Ce travail de recherche a pour objet l'application du procédé de polymérisation en miniémulsion de l'acétate de vinyle pour l'encapsulation de principes actifs à usage cosmétique. Ce procédé permet d'obtenir des latex à haut taux de solide et contenant une forte proportion de molécules actives. Ce travail est divisé en deux partie : l) la formation de nanoparticules et l'étude de l'incorporation de différents principes actifs, 2) la détermination de la morphologie des particules. Dans un premier temps, nous avons optimisé le procédé de polymérisation radicalaire en miniémulsion de l'acétate de vinyle. La composante hydrophobe indispensable à la bonne stabilité de la miniémulsion est assurée par le principe actif lui-même. Nous avons obtenu des latex stables pendant six mois à trois températures différentes : 4°C, 20°C et 40 °C et ce pour différents principes actifs. Dans un deuxième temps, nous avons étudié la morphologie interne des nanoparticules. Une étude prédictive basée sur les mesures des tensions superficielles et interfaciales entre les différents composés de la miniémulsion indiquent une encapsulation partielle du principe actif par le polymère. Bien que difficiles à mener sur les latex de PAcV, les observations par microscopie électronique semblent confirment cette tendance. Un changement de tensioactif et l'addition de monomère lors de la réaction de polymérisation pourraient favoriser la formation de nanocapsules / The aim of this work is the encapsulation of active ingredients by vinyl acetate miniemulsion polymerization for cosmetic use. This process allows to obtain latexes with high solid content and containing high amount of active molecule. This work is divided into two parts: 1) nanoparticles formation by miniemulsion polymerization and incorporation of different active principles 2) determination of the nanoparticles morphology. At first, the process of radical miniemulsion polymerization in for vinyl acetate is optimized. The hydrophobe compound, which is essential for the miniemulsion stability, is ensured by the active principle itself. We obtained several stable latexes with different active molecules at three different temperatures: 277 °K, 293°K and 313°K during six months. In the second part of this work, we studied the internal morphology of nanoparticles. A predictive study, based on the surface and the interfacial tension measurements between the different compounds of miniemulsion has been undertaken, which indicates a partial engulfing of the active principle by the polymer. Although the observation of PVAc lattices by electronic microscopy may be questionable, these studies seem to confirm this trend. The change of the surfactant and the monomer addition during the reaction of polymerization can favour the formation of nanocapsules

No description available.

The stable free radical polymerization methodology for production of controlled macromolecules was investigated using a novel monomer, 2-vinylnaphthalene. Initial polymerizations resulted in molecular weight distributions typical of conventional free radical polymerization techniques (>2.0). Manipulation of the initiator concentration and the molar ratio of initiator to nitroxide demonstrated no significant control over the resulting polymer products. Analysis of the polymerization kinetics for a 2-vinylnaphthalene polymerization performed in the presence and absence of the free radical initiator revealed identical monomer consumption profiles as well as pseudo first order kinetics indicating a significant degree of the thermal polymerization was occurring at the polymerization temperature (130°C). Comparison of the thermal polymerization propensity of 2-vinylnaphthalene and styrene revealed an increased tendency for 2-vinylnapthahlene to undergo thermal polymerization. Styrene is considered highly active in its propensity to thermally polymerize. However, an Arhenius analysis using in situ FTIR was employed to determine the activation energy for the thermal polymerization of styrene and 2-vinylnaphthalene. The 2-vinylnaphthalene activation energy for thermal polymerization was determined for the first time to be almost 30 kJ/mol less than styrene. A novel modified Mayo mechanism was proposed for the 2-vinylnaphthalene thermal initiation mechanism. Moreover, this thermal initiation was employed to initiate nitroxide mediated polymerizations of styrene. This first use of a 2-vinylnaphthalene initiating system resulted in polystyrene with a large macrocyclic initiating fragment. The presence of the initiating moiety was studied using both UV-Vis spectroscopy and 1H NMR spectroscopy. The extension of stable free radical polymerization to the acrylate monomer family was examined using a novel nitroxide mediator, N-tert-butyl-N-[1-diethylphosphono-(2,2-dimethylpropyl)] nitroxide (DEPN). The synthesis of DEPN was monitored using in situ FTIR spectroscopy to determine optimum reaction conditions. The purified nitroxide was subsequently employed in the synthesis of various block and random acrylate copolymers. The production of a unique amphiphilic block copolymer consisting of acrylic sequences was achieved. Poly(t-butyl acrylate-b-2ethylhexyl acrylate-b-t-butyl acrylate) was synthesized using the SFRP process. The t-butyl functionalities were subsequently removed in a post-polymerization acid catalyzed hydrolysis. The effect of steric bulk and electronic factors on the resulting SFRP process was also investigated and revealed similar polymerization kinetics for various alkyl acrylates. However, addition of a hydroxyl containing monomer, 2-hydroxyethyl acrylate, resulted in an increase in the polymerization rate up to 2 times. The rate enhancement was attributed to hydrogen bonding effects and this was confirmed using the unprecedented addition of dodecanol, which also demonstrated a significant rate enhancement. Block copolymers were also achieved using a novel difunctional nitroxide synthesized from 4-hydroxy TEMPO and 1,6-hexamethylene diisocyanate. The identity of the nitroxide was confirmed using mass spectrometry and 1H NMR. The dinitroxide was used in the polymerization of styrene and subsequently used to produce symmetric ABA triblock copolymers with t-butyl styrene using a unique two-step polymerization route. In addition, the dinitroxide demonstrated an increased tendency for decomposition due to the complex mediation equilibrium. The decomposition was studied using GPC to evaluate the decomposition effects on the polymerization. Results of the research efforts presented herein are written as individual research reports with contributing authors and pertinent literature reviews presented at the beginning of each chapter. / Ph. D.

Thesis (DSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Examples of the use of NMR spectroscopy in the study of radical polymerization processes have been described. The studies presented have made a significant contribution to the understanding of the fundamental mechanistic processes in these polymerization systems. It is pointed out that NMR in conventional radical polymerization is of limited use due to the concurrent occurrence of all elementary reactions (initiation, propagation and termination). Conversely, for living radical polymerization, NMR has great value. In that case, the elementary reactions are somewhat more restricted to specific times of the polymerization process. This allows for example the detailed study of the early stages of chain growth in Reversible Addition-­‐Fragmentation Chain Transfer (RAFT) mediated polymerization. Two different studies are described. The first is related to the early stages of RAFT-­‐mediated polymerization. A process for which we coined the name initialization was studied via in situ 1H NMR spectroscopy. It is shown that in many cases, there is a selective reaction that converts the original RAFT agent into its single monomer adduct. A few different examples and their mechanistic interpretation are discussed. It is also shown that NMR spectroscopy can be a valuable tool for the assessment of a RAFT agent in conjunction with a specific monomer and polymerization conditions. In the second study, 15N NMR, 31P NMR and 1H NMR are used for two different types of experiments. The first is a conventional radical copolymerization in which the growing chains are trapped by a 15N labeled nitroxide to yield a stable product. In the second experiment, a similar copolymerization is conducted under nitroxide-­‐mediated conditions. The nitroxide of choice contains phosphorous, which enables the quantification of the terminal monomer in the dormant chains. Each of the experiments individually provides interesting information on conventional radical copolymerization and nitroxide-­‐mediated copolymerization, respectively. Combination of the experimental data reveals an interesting discrepancy in the ratio of terminal monomer units in active chains and dormant chains. Although not unexpected, this result is interesting and useful from a mechanistic as well as a synthetic point of view. In terms of future perspectives, it is expected that the advanced analytical techniques as described here will remain crucial in polymer science. Present developments in radical polymerization, such as investigations into monomer sequence control, rely on accurate knowledge of kinetic and mechanistic details of elementary reactions. It is expected that such detailed studies will be a main challenge for the next decade of polymer research. / AFRIKAANSE OPSOMMING: Voorbeelde van die gebruik van KMR-­‐spektroskopie in die studie van radikaalpolimerisasies word beskryf. Hierdie studies het ʼn beduidende bydrae gelewer tot die verstaan van die fundamentele meganistiese prosesse in hierdie polimerisasiesisteme. Dit het daarop gewys dat KMR beperkte gebruike het in konvensionele radikaalpolimerisasies as gevolg van die gelyktydige voorkoms van alle basiese reaksies (afsetting, voortsetting en beëindiging). Aan die anderkant het KMR groot waarde vir lewende radikaalpolimerisasie. In hierdie geval is die elementêre reaksies ietwat meer beperk tot spesifieke tye van die polimerisasieproses. Gedetailleerde studies kan byvoorbeeld van die vroeë stadiums van die kettinggroei in Omkeerbare Addisie-­‐Fragmentasie-­‐ KettingOordrag (OAFO)-­‐bemiddelde polimerisasie gedoen word. Twee verskillende studies is beskryf. Die eerste het betrekking op die vroeë stadiums van die OAFO-­‐bemiddelde polimerisasie. 'n Proses wat “inisialisering” genoem is, is bestudeer deur middel van in situ 1H KMR-­‐spektroskopie. Dit is bewys dat daar in baie gevalle 'n selektiewe reaksie is wat die oorspronklike OAFO-­‐agent in sy enkelmonomeeradduk verander voor polimerisasie. 'n Paar ander voorbeelde en hul meganistiese interpretasie is bespreek. Dit is ook bewys dat KMR-­‐spektroskopie 'n waardevolle hulpmiddel kan wees vir die assessering van 'n OAFO-­‐agent in samewerking met 'n spesifieke monomeer en polimerisasie toestande. In die tweede studie is 15N KMR, 31P KMR en 1H KMR gebruik vir twee verskillende tipes van die eksperiment. Die eerste is 'n konvensionele radikaalkopolimerisasie waarin die groeiende kettings vasgevang word deur 'n 15N-­‐gemerkte nitroksied om 'n stabiele produk te lewer. In die tweede eksperiment is 'n soortgelyke kopolimerisasie gedoen onder nitroksied-­‐ bemiddelde toestande. Die gekose nitroksied bevat fosfor wat die kwantifisering van die terminale monomeer in die dormante kettings moontlik maak. Elkeen van die individuele eksperimente lewer interessante inligting oor konvensionele radikale kopolimerisasie en nitroksied-­‐bemiddelde kopolimerisasie, onderskeidelik. ʼn Kombinasie van die eksperimentele data toon 'n interessante verskil aan in die verhouding van die terminale monomeereenhede in die aktiewe en sluimerende kettings. Alhoewel dit nie onverwags is nie, is die resultate interessant en van waarde vanuit 'n meganistiese-­‐ sowel as 'n sintetiese oogpunt. In terme van toekomstige perspektiewe word daar verwag dat gevorderde analitiese tegnieke soos hier beskryf, belangrik sal bly in polimeerwetenskap. Huidige ontwikkelinge in radikaalpolimerisasie, soos ondersoeke na die beheer van monomeervolgorde, maak staat op akkurate kennis van kinetiese en meganistiese besonderhede van die basiese reaksies. Daar word verwag dat sulke gedetailleerde studies ʼn uitdaging sal bied vir die volgende dekade van polimeernavorsing.

Diese Arbeit gibt neue Einblicke in die kinetischen und mechanistischen Aspekte der konventionellen radikalischen und der Reversible-Addition–Fragmentation-chain-Transfer- (RAFT-)Polymerisation von der Oberfläche von Silica-Nanopartikeln. Die Terminierungskinetik der oberflächeninitiierten Polymerisation von n-Butylmethacrylat (n-BMA) wurde mit Hilfe der Single-pulse–pulsed-laser-Polymerisation (SP–PLP) in Kombination mit der Elektronenspinresonanzspektroskopie (ESR-Spektroskopie) analysiert. Die Polymerisation wurde dabei durch den neu entwickelten oberflächengebundenen Photoinitiator 2,2-Dimethoxy-2-phenyl-1-(2-(2-(trimethoxysilyl)-ethyl)phenyl)-1-on (DMPTS) initiiert. Die erhaltenen Geschwindigkeitskoeffizienten der Terminierung kt, die ausschließlich der Terminierungsreaktion zwischen zwei oberflächengebundenen Radikalen zugeordnet werden konnten, waren signifikant kleiner als die Literaturwerte für das entsprechende homogene Polymerisationssystem. Erstaunlicherweise konnte außerdem keine Kettenlängenabhängigkeit von kt gefunden werden. Dies zusammen mit der Tatsache, dass bei temperaturabhängigen Untersuchungen eine Aktivierungsenergie für kt gefunden wurde, die in exzellenter Übereinstimmung mit der des Propagationsgeschwindigkeitskoeffizienten von n-BMA ist, lässt das Bild einer reaktionsdiffusionskontrollierten Terminierung oberflächengebundener Makroradikale entstehen. Die Entwicklung des oberflächengebundenen Photoinitiators DMPTS erlaubte weiterhin neue Einblicke in die Propagationskinetik – insbesondere deren Temperaturabhängigkeit betreffend – oberflächengebundener Makroradikale. Mittels der PLP von n-BMA in Kombination mit der Größenausschlusschromatographie (engl. size-exclusion chromatography, SEC) wurden Werte für den Geschwindigkeitskoeffizienten der Propagation kp und die entsprechende Aktivierungsenergie ermittelt, die exzellent mit den Daten der International Union of Pure and Applied Chemistry (IUPAC) für die Polymerisation von n-BMA in homogenem Reaktionsmedium übereinstimmen, sodass kein Einfluss der Oberflächenverankerung der Makroradikale auf die Propagationskinetik ersichtlich ist. Weiterhin wurde die Kinetik der RAFT-Polymerisation von n-Butylacrylat (BA) von Oberflächen bei –40 °C mit Hilfe verschiedener ESR-spektroskopischer Methoden für den R- und den Z-Gruppen-Ansatz unter Verwendung oberflächengebundener Trithiocarbonate als RAFT-Agenzien untersucht. Die kinetischen Analysen des R-Gruppen-Ansatzes mittels stationärer ESR-Experimente lieferten Gleichgewichtskonstanten Keq, die um eine Größenordnung kleiner sind als die Literaturwerte für entsprechende homogene Polymerisationssysteme, was darauf hindeutet, dass die Oberflächenverankerung des RAFT-Agens einen signifikanten Einfluss auf die Kinetik der RAFT-Polymerisation hat. Durch die Aufnahme zeitlicher Konzentrationsverläufe der Intermediatspezies und der propagierenden Radikale nach Einzelpulsinitiierung mittels der hochaufgelösten zeitabhängigen ESR-Spektroskopie (SP–PLP–ESR–RAFT) in Kombination mit PREDICI®-Simulationen wurden diese Ergebnisse bestätigt, da eine Abnahme des Geschwindigkeitskoeffizienten der Addition eines Makroradikals an die RAFT-Gruppe mit zunehmender Anzahl beteiligter oberflächengebundener Makromoleküle gefunden wurde. Dieser Befund ist im Einklang mit der Vorstellung, dass die Additionsreaktion bei Beteiligung verankerter Makromoleküle diffusionskontrolliert abläuft, was auf die unterdrückte Translations- und die eingeschränkte Segmentdiffusion oberflächengebundener Polymerketten zurückzuführen ist. Ein noch kleinerer Wert von Keq wurde für den Z-Gruppen-Ansatz gefunden und kann darauf zurückgeführt werden, dass die in Lösung wachsenden Ketten für die Additionsreaktion mit der RAFT-Gruppe, die sich über den gesamten Verlauf der Polymerisation in unmittelbarer Nähe zur Partikeloberfläche befindet, durch die Polymerschicht auf der Oberfläche diffundieren müssen. Die Wahrscheinlichkeit dafür, dass eine Additionsreaktion stattfindet, nimmt mit zunehmender Polymerschichtdicke ab, was durch einen kleineren Wert von Keq bei Verwendung von einem RAFT-Agens, das über die Z-Gruppe verankert war und über eine makromolekulare anstatt einer niedermolekularen R-Gruppe verfügte, gezeigt werden konnte. Die vorgestellten Ergebnisse geben einen umfangreichen Überblick über den Einfluss der Oberflächenverankerung von Komponenten, die am Prozess der radikalischen Polymerisation beteiligt sind, auf die Kinetik der oberflächeninitiierten radikalischen Polymerisation und ebnen den Weg für detaillierte, systematische Untersuchungen der Zusammenhänge zwischen der Kinetik von radikalischen Polymerisationen an Oberflächen und der molekularen Struktur der erhaltenen oberflächengebundenen Polymere.

Ce travail a consisté en la synthèse de nouveaux copolymères d’acétate de cellulose greffés par du poly(méthyl diéthylène glycol méthacrylate) avec un nombre et une longueur de greffons variables par une méthode de polymérisation radicalaire contrôlée : l’Atom Transfer Radical Polymerization (ATRP). Deux familles de matériaux ont été obtenues ayant mêmes compositions (entre 20 et 50% en masse de greffons) mais des architectures différentes : de nombreux greffons courts ou peu de greffons longs. Ces matériaux ont ensuite été étudiés pour la séparation par pervaporation de mélanges azéotropiques de type aprotique/protique : carbonate de diméthyle/méthanol et éthyl tert-butyl éther/éthanol. Pour la séparation du premier mélange, la réticulation des copolymères s’est avérée nécessaire, conduisant à des matériaux qui restent fragiles sous contrainte et qui présentent des flux élevés au détriment d’une très faible sélectivité. Pour cette séparation, ces matériaux permettent cependant de dépasser la limite thermodynamique imposée par l’azéotrope. Pour le mélange éthyl tert-butyl éther/éthanol, les copolymères montrent d’excellentes performances en extrayant l’éthanol de manière très sélective. L’introduction de greffons permet d’augmenter le flux de pervaporat tout en ne diminuant que faiblement la sélectivité par rapport à l’acétate de cellulose précurseur. L’analyse de la microstructure des copolymères montre que les copolymères avec peu de greffons longs sont beaucoup plus ségrégés que ceux avec de nombreux greffons courts. Les résultats de perméabilité montrent des comportements différents selon l’architecture du copolymère cohérents avec leur microstructure / This work deals with the synthesis of new copolymers of cellulose acetate grafted with poly(methyl diethylene glycol methacrylate) with different numbers and lengths of grafted chains by controlled radical polymerization (Atom Transfer Radical Polymerization ATRP). Two families of materials were obtained with the same compositions (between 20 and 50% in mass of grafted chains) but different architectures : a lot of short chains or a few long chains. These materials were then studied for the pervaporation separation of two aprotic/protic azeotropic mixtures : dimethyl carbonate/methanol and ethyl tert-butyl ether/ethanol. For the separation of the first mixture, copolymers had to be cross-linked but their mechanical withstanding was poor under stress and they showed high fluxes but very low selectivity. Nevertheless, the materials allowed to go over the thermodynamical azeotropic limit. For ethyl tert-butyl ether/ethanol separation, copolymers showed excellent performances with a very selective extraction of ethanol. The presence of grafted chains increased flux along with a slight decrease in selectivity compared with the cellulose acetate precursor. The analysis of the copolymer microstructure showed that copolymers with long grafted chains were more segregated than those with short grafted chains. The results of permeability showed different behaviours according to the copolymer architecture in good agreement with their microstructure

Cette thèse se concentre principalement sur l'activation du CO2 dans les polymérisations radicalaires et catalytiques des oléfines. Le polyéthylène a tout d'abord été synthétisé par un procédé de polymérisation radicalaire dans du CO2 supercritique (scCO2) dans des conditions douces (T? 100 °C, P? 300 bar) sans ajout de solvant organique pour solubiliser l'amorçeur. Nous avons utilisé l'AIBN, le peroxyde de lauryle ou le peroxyde de benzoyle pour étudier différents modes d'amorçage. La décarboxylation de ce dernier peut être supprimée dans le scCO2 et conduit à la formation de polyéthylène fonctionnalisé par des groupements esters. En outre, une interaction entre le triéthylaluminium (AlEt3) et les radicaux a été dévoilée, l'effet d'AlEt3 sur la polymérisation radicalaire de l'éthylène a été étudié, révélant son rôle d'agent de transfert de chaîne irréversible dans ce processus. Cette interaction, en combinaison avec celle d'AlEt3 avec le CO2 ont été exploitées pour permettre l'incorporation de CO2 dans les chaînes de polymère. Ainsi, si le motif CO2 est présent dans les chaînes de polyéthylène en utilisant AlEt3, le CO2 est bien pour la première fois un réactif efficace dans la polymérisation radicalaire de l'éthylène. D'autre part, des copolymérisations aléatoires et séquencées d'éthylène-isoprène par des procédés de transferts de chaînes à l'Aluminium catalysés par des complexes de fer ont été réalisées. Ensuite, chaque monomère a été polymérisé indépendamment dans du CO2 supercritique en utilisant le catalyseur de fer optimal lui correspondant afin d'obtenir des procédés plus écologiques pour la polymérisation de ces monomères dont le but ultime sera l'incorporation de motifs carboxyliques. Les essais visant à fonctionnaliser le polyéthylène et d'autres polyoléfines avec du CO2 à l'aide de diverses stratégies constituent un domaine d'intérêt majeur pour de futurs développements au sein de notre laboratoire / This thesis focuses primarily on the utilization of CO2 in radical and catalytic polymerizations of a-olefins. Polyethylene was synthesized by a free radical polymerization process in supercritical CO2 (scCO2) under mild conditions (T? 100 °C, P? 300 bar) without addition of any initiator diluent, using AIBN, lauroyl peroxide, or benzoyl peroxide to investigate different initiation modes. The decarboxylation of the latter can be suppressed in scCO2 to yield ester-functionalized polyethylene. Furthermore, an interaction between triethylaluminum (AlEt3) and radicals was unveiled, the effect of AlEt3 on ethylene radical polymerization was investigated showing its role as an irreversible chain-transfer agent in this process. This interaction in conjunction with the reactivity of AlEt3 towards CO2 were harnessed to allow for CO2-incorporation within polyethylene chains. Thus, since CO2 was incorporated within the polyethylene chains using AlEt3, CO2 for the first time behaved as an effective reagent in ethylene radical polymerization. On the other hand, ethylene-isoprene random and block copolymerizations via iron-catalyzed chain shuttling processes have been achieved. Subsequently, each monomer was polymerized in supercritical CO2 using its corresponding dedicated iron catalyst in order to achieve sustainable processes to polymerize these monomers with the hope of incorporating some carboxylic moieties. Trials to functionalize polyolefins by CO2 using various strategies is an area of interest in the upcoming work of our laboratory

A distribuição de pesos moleculares (DPM) de um polímero afeta as propriedades mecânicas, térmicas e reológicas do material. Além disso, a análise em tempo real de uma reação de polimerização é uma tarefa complicada e, consequentemente, os procedimentos de controle devem ser baseados em valores gerados pelos modelos. Por isso, é extremamente importante ter dados confiáveis sobre distribuições de pesos moleculares, melhorar a eficiência dos métodos existentes e desenvolver novos métodos capazes de prever as heterogeneidades das reações de polimerização. Experimentalmente, a DPM pode ser obtida usando técnicas como a cromatografia de permeação em gel. Para predizer a DPM, vários métodos foram desenvolvidos nas ultimas décadas. Um dos principais é o dos momentos estatísticos, baseado em conceitos puramente estatísticos, que não conseguem descrever completamente a DPM. Além disso, as aproximações com método de Galerkin usam polinômios ortogonais - no caso especifico polinômios de Laguerre - cujos coeficientes são calculados empregando os momentos estatísticos e a distribuição é gerada resolvendo um número de equações definido pelo usuário, relacionado à precisão desejada. Enfim, o método das funções geradoras de probabilidades foi utilizado para prever as DPMs, porém necessitando uma inversão da transformada de Laplace, que introduz problemas numéricos nem sempre possíveis de serem resolvidos. No presente trabalho, o sistema rigoroso de equações diferenciais ordinárias foi resolvido, com objetivo de reduzir as imprecisões e as limitações introduzidas pelas aproximações. Obter diretamente a DPM completa requer a resolução de um sistema contendo cerca de 2Nmax até 3Nmax equações diferenciais ordinárias rígidas, tarefa que há alguns anos era inviável devido a limitações relacionadas à capacidade de cálculo. Foi modelada a DPM para uma reação de polimerização radicalar livre de estireno e de metacrilato de metila. Um interesse especial foi dado à taxa de terminação que é, no momento, um dos temas mais investigados em polimerização por radicais livres. Os resultados das simulações foram comparados com dados experimentais tirados de reatores convencionais e, subsequentemente, com dados experimentais provenientes de um millireactor não convencional. / It is well known that the molecular weight distribution (MWD) of a synthetic polymer affects its mechanical, thermal and rheological properties. Furthermore, the on-line analysis for polymerization reaction is a difficult task and, consequently, the control procedures must rely on values given by models. As such, it is extremely important to have reliable data on the MWD, improve the efficiency of existing methods and develop new ones to predict the heterogeneities of polymerization reactions. Experimentally, the MWD can be obtained using techniques such as Gel Permeation Chromatography (GPC). To predict the MWD, many methods have been developed over the last decades. One of the main methods is the statistical moment treatment, which is based on a pure statistical concept and do not describe the whole MWD. Moreover, Galerkin approximation uses orthogonal polynomials -in general Laguerre polynomials- whose coefficients are calculated exploiting the statistical moment definition and the distribution is generated by solving a user-defined number of equations based on the desired precision. Finally, probability-generating functions that have been used to predict MWDs require Laplace transforms inversions, introducing numerical issues that must be bypassed and are not always solvable. It has been decided to base the approach without adopting any of these methods but directly solving the rigorous ordinary differential equation (ODE) system in order to reduce the inaccuracies and the limitations introduced by approximations. The direct obtention of the MWD requires the resolution of a system containing approximately 2Nmax up to 3Nmax stiff ODE equations that, a few years ago, was unfeasible due computational time limitations. The MWDs for a free radical styrene polymerization system and a methyl methacrylate system have been modeled. A special focus was given to the termination rate constant, which is, at the present, one of the most investigated topics in free radical polymerization. The results of the simulations were compared to experimental data taken from conventional reactors and, subsequently, to experimental data coming from an unconventional millireactor.

Materiais nanocompósitos híbridos polímero-argila nos quais lamelas nanométricas de argila montmorilonita são encapsuladas e dispersas em matriz polimérica são em geral mais rígidas, tenazes e resistentes do que os materiais poliméricos convencionais e tem o potencial de aplicações em revestimentos e filmes com propriedades de barreira. Dentre as várias técnicas de preparação de nanocompósitos poliméricos, as técnicas de polimerização \"in-situ\" em emulsão e mini-emulsão vem sendo empregada na síntese de látices híbridos com lamelas de argilas encapsuladas pelo polímero. Neste trabalho foram preparados látices híbridos de poliestireno e argila montmorilonita esfoliada através de dois métodos: no primeiro, a polimerização em emulsão e miniemulsão convencional na presença de argila modificada com sal quaternário de amônio é realizada com surfatante catiônico; no segundo método, um surfatante aniônico reativo foi usado para modificar uma argila natural sódica e empregada na polimerização em emulsão. Os resultados obtidos tanto para a polimerização em emulsão como em miniemulsão empregando idênticos reagentes (argila organofílica modificada e surfatante catiônico) mostraram boa conversão, aumento na velocidade de polimerização com aumento da concentração de surfatante e de argila, aumento na temperatura de pico na máxima velocidade de decomposição (TG), aumento no módulo de armazenamento no patamar vítreo e no patamar borrachoso (DMTA) com aumento da concentração de argila, encontrando um valor mínimo em ambos a 5% de argila. Apesar dessas características positivas, não foi obtida a encapsulação das lamelas da argila que era o objetivo principal do trabalho. Por outro lado, o método de polimerização em emulsão não convencional com surfatante reativo mostrou baixa eficiência na conversão mas que se mostrou eficaz na encapsulação das lamelas da argila para os látices com baixa conversão e elevado diâmetro de partícula. / Polymer-clay nanocomposite materials, in which nanometer-thick layers of clay dispersed in polymers, are generally stiffer, stronger, and tougher than normal polymeric materials and can be potentially useful in a variety of applications. These polymer-clay nanocomposites can be prepared in several ways, namely by emulsion \"in-situ\" polymerisation where polymer chains are coagulated on silicate layers producing capped silicate layers are more or less uniformly dispersed in aqueous medium. The objective of this work is to prepare polymer-clay hybrid latexes with exfoliated clay platelets encapsulated inside latex particles in order to improve the exfoliation of the clay platelets in the final polymeric film. To achieve this objective two separate approaches have been investigated, first by conventional emulsion polymerization and miniemulsion polymerization in the presence of montmorillonite clay modified by cationic surfactant and in the other approach a reactive anionic surfactant was used to modify the natural montmorillonite clay layers by emulsion polymerization. The results for both the emulsion polymerization as in miniemulsion using identical reagents (organoclay modified and cationic surfactant) showed good conversion, polymerization rate increased with increasing concentration of surfactant and clay, increased peak temperature at maximum speed decomposition (TG), an increase in storage modulus in the glassy plateau and the rubbery plateau (DMTA) with increasing concentration of clay, finding a minimum value in both the 5% clay. Despite these positive characteristics, encapsulation was not obtained from lamellar clay that was the main objective. Moreover, the method of emulsion polymerization with non-conventional reactive surfactant showed low conversion efficiency but has proved effective in the encapsulation of the lamellae of the clay for the lattices with low conversion and high particle diameter.

Les copolymères de PVDC possèdent des propriétés barrières à l'oxygène et à la vapeur d'eau qui en font un matériau de choix pour l'industrie de l'emballage alimentaire ou pharmaceutique. Les latex à base de PVDC (noté latex de PVDC) sont actuellement stabilisés par des tensioactifs de faibles masses molaires susceptibles de migrer dans le film après enduction et de dégrader ses propriétés. Le but de ce projet est donc la synthèse de latex de PVDC sans tensioactif en présence d'agents RAFT macromoléculaires (macroRAFT) hydrophiles qui jouent le rôle de stabilisants des particules tout en étant liés de manière covalente à celles-ci. La copolymérisation par RAFT du VDC a tout d'abord été étudié en milieu homogène. Des copolymères statistiques et des copolymères à blocs amphiphiles à base de VDC bien définis ont été synthétisés. Ensuite, des macroRAFT hydrophiles non ioniques et sensibles au pH, préformés en milieu organique, ont montré la possibilité d'obtenir des latex de PVDC où le bloc hydrophile stabilisant était lié de manière covalente aux particules. Enfin, un procédé intégralement dans l'eau a été mis au point avec des macroRAFT sensibles au pH ou chargés de manière permanente, synthétisés en milieu aqueux et utilisés directement dans la polymérisation en émulsion. Des latex stables de PVDC ont été obtenus à des taux de solide de 40 % à partir de faibles quantités de macroRAFT répondant ainsi aux exigences industrielles du projet. Les films formés à partir de ces latex auto-stabilisés sont transparents, ne blanchissent que très peu lors du contact avec l'eau, contrairement au film commercial de référence et ont montré des propriétés barrières supérieures / Since poly(vinylidene chloride) (PVDC)-based copolymers present unique oxygen and water vapor barrier properties, they are a material of choice for pharmaceutical blisters and food packaging. PVDC-based latexes used in coating applications are generally stabilized by low molecular weight surfactants, which are prone to migration in the film after coating and cause material degradation. The main goal of our project is the synthesis of surfactant-free PVDC-based latexes by using hydrophilic macromolecular RAFT agents (macroRAFT). The latter plays the role of precursor of stabilizer and limits migration phenomena by being covalently bound to particles. In a first part, RAFT polymerization of VDC was studied in homogenous solution. Well-defined statistical and amphiphilic blocks copolymers based on PVDC were synthesized. Then, PVDC-based latexes were obtained by emulsion polymerization mediated by hydrophilic non-ionic and pH sensitive macroRAFT pre-formed in organic solvent. Those hydrophilic segments were chemically anchored to the particles. A fully water-based process was developed by synthesizing in water pH sensitive and permanently charged hydrophilic macroRAFT which were further used directly in emulsion polymerization without additional purification. Stable PVDC-based latexes exhibiting solids content of 40 % were obtained using a very small quantity of macroRAFT, fulfilling the industrial requirements. Drying of self-stabilized latexes led to transparent films which display only a slight whitening after water exposition contrary to the commercial film reference and better barrier properties