conventional surfactants and the mechanisms involved in the particle formation for these systems have been elucidated. The results of this work enable production of latex systems with well defined molecular mass distributions and narrow particle size distributions. Furthermore, the technique based on the application of amphipathic RAFT agents is promising for the production of complex polymeric materials in emulsion polymerization on a technical scale.

Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Jones, Christopher W.; Committee Chair: Schork, F. Joseph; Committee Member: Koros, William J.; Committee Member: Lyon, Andrew; Committee Member: Nenes, Athanasios. Part of the SMARTech Electronic Thesis and Dissertation Collection.

This thesis is a contribution to the development of population balance models of emulsion polymerization and, more particularly, to the modeling of particle formation and particle size distribution (PSD) in vinyl chloride emulsion polymerization. The rst part of the work is dedicated to the acquisition of experimental data. Ab initio polymerizations were done to obtain reliable data regarding the dependence of the particle number on the concentration of surfactant, as well as to analyze the effect of the initiator concentration, stirring rate, and monomer-to-water ratio upon the particle number and the polymerization kinetics. In addition, seeded polymerizations were carried out at different concentrations of seed latex and emulsifier in order to quantify the influence of these factors on the onset and extent of secondary particle formation. Moreover, the adsorption isotherms of SDS and SDBS on poly (vinyl chloride) latex particles were determined. The second part of the manuscript focuses on the development of the population balance model. A special feature of the model proposed in this work is the computation of the coupled radical number and particle size distributions by the zero-one-two population balance equations. Overall, the examples presented show that the model can capture the tendencies observed in the polymerizations with physically reasonable values of the unknown/ adjustable parameters. With respect to particle formation, it was seen that including the possibility of particle nucleation (homogeneous and micellar) by exited radicals helps to explain the high particle numbers observed and the fact that the initiator concentration has a negligible effect on the particle number. Moreover, it was demonstrated that particle coagulation must be taken into account in order to obtain plausible PSDs and to avoid the use of abnormally low values of the efficiency of radical entry into micelles. In the third and last part, two novel numerical methods for the solution of population balances of interest to emulsion polymerization systems are presented and discussed
Cette thèse est une contribution au développement de modèles mécanistiques de la polymérisation en émulsion et, plus particulièrement, une contribution à la modélisation de la formation des particules et de leur distribution de taille (DTP) lors de la polymérisation en émulsion du chlorure de vinyle. La première partie de l'étude est consacrée à l'obtention de données expérimentales. Des polymérisations ab initio ont été réalisées afin d'obtenir des données fiables sur l'effet de la concentration de tensioactif, concentration d'initiateur, vitesse d'agitation et rapport monomère/eau sur le nombre de particules formées et sur la cinétique de polymérisation. Des polymérisations ensemencées ont également été réalisées afin de déterminer l'influence de la quantité de semence et de la concentration de tensioactif sur la formation de particules par nucléation secondaire. Enfin, les isothermes d'adsorption du SDS et du SDBS sur des particules de latex de poly (chlorure de vinyle) ont été déterminées. La deuxième partie de l'étude concerne le développement et la validation du modèle de polymérisation. Celui-ci à la particularité d'utiliser les bilans de population propres aux systèmes ‘zéro-un-deux' pour déterminer la distribution jointe du nombre de radicaux et de la taille des particules. Dans l'ensemble, les résultats obtenus montrent que le modèle proposé est capable de décrire les principaux comportements retrouvés lors des polymérisations avec des valeurs physiquement plausibles des paramètres inconnus ou ajustables. Pour ce qui concerne la formation des particules, il s'avère que la prise en compte de la possibilité de nucléation (homogène ou micellaire) par les radicaux désorbés aide à expliquer les valeurs élevées du nombre de particules ainsi que l'effet négligeable de la concentration d'initiateur sur le nombre de particules. En autre, il est démontré que le phénomène d'agrégation des particules doit être pris en considération afin d'obtenir des DTPs cohérentes. Dans la troisième et dernière partie, deux nouvelles méthodes numériques pour la résolution de bilans de population d'intérêt pour la modélisation des systèmes de polymérisation en émulsion sont proposées et analysées

Le développement d’un procédé de polymérisation en émulsion est complexe de par la nature hétérogène de ce type de réaction. En outre, dans le cas de la polymérisation en émulsion du fluorure de vinylidène, la difficulté est d’autant plus accrue que le monomère est habituellement en phase gazeuse ou supercritique dans les conditions d’intérêt. Or la littérature manque d’informations concernant ce type de procédé de synthèse du PVDF sous une pression comprise entre 30 bar et 90 bar.Ainsi cette thèse a pour objectif de contribuer à une meilleure compréhension des mécanismes cinétiques et de stabilisation intervenants dans la polymérisation radicalaire en émulsion du VDF dans des conditions supercritiques et, plus particulièrement, de fournir des données expérimentales nécessaires à l’élaboration de futurs modèles.Avant même d’entreprendre les études expérimentales, cette thèse s’intéresse d’abord aux aspects d’installation et d’automatisation de l’unité de polymérisation ainsi qu’au démarrage et à l’optimisation du réacteur. Ensuite, plusieurs tests sont réalisés afin de comprendre certaines caractéristiques du latex produit ainsi que certaines propriétés du tensioactif fluoré. Une nouvelle méthode a spécialement été développée afin de suivre le phénomène de coagulation des particules de polymère.Finalement des réactions sont réalisées par lot et en semi-continu et une étude paramétrique des conditions opératoires et de la composition des réactifs est effectuée afin d’évaluer leur impact sur l’évolution de la polymérisation en émulsion. Notamment, le profil de vitesse de polymérisation est obtenu par calorimétrie, à partir d’une approche pratique fondée sur un estimateur d’état en cascade, ainsi que sur la mesure de la consommation de monomère, et sur l’analyse gravimétrique réalisée par prélèvement
The heterogeneous nature of the conventional emulsion polymerization can render the process quite complex. In the case of the emulsion polymerisation of vinylidene fluoride (VDF), the situation is more complicated than for the majority of industrial processes because the monomer is typically either a gas or a supercritical fluid under the polymerization conditions of interest. Given the relatively high pressure required for this process (30bar

The kinetics of electrosterically stabilized emulsion systems was studied. The aim of this was to understand the impact that steric and electrosteric stabilizers have on the kinetics of particle growth and particle formation in the area of emulsion polymerization. The well-established mechanisms that govern these processes for emulsions stabilized by conventional low molecular weight surfactants were used as a reference point for comparative purposes. Model latexes were synthesized that comprised of a poly(styrene) core stabilized by a corona of poly(acrylic acid). The advent of successful controlled radical polymerization techniques in heterogeneous media (via RAFT polymerization) allowed for latexes to be synthesized under molecular weight control. For the first time, the degree of polymerization of the stabilizing block on the particle surface was able to be controlled and verified experimentally using mass spectrometry techniques. Three latexes were made with different average degrees of polymerization of the stabilizing block; five, ten and twenty monomer units respectively. A methodology was developed to remove the RAFT functionality from the polymer chains present in the emulsion while retaining the desired particle morphology. Oxidation with tertbutylhydroperoxide (TBHP) was proven to be successful at eliminating the living character provided by the thiocarbonyl end-group. Extensive dialysis and cleaning of the latex was performed to ensure no residual TBHP or reaction by-products remained. Latexes with poly(styrene) cores were chosen for this work as poly(n-butyl acrylate) latexes were shown to be influenced by chain transfer to polymer, providing an additional kinetic complication. The three electrosterically stabilized emulsions were used as seed latexes in carefully designed kinetic experiments to measure the rate of polymerization as a function of time. Two independent techniques (chemically initiated dilatometry and γ-relaxation dilatometry) were used to measure the rate coefficients of radical entry (ρ) and exit (k) in these systems – the two parameters that essentially govern the rate of particle growth. The latexes were chosen such that they satisfied ‘zero-one’ conditions (i.e. that any given latex particle contains at most one growing radical at any given time) in order to simplify data analysis. Three different chemical initiators were used, each yielding a radical with a different electric charge. Results from γ-relaxation experiments demonstrated that the three electrosterically stabilized latexes gave very long relaxation times when removed from the radiation source, ultimately yielding very small k values. These values were up to a factor of 10 smaller than that predicted by the ‘transfer-diffusion’ model for exit for particles of that size. This reduction was attributed to a ‘restricted diffusion’ effect, where the exiting monomeric radical has to diffuse through a dense layer of polymer on the particle surface, where its mobility will be restricted. Modification of the Smoluchowski equation for diffusion-controlled adsorption/desorption to account for this postulate led to the development of a model that gave excellent semi-quantitative agreement with experiment. Chemically initiated dilatometric experiments (using three different types of initiator) gave the unusual result of very low reaction rates and low steady-state values of 'nbar', the average number of radicals per particle. Using the standard kinetic equations for styrene-based systems (where it is assumed that an exited monomeric radical undergoes re-entry), this led to the calculation of impossibly small values of the entry rate coefficient ρ (far below any background or ‘thermal’polymerization rate). However upon removing the assumption of re-entry and assuming that exited radicals undergo termination, the obtained values of ρ were in almost perfect agreement with the values predicted from the ‘control by aqueous phase growth’ entry mechanism. This unexpected result was attributed to chemical reaction with the poly(acrylic acid) stabilizers through chain transfer to polymer (via hydrogen-atom abstraction). This postulate was verified by separate experiments that demonstrated that poly(acrylic acid) could act as a reasonably efficient chain transfer agent for styrene polymerization. The addition of poly(acrylic acid) to the aqueous phase of a conventionally stabilized emulsion also led to the rate reduction seen previously. NMR experiments demonstrated the existence of poly(acrylic acid-graft-styrene), which could only be formed through termination of a poly(styrene) chain with a poly(acrylic acid) chain bearing a mid-chain radical (as the product of a chain transfer reaction). These additional terms of transfer and termination were included in the governing kinetic equations of emulsion systems (the Smith-Ewart equations) to develop a model to account for the behaviour of electrosterically stabilized latexes. The ultimate fate of an exiting radical was now shown to be a competition between fates; successful desorption into the aqueous phase, or chemical reaction (through transfer or termination) within the hairy layer. These additional terms were shown to significantly reduce the theoretical value of nbar, and were in excellent agreement with experiment. For small electrosterically stabilized particles with a densely packed ‘hairy layer,’ it was seen that transfer/termination is the dominant loss mechanism as opposed to desorption. The developed model showed that as the particle size was increased, the dominant loss mechanism once again became successful desorption into the aqueous phase. The model was shown to give excellent agreement with experimental data from ‘uncontrolled’ emulsion systems. To explain the highly unusual secondary nucleation behaviour seen in systems such as these, it was postulated that beta-scission of a poly(acrylic acid) chain bearing a mid-chain radical is an important mechanistic step in the nucleation mechanisms of these systems. Modelling (both steady-state and time-dependent) gave good agreement with experiment with a minimal number of adjustable parameters. Theory (and supporting experimental evidence) demonstrated that this nucleation mechanism is only significant at high particle numbers; under other conditions the well-known ‘homogeneous nucleation’ mechanism is once again dominant.

A direct emulsion process was performed for the synthesis of an emeraldine salt of polyaniline (PANI) us-ing a novel surfactant, namely cetyl dimethyl ammonium phenyl chloride (CDAPhCl). HCl was used as do-pant and potassium persulfate (KPS)was used as an oxidizing agent. Variation of polymer yield was recorded using conventional gravimetric method and resulting polymer salt was analyzed by FTIR. Average particle size and latex morphology was studied using dynamic light scattering (DLS) and scanning electron microsco-py (SEM).Furthermore, the influence of the reaction time followed by polymer yield on the conductivity of re-sulted PANI salt was investigated. SEM images showed a nanostructured polyaniline and conductivity of the polyaninle film found to be 1.65 S cm-1. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35633

Polyacrylamides (PAAMs) including both homo- and copolymers of acrylamide constitute the largest group of water soluble polymers which are used in various industrial applications. The common industrial method for the synthesis of high molecular weight PAAMs is inverse emulsion polymerization (IEP); however, considerable disagreement exists regarding the mechanism of IEP. Besides, the high polymerization rate of acrylamide has made the controllability of this system challenging for the industry. A new IEP recipe for synthesis of polyacrylamide using an industrial solvent (D80) and oil soluble initiator azobisiosbutyronitrile (AIBN) was developed in this study. The samples from the IEP reactor were monitored using TEM and optical microscopy for particle size and structure of latex while gravimetric method was applied for monitoring monomer conversion. The results indicated that the locus of reaction is micelles; however, with an increase in initiator concentration or a decrease in emulsifier concentration, the droplets also serve as loci of polymerization. As the alteration of electrical properties with any reaction is rapid, the novel idea of following IEP reactor using electrical impedance spectroscopy (EIS) was examined. Firstly, EIS successfully could detect critical micelle concentration of the emulsifier in the oils. We found that at the CMC a transition in conductance-concentration graph of the emulsifier/oils mixture at 1Hz occurs. From the slope of the graph after CMC, characteristics of the micelles were deduced. More importantly, we found that by using EIS it is feasible to monitor the key parameters of polymerization, such as monomer conversion and particles size and their number. The comparison of electrical responses of IEP using the oil soluble initiator with the redox initiator with definite droplet nucleation confirmed that droplet or micellar nucleation can be distinguished from electrical response of the reaction

Methods to prepare anisotropic or Janus particles are well documented. However, the preparation methods available to prepare polymeric Janus nanoparticles still suffer from significant challenges. In this Thesis, three methods are explored to synthesize polymeric Janus nanoparticles with amphiphilic properties. In the Janus nanoparticles prepared, one side is hydrophilic, being coated by a “hairy” layer of poly(acrylic acid) (AA) and one side is hydrophobic, being made of styrene (Sty) or 2,2,2-triflioroethyl methacrylate (TFEMA). The first method described the synthesis of anisotropic or Janus nanoparticles from seed particles prepared through the self-assembly of amphiphilic diblock copolymers using solvent exchange method. The ability of the amphiphilic diblock copolymers to self-assemble into seed particles depended on the ratio between the hydrophobic and hydrophilic blocks. Using a fixed ratio between the hydrophobic and hydrophilic block of 4.9 and 4.8 respectively, the amphiphilic diblock copolymers, PABTC-(Sty)49-b-(AA)10 and PABTC-(Sty)87-b-(AA)18 self-assembled, forming seed particles with a diameter of 14 and 19 nm respectively. These particles were then swollen with different amounts of cross-linker, divinylbenzene (DVB), producing cross-linked seed particles. The cross-linked seed particles were then swollen with DVB/styrene or tetraethylene glycol diacrylate (TEGDA)/TFEMA mixtures, which were added by batch addition at room temperature before polymerizing at high temperature. For the smallest seed particles of 14 nm, higher amounts of cross-linker imparted lower surface active property on the anisotropic particles once swollen and polymerized with TEGDA/TFEMA. The contrary was true for larger seed particles of 19 nm. The anisotropic particles with a TEGDA/TFEMA bulge were very surface active, therefore markedly amphiphilic. Anisotropic particles made from the 19 nm seed particles were more surface active than those made from 14 nm seed particles, due to their ability to form bigger hydrophobic bulge. Through the method described here, amphiphilic Janus nanoparticles as small as 17 nm measured through the longest dimension were synthesized. The second method studied produced seed particles by the continuous addition of styrene into a micelles solution of PABTC-(nBA)5-b-(AA)5 under basic conditions. Using this approach, the seed particles prepared had an average size of 21 nm. The seed particles were then cross-linked using DVB, before styrene was added continuously to the cross-linked seed latex to yield anisotropic particles. The size of the bulge was conveniently adjusted by the amount of monomer being fed and was not restricted by the size of the cross-linked seed particles. Once the bulge of the anisotropic particles prepared was cross-linked, tri-lobed anisotropic nanoparticles were synthesized. The continuous monomer addition method produced shape anisotropic particles at high solid content and was more convenient and simple than the batch method. The flexibility of the continuous addition method made it attractive for application in industry. The drawback of this method was that large micrometric polymer beads were formed as well during the seed particles synthesis, which needed to be removed by centrifugation. And finally, miniemulsion polymerization was used to synthesize cross-linked seed particles. This approach proved to be advantageous over the continuous addition method, with no micrometric polymer beads observed during the seed latex synthesis. As DVB was added during the homogenization of the monomer and amphiphilic diblock copolymer, the cross-linked seed was conveniently polymerized in a single step. Styrene was then added by batch or in a continuous manner, while TFEMA was added only by batch. The size of the bulge formed increased with the continuous addition of styrene to the cross-linked seed latex. The anisotropic/Janus nanoparticles prepared with a TFEMA bulge imparted the largest reduction on the surface tension of water. The anisotropic or Janus nanoparticles prepared by the continuous addition of styrene were less surface active than those prepared using batch addition of styrene. The decomposition products resulting from the water-soluble initiator used rendered the bulge produced more hydrophilic, resulting in particles with lower surface active properties than expected. Miniemulsion polymerization was a simpler and quicker method to form the cross-linked seed particles compared to the other two methods tested, eliminating the need to purify the seed latex from large micrometric polymer beads as required in the second method. Through the methods described in this Thesis, it was possible to synthesis for the first time small amphiphilic Janus nanoparticles of less than 20 nm measured through the longest dimension. Shape anisotropic particles and amphiphilic Janus particles of more than 40 nm could be directly used in industrial applications thanks to the fast and simple synthesis method and in the case of continuous addition, to the high solid content of particles synthesized.

La nécessité de produire des polymères avec des propriétés spécifiques et reproductibles, de minimiser le temps et les coûts et de contrôler la sécurité de l'expérience nous contraint à utiliser des méthodes avancées de contrôle de procédés de polymérisation.

Les polymères sont aujourd'hui utilisés dans des domaines différents. Une grande partie de ces polymères est produite en émulsion. La formulation de base d'une réaction de polymérisation en émulsion classique, contient de l'eau qui constitue la phase continue, et des monomères qui sont dispersés dans l'eau et stabilisés grâce à un agent émulsifiant. Les particules de polymère ainsi produites sont suspendues dans l'eau, grâce à l'émulsifiant. Le milieu résultant est donc appelé 'latex'.

Les propriétés du latex dépendent de beaucoup de paramètres, tels que la distribution de la masse molaire de polymère, la distribution des tailles de particules, la température de transition vitreuse, la morphologie, et la composition du polymère, si la réaction fait intervenir plusieurs monomères. Ces propriétés sont influencées par plusieurs variables, la nature et la quantité des additifs tels que, l'amorceur, le tensioactif les agents de transfert éventuels, la façon dont ces produits et les monomères sont introduits dans le réacteur, la température de la réaction, l'agitation, et le type de réacteur utilisé. Ces nombreuses variables sont alors nos variables de commande, que nous devons faire varier pour obtenir les propriétés désirées.

En réalité, afin d'obtenir des propriétés spécifiques, tout en assurant la sécurité du procédé, plusieurs paramètres sont fixés a priori, tels que la quantité initiale de réactifs et la température de la réaction. Ceci dit, plusieurs paramètres restent à faire varier en ligne, pendant la réaction, comme la température de la double enveloppe, pour maintenir la réaction à la température prévue, et le débit d'ajout des monomères, qui nous permettront de contrôler les propriétés du latex (la taille des particules et la composition du polymère). Ce genre d'intervention en ligne pour améliorer la qualité et la sécurité du procédé, le contrôle en ligne du procédé de polymérisation en émulsion, sont l'objet but principal de ce travail.

Du point de vue du contrôle, le procédé est un système dynamique (représenté par des équations différentielles) possédant des entrées, des états (les variables décrivant l'évolution du procédé), et finalement des sorties (qui sont les variables mesurées en ligne, et sont en général, une combinaison des états du système).

Pour contrôler un procédé, un modèle représentatif de ce procédé est nécessaire. Faute de trouver un modèle parfait du procédé, des informations en ligne provenant des sorties du système, s'avèrent nécessaires pour accomplir la stratégie de contrôle. En réalité, les raisons pour lesquelles, les méthodes de contrôle avancées n'ont pas été utilisées lors des procédés de polymérisation en émulsion sont le manque de capteurs en ligne capables de donner des mesures pour la plupart des propriétés des polymères, la rapidité de la réaction, la sensibilité de la réaction à la présence de petites quantités d'additifs, la nonlinéarité du modèle du procédé et le grand nombre de paramètres inconnus dans le modèle et l'interaction entre ces paramètres.

Une des propriétés intéressantes à contrôler lors des procédés de polymérisation en émulsion, est la composition du polymère, pour les procédés faisant intervenir plusieurs monomères à une composition non azéotropique. La composition du polymère intervient au niveau de la détermination de la température de transition vitreuse, des propriétés mécaniques, ainsi que de la morphologie du polymère. Il a été trouvé dans la littérature que l'ajout du monomère le plus réactif à des débits variables est la méthode la plus efficace pour contrôler la composition tout en assurant une vitesse de réaction relativement élevée. En utilisant une méthode avancée de contrôle, nous pouvons alors maintenir la composition à une valeur désirée. Ceci nécessite une connaissance approfondie du procédé ainsi que la mesure en ligne de la composition de polymère.

Les capteurs en ligne utilisés pour suivre les procédés de polymérisation en émulsion peuvent être divisés en deux catégories: des capteurs nécessitant une boucle de circulation externe, ou un système de prise d'échantillons afin d'effectuer l'analyse (Chromatographie en phase gazeuse, densimétrie); et des capteurs in situ qui effectuent les analyses dans le réacteur (Spectroscopie Infrarouge, sondes ultrasons). La chromatographie en phase gazeuse peut être utilisée pour mesurer, en ligne, la composition du mélange de monomère résiduel, si le réacteur est équipé d'un système automatique de prise d'échantillons, de dilution, dans certains cas, et d'injection dans le chromatogramme. La densimétrie a été également utilisée pour la mesure en ligne de la composition du polymère. Une boucle de circulation du latex dans l'appareil est donc indispensable pour effectuer l'analyse. Cependant ces deux méthodes présentent quelques difficultés expérimentales, telles que la floculation du latex dans les appareils et le retard des analyses, qui sont dues, pour partie, au transfert du latex. C'est pourquoi, les expériences sont préférablement suivies avec les capteurs in situ, où l'analyse est effectuée dans le réacteur. Cependant, ces capteurs, tels que l'infrarouge, l'ultrason et la spectroscopie Raman sont en phase de développement, et nous ne possédons pas encore de modèles complets liant ces mesures avec les propriétés du latex.

Le manque de capteurs en ligne qui donnent des mesures réelles des procédés est un problème fréquent dans plusieurs domaines. Dans les procédés de polymérisation en émulsion, ce manque est d'abord dû à la nature hétérogène et visqueuse du latex qui rend la mesure directe des propriétés du polymère souvent difficile. Ensuite, l'équipement d'un procédé avec plusieurs capteurs serait économiquement impossible. A cause du manque de capteurs, et du manque de modèles exacts des procédés, des efforts ont été faits dans le domaine de l'estimation logicielle des états, non mesurés expérimentalement, en se basant sur des mesures réelles et le modèle du procédé. Ces observateurs, ou estimateurs, ou encore capteurs logiciels, sont conçus à partir du modèle du procédé en utilisant les sorties réelles du procédé. Si le système est observable, l'observateur nous permettra d'obtenir des informations sur les états non mesurés du procédé. Les observateurs sont souvent utilisés pour le suivi des procédés, mais sont également très utiles pour le filtrage, la détection de panne et le contrôle des procédés.

Les méthodes d'estimation et de contrôle linéaire ont souvent été appliquées dans le domaine de la polymérisation en émulsion, et ce malgré la nonlinéarité des modèles représentant ces procédés. Ceci est dû premièrement à la difficulté de manipuler les outils non linéaires, au temps nécessaire à l'ordinateur pour résoudre ces observateurs et au fait que les observateurs non linéaires proposés dans la littérature étaient souvent limités à un groupe de systèmes non linéaires. Ces sujets ne posent aucune difficulté aujourd'hui, avec le développement de la théorie non linéaire, et l'évolution de la rapidité et de la capacité des ordinateurs.

L'objectif de ce travail est le contrôle de la composition des polymères, tout en assurant une vitesse de réaction élevée, ainsi que la sécurité de l'opération. Puisque les modèles représentant ce procédé sont nonlinéaires, nous allons utiliser des méthodes d'estimation et de contrôle nonlinéaires adaptées au procédé.

La stratégie d'estimation est constituée de trois parties. Dans la première partie, nous allons développer un capteur qui fournit des informations précises et rapides sur le procédé. La deuxième partie est constituée de l'estimation de la composition du polymère lors des procédés de co- et terpolymérisations en émulsion. La dernière étape est la construction de lois de commande adéquates qui nous permettent d'obtenir la composition et la vitesse de réaction désirées.

Dans le premier chapitre, une introduction générale du sujet ainsi que la stratégie de recherche sont proposées. Le deuxième chapitre contient les théories d'estimation et de contrôle nonlinéaires que nous allons utiliser tout au long de ce travail.

Le troisième chapitre traite des capteurs en ligne pour les procédés de polymérisation en émulsion. D'après certains critères , nous choisissons d'utiliser la calorimétrie pour suivre le procédé. Cependant, ce capteur ne nous donne pas directement une mesure de la vitesse de la réaction, car plusieurs paramètres dans le bilan thermique restent inconnus. Pour contourner ce problème, nous allons utiliser une méthode d'optimisation de la conversion globale du monomère, en corrigeant les paramètres inconnus. Pour ce faire, les mesures de la température du réacteur, de la double enveloppe, et quelques mesures expérimentales de la conversion sont nécessaires.

Dans le quatrième chapitre nous utilisons les informations obtenues par calorimétrie, pour estimer la composition du polymère lors des procédé de copolymérisation. Nous traitons le cas d'un observateur nonlinéaire à grand gain qui tient compte de la réaction dans la phase aqueuse et un autre où on néglige l'effet de la phase aqueuse. Il s'avère que, pour les monomères étudiés, la composition du polymère n'est pas sensible à la réaction dans la phase aqueuse. Ce phénomène est peut être dû au fait que la plupart des radicaux sont dans les particules, surtout pour un taux de solide élevé. La deuxième raison est que les monomères utilisés ici sont seulement partiellement solubles dans l'eau, ce qui fait que la quantité de monomère dans les particules est plus importante que dans la phase aqueuse.

Dans le cinquième chapitre, un observateur nonlinéaire à grand gain est construit pour suivre la composition du polymère lors des procédés de terpolymérisation. Puisque le quatrième chapitre montre clairement que nous n'avons pas besoin de tenir compte de la phase aqueuse pour l'estimation de la composition, un modèle de monomères hydrophobes est choisi pour construire l'observateur.

Le chapitre 6 expose les lois de commande développées pour maintenir la composition de co- et de terpolymères sur une trajectoire prédéfinie. Des lois de commande nonlinéaires avec une linéarisation entrée-sortie sont utilisées. Dans ce chapitre, nous établissons un contrôleur local de la pompe, qui assure l'exécution des débits envoyés par la commande de la composition.

Dans le dernier chapitre nous évoquons le concept de maximisation de productivité. Notre objectif est de maintenir la composition à une valeur prédéfinie, et en même temps maximiser la vitesse de la réaction. Les variables de commande sont les débits d'ajout de monomères. La variable contrôlée est la concentration de monomère dans les particules. Cependant, pendant le contrôle de la concentration de monomère dans les particules il faut faire attention à ce que la chaleur produite par la réaction soit inférieure à la chaleur maximale que la double enveloppe est capable d'évacuer.

The potential for conjugated linoleic acid (CLA) incorporation into pressure-sensitive adhesive (PSA) formulations was evaluated. A series of free radical bulk copolymerizations of CLA/styrene (Sty) and CLA/butyl acrylate (BA) were designed to allow the estimation of reactivity ratios. Bulk terpolymerizations of CLA/Sty/BA were also evaluated before moving to emulsion terpolymerizations of CLA/Sty/BA. The polymers were characterized for composition, conversion, molecular weight and glass transition temperature while latexes were characterized for viscosity, particle size, tack, peel strength, and shear strength. All experiments were performed at 80oC and monitored with attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. While bulk experiments were monitored off-line, the emulsion experiments were monitored in-line. Absorbance peaks related to the monomers and polymer were tracked to provide conversion and polymer composition data using a multivariate calibration method. Off-line measurements using gravimetry and 1H-NMR spectroscopy were compared to the ATR-FTIR data and no significant differences were detected between the measurement methods. Pseudo-kinetic models, developed and validated with the copolymer experimental data, were used to estimate reactivity ratios. The copolymer pseudo-kinetic models were extended to a terpolymer pseudo-kinetic model and validated with experimental data. The pseudo-kinetic models incorporated the ability of oleic acid, a common impurity found in CLA, to trap electrons thus influencing the reaction kinetics significantly. The influence of terpolymer composition, chain transfer agent concentration, cross-linker concentration, molecular weight, viscosity and particle size on tack, peel strength and shear strength was investigated by using a constrained mixture design. The final forms of the resulting empirical models allowed the creation of 3D response surfaces for PSA performance optimization. The incorporation of 30 wt.% CLA into a practical PSA application suitable for the removable adhesives category was achieved.

L'objectif de cette thèse est de proposer des applications innovantes pour la polymérisation en émulsion et en mini-émulsion dans différents procédés : réacteur fermé parfaitement agité, semi-continu et continu. Des résultats similaires au réacteur fermé furent obtenus dans le réacteur tubulaire continu pour des taux de solides inférieurs à 30 % en poids. La polymérisation en mini-émulsion s'est alors révélée comme un candidat prometteur en vue d'éliminer les problèmes de démixtion rencontrés à des taux de solide plus important. Dans une étude préliminaire en réacteur fermé nous avons mis en évidence la nucléation complète des gouttelettes de monomères et leurs compartimentalisations. Des procédés de synthèse de latex à haut extrait sec et de viscosité faible avec un contrôle de la distribution des masses molaires ont été ainsi proposés. En mini-émulsion des réactions à taux de solides supérieurs à 30 % en poids ont été réalisées dans le réacteur tubulaire continu

Cyclodextrins (CD) are semi-natural oligosaccharides composed of a number of D-glucose units. They are produced from renewable resources, and have been found to be of catalytic effect for the emulsion polymerization of many monomers. Using monomers whose emulsion polymerization kinetics have been thoroughly studied, this research analyses the effect of CD on the entry and exit rate coefficients for the emulsion polymerization of styrene, and the entry and termination rate coefficients for the emulsion polymerization of MMA. Throughout the course of the work, CD was found to have a positive impact on the polymerization rate of styrene in a polystyrene latex stabilized with a cationic surfactant. Furthermore, the exit rate coefficient for this latex was found, via γ-relaxation experiments, to increase in proportion to the styrene solubility in water, exactly as predicted by theory. Of itself this would lead to a decrease in reaction rate. That there is still an overall increase in the reaction rate in the presence of CD is because of a quite strong effect on entry rate coefficients. Again, this is consistent with the prevailing theory for entry, that of Maxwell and Morrison, which says that increased aqueous phase solubility of monomer will lead to faster entry. Intriguingly, experiments done on a polystyrene latex stabilized with an anionic surfactant showed a different effect for CD: γ-relaxation experiments found very little effect of CD on exit rate, and chemically initiated experiments found the same for overall rate. This is consistent with CD having little effect on aqueous phase styrene solubility, which in fact is what direct measurements via UV-visible spectroscopy indicated. It is speculated that the anionic surfactant was successfully competing with styrene to occupy the CD cavities. On the other hand, measurements suggested that styrene successfully competes with cationic surfactant, which is consistent with kinetic results. Experiments of the above nature were then carried out with methyl methacrylate (MMA), a more water soluble monomer than styrene and one with emulsion polymerisation kinetics of a different nature (so-called pseudo-bulk). γ-relaxation experiments found no effect of CD on termination rate coefficients, exactly as one would expect given that termination is an intra-particle reaction whereas CD exists in the aqueous phase. However the same experiments also revealed an unexpected effect of CD on entry: the thermal entry rate coefficient was found to increase markedly in the presence of CD. It seems likely that this unusual effect stems from interaction of products of γ radiolysis with CD. Results for chemically-initiated polymerization of MMA were inconclusive. Under some conditions there was actually retardation in the presence of CD, which is actually consistent with measurements of MMA solubility in water, which suggested a slightly negative effect of CD. However it is hard to explain such a phenomenon. Further, under other conditions it was found that CD either had no effect on chemically-initiated rate or could even increase it slightly. The only safe conclusion at this stage is that CD has no major effect on MMA kinetics, which arguably is consistent with MMA being relatively water soluble: intuitively one would expect that CD is most useful (‘catalytic’) for the EP of monomers of low solubility.

Thesis (MScEng)--Stellenbosch University, 2000.
ENGLISH ABSTRACT: ABSTRACT: A new emulsion (code name: NW 120) has been developed by Plascon on laboratory scale, for application in the paint industry. It is an environmentally friendly emulsion in which no coalescent solvent is used. It also has a core-shell morphology. Research was undertaken to scale-up (industrialize) the emulsion polymerization of NW 120. The use of a suitable pilot plant was investigated. An available bench-scale pilot plant (RCl, Mettler Toledo) was found to be very expensive. The reactors were very small (R:1.8 l) and the reactor set-ups (reactor, baffies and stirrer configuration) were not similar to the industrial size reactors used by Plascon. A fully computer controlled bench-scale pilot plant was subsequently designed and built at a fraction of the cost of the commercially available set-up. The reactor (5 I) was a scale-down replica (geometrically similar) of the industrial size reactors used by Plascon. The reactor was designed to also serve as a calorimeter. Very good control was achieved over the reaction temperature and addition rates of the monomers and catalyst. Heat loss and heat capacity models were derived for a variation in the reaction temperature between 82.5 - 87.5 °c in order to perform accurate energy balances (calorimeter) around the reactor. The accuracy of the calorimeter was verified at a reaction temperature of 85°C, by measuring the heat that evolved when a sodium hydroxide solution was diluted with water. The accuracy of the calorimeter was found to be extremely good. The pilot plant was commissioned with an industrially manufactured emulsion (code name: AE 446), well known to Plascon. The results obtained in the pilot plant reactor were very similar to those obtained for the full-scale manufacturing of AE 446. It was determined that if geometrical similarity between the pilot plant reactor and the industrial size reactor is preserved and if the correct process conditions (stirring speed, reaction temperature and addition rates of the monomers/catalyst) are maintained, then the direct scale-up of the production ofNW 120, from bench-scale to full-scale, would be possible. The reaction conditions were varied over a wide range, in order to find the optimum process conditions. The stirring speed was varied between 150 - 550 rpm. Shear sensitivity was observed at stirring speeds of 450 rpm and higher. The measured physical properties at 550 rpm were found to be unacceptable. The optimum stirring speed for the desired particle size and viscosity was found to lie between 150 rpm and 250 rpm. The reaction temperature was varied between 70 and 90 DC. The optimum reaction temperature was found to lie between 80 and 90 De. It was possible to successfully reduce the monomer addition time, and hence the reaction times, by increasing the addition rate of the monomers/catalyst, from 4 h to 2 ~ h. The method developed by Klein et al. (1996), for the scale-up of the stirring speed of emulsion polymerization reactions was used to determine the equivalent fullscale stirring speed. The scale-up of NW 120 was subsequently conducted at 85 DC, at a stirring speed of 35 rpm and the monomers/catalyst were added over a period of 4 h. The use of reduced reaction times were not considered in the first scale-up run since at that stage it was not clear whether the heat removal capability of the industrial size reactor would be adequate to cope with the increase in the evolved heat, associated with an increase in the addition rates of the monomers/catalyst. Very good results were obtained. The measured physical properties of NW 120 produced in the industrial size reactor were found to be almost exactly the same as in the pilot plant reactor.
AFRIKAANSE OPSOMMING: 'n Nuwe emulsie (kode naam NW 120) is deur Plascon op laboratorium skaal ontwikkel, vir die gebruik in die verfbedryf. Dit is 'n omgewingsvriendelike produk en geen oplosmiddels word gebruik vir die filmvormingsproses nie. Hierdie projek handeloor die opskalering (industrialisering) van die produksie van NW 120. Die gebruik van 'n geskikte loodsaanleg is eers ondersoek. Daar is gevind dat die beskikbare laboratorium skaalloodsaanleg (RCl, Mettler Toledo) baie duur was. Die reaktore is baie klein (:::::1.81). Die reaktoropstellings (reaktor, keerplate en roerder-konfigurasie) is ook nie in ooreenstemming met die industriële grootte reaktore wat deur Plascon gebruik word nie. 'n Ten volle rekenaarbeheerde loodsaanleg is ontwerp en gebou teen 'n breuk van die koste van soortgelyke kommersieel beskikbare opstellings. Die reaktor (5 I) is 'n skaalmodel (geometries gelykvormig) van die industriële grootte reaktore wat deur Plascon gebruik word. Die reaktor word ook aangewend as 'n kalorimeter. Baie goeie beheer oor die reaktortemperatuur, sowel as die toevoertempo's van die monomere en die katalis is verkry. Hitteverlies en hittekapasiteits modelle is afgelei vir variasies in die reaktortemperatuur tussen 82.5 - 87.5 °c om dit moontlik te maak om akkurate energiebalanse te kan opstel (kalorimeter). Die akkuraatheid van die kalorimeter is getoets by 85°C, deur die verdunningswarmte van 'n natriumhidroksiedoplossing te meet. Daar is gevind dat die kalorimeter baie akkuraat is. 'n Industrieel vervaardigde (plaseon) emulsie (kode naam: AB 446) is gebruik om die loodsaanleg in bedryf te stel. Die resultate wat in die loodsaanleg verkry is, was ongeveer dieselfde as die resultate wat in die industriële reaktore verkry word. Hierdie resultate toon dat indien die reaktore geometries gelykvormig is en indien die regte prosestoestande (roerspoed, reaksietemperatuur en toevoertempo's van die monomere/katalis) gebruik word, dit moontlik sou wees om NW 120 direk op te skaal van loodsaanleg tot volskaal. Die reaksietoestande is gevaneer oor 'n wye bereik om die optimum prosestoestande te probeer verkry. Die roerspoed is gevarieer tussen 150 - 550 opm. Daar is gevind dat die emulsie sleur sensitief is bokant 'n roerspoed van 450 opm. Die gemete fisiese eienskappe by 'n roerspoed van 550 opm was onaanvaarbaar. Die optimum roerspoed in terme van partikelgrootte en viskositeit lê tussen 150 en 250 opm. Die reaksietemperatuur is gevarieer tussen 90 - 70°C. Die optimum temperatuur lê tussen 90 - 80 °C. Dit was moontlik om die monomeer-toevoertyd, m.a.w die reaksietyd, te verminder deur die toevoertempo van die monomere/katalis te verhoog, van 4 tot 2 ~ uur. Die metode wat deur Klein et al. (1996) ontwikkel is vir die opskalering van die roerspoed van 'n emulsiepolimerisasie reaksie is gebruik om die ekwivalente roerspoed vir die opskalering te verkry. Die opskalering van NW 120 is uitgevoer by 'n reaksietemperatuur van 85°C en 'n roerspoed van 35 opm. Die monomere/katalis is toegevoer oor 'n tydperk van 4 uur. Die verkorte reaksietyd is nie oorweeg vir die opskaleringslopie nie omdat dit nog nie seker was of die hitteverwydering van die industriële reaktor effektief genoeg sou wees om die verhoging in die reaksiewarmte-ontwikkeling, wat geassosieer word met 'n verhoging in die toevoertempo van die monomere/katalis, te kan verwyder nie. Baie goeie resultate is verkry. Die gemete fisiese eienskappe van NW 120 wat verkry is in die industriële reaktor was ongeveer dieselfde as dié wat verkry is op die loodsaanleg.

Thesis (PhD)--Stellenbosch University, 2004.
ENGLISH ABSTRACT: The study presented in this dissertation had as primary aim to develop pathways to heterogeneous aqueous polymerizations that had living characteristics. To this end, the reversible addition fragmentation chain transfer (RAFT) process was investigated in predispersed and ab initio emulsions as well as homogeneous media. The synthesis of RAFT agents was carried out. The compounds prepared provided varied behaviour in reaction. In situ IH nuclear magnetic resonance (NMR) increased understanding of homogeneous RAFT mediated polymerizations. The early behaviour of RAFT mediated polymerizations led to the definition of initialization; a period before pre-equilibrium in a polymerization where degenerate behaviour occurs. Stable miniemulsion preparation methods were developed that provided living polymer latexes using high surfactant concentrations. The effect of surfactant concentration on particle size and latex stability was investigated. Living polymer characteristics were shown by the use of size exclusion chromatography, and 2- dimensional chromatography conclusively showed block polymer formation. In situ NMR spectroscopy of emulsions in deuterated water was used to provide evidence on the role of initiator solubility in polymerization. Secondary nucleation in high surfactant concentration miniemulsions systems was investigated using both particle size and molar mass analysis techniques and a means of eliminating secondary particle nulceation was shown through the use of aqueous phase radical traps. The role of the RAFT agent used in the polymerization was shown to be significant in determining the extent to which multiple polymer distributions formed in the polymerization in that radical exit from particles was affected. Finally, a new form of emulsion polymerization, which has been termed proto-seeded emulsion, has been developed. The proto-seed latex is formed by using a monomer whose polymer has chain length dependent water solubility. This process allows ab initio RAFT mediated emulsion polymerization to be conducted successfully without transport of RAFT agents in heterogeneous media.
AFRIKAANSE OPSOMMING: Die primerê doel in hierdie dissertasie is die ontwikkeling van roetes na heterogene water-gebaseerde polimerisasies met lewende eienskappe. Om hierdie doel te bereik is die omkeerbare addisie fragmentasie ketting oordrag proses (eng reversible addition fragmentation chain transfer (RAFT)) ondersoek in vooraf verspreide en direkte emulsies sowel as homogene media. Die sintese van RAFT agente is uitgevoer. Die verbindings wat voorberei is het verskillende einskappe in reaksies getoon. In situ IH kern magnetiese resonansie (KMR) het die kennis en begrip van homogene RAFT polimerisasies uitgebrei. Die vroeë gedrag van RAFT polimerisasies het tot die definisie van inisialisasie gelei; 'n periode voor die pre-ekwilibrium in 'n polimerisasie waartydens "degenerate" gedrag plaasvind. Stabiele miniemulsie voorbereidings metodes is ontwikkel wat lewende polimeer latekse verskaf het met gebruik van hoë seep konsentrasies. Die effek van seep konsentrasie op partikel grootte en lateks stabilitiet is ondersoek. Lewende polimeer eienskappe is bewys deur gebruik te maak van grootte-uitsluiting vloeistof chromatografie, en 2-dimensionele chromatografie het duidelik blok-polimeer vorming gewys. In situ KMR spektroskopie van emulsies in gedeutereerde water is gebruik om bewys te lewer van die rol van initieerder-oplosbaarheid in polimerisasie. Sekondêre nukleasie in hoë seep konsentrasie miniemuisie sisteme is ondersoek met die gebruik van beide partikel grootte sowel as molêre massa analise tegnieke. 'n Metode om sekondêre partikels te verhoed is verskaf deur gebruik te maak van waterfase radikaal lokvalle. Die rol van die RAFT agent in die polimeerisasie is beduidend in die graad van vorming van meer as een polimeer distribusie in die sin dat radikal uitgang van partikels beinvloed was. Ten slotte is 'n nuwe vorm van emulsie polimeerisasie ontwikkel wat proto-gesaaide emulsie genoem is. Die proto-gesaaide lateks is gevorm deur gebruik te maak van 'n monomeer waarvan die polimeer water-oplosbaarheid afhanklik is van die kettinglengte. Die proses laat ab initio RAFT emulsie polimerisasie toe om suksesvol uitgevoer te word sonder die vervoer van RAFT agente in heterogene media.

A polimerização em emulsão de estireno em um microrreator Syrris de 250 µL com misturador estático junção \"T\" foi estudada em duas etapas. Primeiro somente a fluidodinâmica deste dispositivo não convencional foi avaliada, depois, foi desenvolvida a reação de polimerização de forma a observar como este fator influencia no sistema. Os experimentos foram realizados procurando se atingir maiores conversões, mas mantendo a estabilidade da emulsão. Foi um trabalho exploratório, portanto se assemelha mais a um processo de evolução (evolutionary process). Foram verificados a partir de qual relação das vazões dos dois fluidos ocorre a formação de gotas, e que com o aumento da vazão da fase contínua, aquosa (Qc), mantendo constante a vazão da fase dispersa (Qd), foi verificado uma diminuição do diâmetro das gotas e um regime de fluxo laminar. Posteriormente, realizou-se a polimerização em emulsão do estireno no microrreator, porém com restrições para altas vazões. Os parâmetros de processo testados foram a proporção Qc e Qd, a temperatura e a concentração do iniciador para então verificar o efeito que a variação destas ocasionam na conversão de monômero, no diâmetro e número de partículas e nas massas moleculares médias. A polimerização foi feita para soma das vazões Qc e Qd da ordem de 100 µ L/min, com 15% de monômero na formulação e com o maior tempo de residência possível de 2,5 minutos. Para maiores concentrações de monômero, acima de 15% foi verificado entupimento do canal do microrreator. A taxa de conversão de monômero aumentou com o aumento da temperatura e com o aumento da concentração do iniciador, mas o maior valor atingido foi de apenas 37% devido ao baixo tempo de residência. Nos casos de maiores taxas de conversão, as massas moleculares obtidas foram as menores conforme o esperado pela teoria. Finalmente, os índices de polidispersão (PDI), obtidos foram da ordem de 2,5 a 3,5.
The emulsion polymerization of styrene in a microreactor Syrris 250 µL with static mixer junction \"T\" was studied in two steps. First, only the fluidynamics of this nonconventional device was evaluated, after the polymerization reaction was developed in order to observe how this factor influencing the system. The experiments were performed seeking to achieve higher conversions, keeping the stability of the emulsion. It was an exploratory work therefore is more like an evolutionary process. The ratio of two-phase flow rates was analyzed from which of them occurs droplet formation. The flow rate of dispersed phase (Qd) was kept constant and the continuous phase (Qc), was increased. It can be observed the decreasing of droplet diameter and a laminar flow regime. Later, it was carried out emulsion polymerization of styrene in the microreactor with restrictions for high flow rates. The process parameters were analyzed: the ratio Qc/Qd, the temperature and initiator concentration and then determine the effect that these variations cause the monomer conversion, the diameter, number of particles and the average molecular weight. The polymerization occurred to the sum of the flow rates Qc and Qd of around 100 µ L/min with 15% monomer in the formulation with the highest residence time of 2,5 minutes. For higher concentrations of monomer, above 15% was observed clogging in the microreactor channel. The monomer conversion rate raised with increasing temperature and with the concentration of initiator, but the largest value achieved was only 37% due to the low residence time. In this case, the molecular weights obtained were smaller as expected by theory. Finally, the polydispersity indexes obtained were around 2.5 to 3.5.

For more than 70 years, understanding of the mechanism of particle nucleation in emulsion polymerization has been one of the most challenging issues in heterophase polymerization research. Within this work a comprehensive experimental study of particle nucleation in emulsion polymerization of styrene at 70 °C and variety of conditions has been performed. To follow the onset of nucleation, on-line conductivity measurements were applied. This technique is highly sensitive to the mobility of conducting species and hence, it can be employed to follow aggregation processes leading to particle formation. On the other hand, by recording the optical transmission (turbidity) of the reaction mixture particle growth was followed. Complementary to the on-line investigations, off-line characterizations of the particle morphology and the molecular weight have been performed. The aim was to achieve a better insight in the processes taking place after starting the reaction via particle nucleation until formation of colloidally stable latex particles. With this experimental protocol the initial period of styrene emulsion polymerization in the absence as well as in the presence of various surfactants (concentrations above and below the critical micellization concentration) and also in the presence of seed particles has been investigated. Ionic and non-ionic initiators (hydrophilic and hydrophobic types) have been applied to start the polymerizations. Following the above algorithm, experimental evidence has been obtained showing the possibility of performing surfactant-free emulsion polymerization of styrene with oil-soluble initiators. The duration of the pre-nucleation period (that is the time between starting the polymerization and nucleation) can be precisely adjusted with the initiator hydrophobicity, the equilibration time of styrene in water, and the surfactant concentration. Spontaneous emulsification of monomer in water, as soon as both phases are brought into contact, is a key factor to explain the experimental results. The equilibration time of monomer in water as well as the type and concentration of other materials in water (surfactants, seed particles, etc.) control the formation rate and the size of the emulsified droplets and thus, have a strong influence on the particle nucleation and the particle morphology. One of the main tasks was to investigate the effect of surfactant molecules and especially micelles on the nucleation mechanism. Experimental results revealed that in the presence of emulsifier micelles the conductivity pattern does not change essentially. This means that the presence of emulsifiers does not change the mechanism of particle formation qualitatively. However, surfactants assist in the nucleation process as they lower the activation free energy of particle formation. Contrary, seed particles influence particle nucleation, substantially. In the presence of seed particles above a critical volume fraction the formation of new particles can be suppressed. However, micelles and seed particles as absorbers exhibit a common behavior under conditions where monomer equilibration is not allowed. Results prove that the nucleation mechanism comprises the initiation of water soluble oligomers in the aqueous phase followed by their aggregation. The process is heterogeneous in nature due to the presence of monomer droplets.
Polymere dominieren unsere Welt. Die natürlich vorkommenden Polymeren, wie Proteine, Polynukleotide, und Polysaccharide, sind nötig um das Leben zu erhalten. Ebenso wichtig sind die kommerziell erhältlichen Makromoleküle. Beides sind Bausteine, um Materialien zu konstruieren, welche man in beiden Welten finden kann- der natürlichen und der „Mensch-gemachten“ Welt. Unter den verschiedenen Polymerisationsmethoden hat sich die Emulsions-polymerisation zu einem weit verbreiteten Prozess entwickelt. Die Emulsionspolymerisation ist ein einzigartiger Polymerisationsprozess, bei dem ein Monomer oder ein Gemisch von Monomeren in einem wässrigen Medium polymerisiert wird. Dabei entsteht eine Dispersion von Polymeren, welche auch als Latex bezeichnet wird. Derzeit werden mehrere Millionen Tonnen von synthetischen Latices mit Hilfe der Emulsionspolymerisation hergestellt. Diese finden zum Beispiel Verwendung als synthetische Gummi, Latexschaum, Latexfarben, Papierbeschichtungen und Klebstoffen. Außerdem findet man sie auch bei Spezialanwendungen, wie Diagnosetests, Pharmakotherapien und chromatographischen Trennmethoden. Trotz der Vielzahl von industriellen Anwendungen, sollten all jenen, die sich mit Emulsionspolymerisation beschäftigen, den wissenschaftlichen und technologischen Herausforderungen, die sich stellen, bewusst sein. Die wichtigsten Fragen beim Umgang mit der Emulsionspolymerisation beinhalten das Verständnis des Prozesses der Partikelbildung und des Partikelwachstums. Die vorliegende Dissertation beschäftigt sich mit der Frage der Keimbildungs-etappe in Emulsionspolymerisationen. Die Untersuchungen wurden mit Hilfe eines on-line Leitfähigkeitsmessverfahren sowie einigen off-line analytischen Experimenten durchgeführt. Basierend auf den klaren experimentellen Daten, wurde ein besserer Einblick in die tatsächlichen Zustände des Polymerisationssystems, von der Zeit der neu geboren Kerne bis zu endgültig stabilisierten Teilchen, gewonnen.

Un système consistant d'une simulation de mécanique des fluides numérique (MFN) couplée à un modèle de bilan de population (PBM) est développé afin d'étudier l'effet des paramètres variés sur la performance d'un procédé de polymérisation en émulsion qui conduit à la peoduction des particules de polymère dans un milieu aqueux continu.Comme une grande gamme des produits polymériques, des latexes sont les « produits par processus » (products-by-process), et leurs propriétés sont déterminés pendant la polymérisation. LA distribution de la taille des particules (PSD) est une des plus importants paramètres qui influence la qualité finale de latex. La modélisation d'évolution du PSD est généralement réalisée par l'addition un ensemble des PBEs au modèle cinétique. Le PBE fournit un moyen d'étudier la contribution des différents phénomènes dans l'évolution du PSD, comme la nucléation, la croissance des particules par la polymérisation, et la coagulation des particules à cause du mouvement brownien ou le mouvement du fluide (la coagulation Perikinetic et Orthokinetic, respectivement).Afin d'évaluer l'impact du mélange non homogène et les paramètres physiques du système sur l'évolution du PSD du latex, la simulation transitoire d'écoulement à été réalisé avec l'aide d'un progiciel commercial de MFN (Fluent® 15.0) pour munir dans chaque pas du temps, les concentrations locales des espèces ioniques (pour déterminer le taux de la coagulation Perikinetic modelé par le modèle de DLVO) ainsi que certains paramètres hydrodynamiques comme le taux de dissipation de la turbulence et le taux de cisaillement (afin de déterminer le taux de la coagulation Orthokinetic). Cette information est appliquée simultanément par le module complémentaire de PBM dans Fluent pour calculer le PSD pour le prochain pas du temps ; ainsi, un couplage complet entre le MFN et le PBM est assuré
A framework, consisting of a computational fluid dynamics (CFD) simulation model coupled to a population balance model (PBM) is developed to study the effect of various parameters on the performance of an emulsion polymerization process which leads to the production of a fine dispersion of polymer particles in a continuous aqueous medium.Like most polymer products, latexes are “products-by-process”, whose main properties are determined during polymerization. One of the main parameters influencing the final quality of the latexes is the particle size distribution (PSD). Modeling the evolution of PSD is usually accomplished through the addition of a set of PBEs to the kinetic model. PBE provides a means of considering the contribution of different phenomena in the PSD evolution, being nucleation, growth of polymer particles by polymerization, and coagulation of particles due to brownian or fluid motion (Perikinetic and Orthokinetic coagulation, respectively).To assess the impact of nonhomogeneous mixing and physical parameters of the system on the evolution of the latex PSD, the transient simulation of flow was performed with the aid of a commercial CFD Package (Fluent® 15.0) to provide in each time step, the local concentrations of ionic species (to determine the rate of perikinetic coagulation modeled by DLVO model) and certain hydrodynamic parameters such as turbulence dissipation rate and shear rate (to determine the rate of orthokinetic coagulation). This information is applied simultaneously by the PBE add-on module of Fluent to calculate the PSD for the next time step; thus a complete coupling between CFD and PBM is assured