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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.

Orientador: Fernando Galembeck / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-20T05:17:46Z (GMT). No. of bitstreams: 1 Shah_Ziarat_D.pdf: 4969142 bytes, checksum: 3a691c84e8047244b2a5b14d8573efa1 (MD5) Previous issue date: 2012 / Resumo: Neste trabalho foram sintetizados latexes do poli[estireno-co-(acrilato de butila)-co-(acido acrilico)], com a mesma composicao monomérica, sob as mesmas condições experimentais, mas utilizando diferentes tensoativos. Foram utilizados tensoativos não-iônicos, derivados etoxilados (EO) do nonilfenol (NP), álcool laurílico e do álcool oleico, apresentando numeros de grupos EO por molecula igual a: 4 e 100, 23 e 20, respectivamente. Foi também empregado o tensoativo aniônico, dodecilsulfato de sódio (SDS). Os polímeros foram sintetizados através do método da pré-emulsão, a 75ºC, sob atmosfera de nitrogênio e usando persulfato de sódio, como iniciador. Os latexes obtidos foram caracterizados através das seguintes técnicas: espectroscopia vibracional na região do infravermelho (FTIR), espectroscopia por correlação de fótons (PCS), calorimetria de varredura diferencial (DSC), analise termogravimétrica (TGA), centrifugação zonal em gradiente de densidade, ensaio de adesão, microscopia de força atômica (AFM), microscopia eletrônica de varredura (SEM) e microscopia eletrônica de transmissão (TEM). Os espectros FTIR são similares, mas apresentam diferenças nítidas em algumas regiões espectrais. Os resultados obtidos das análises térmicas indicam que uma maior quantidade de água não congelável ligada está presente no latex sintetizado a partir da mistura de tensoativos não iônico NP(EO)40 e aniônico SDS, sendo que a fração de massa de água livre é quase igual em todos os latexes. Os resultados de TGA mostram que a degradação dos latexes ocorre em etapas diferentes, sendo que a diferença na faixa de temperatura de decomposição dos diferentes latexes não é muito significativa, exceto no caso da amostra sintetizada usando a mistura de NP(EO)40 e SDS. Os resultados dos estudos microscópicos mostram uma grande variabilidade nas particulas formadas, na rugosidade e nos padrões de distribuição da viscoelasticidade nas superfícies dos filmes. Esta tese demonstra que é possivel obter latexes muito diferentes com os mesmos monômeros e mesmo procedimento de polimerização, mas mudando simplesmente o tensoativo / Abstract: In this work six different latexes of poly[styrene-co-(butyl acrylate)-co-(acrylic acid)], were synthesized under similar experimental conditions and monomer composition by changing the surfactants only. The surfactants used were ethoxylated nonylphenol NP(EO)n, lauryl alcohol and oleic alcohol, with (EO) chain lengths equal to 4, 100, 23 and 20, respectively. The anionic surfactant sodium dodecyl sulfate (SDS) was also used. The polymers were synthesized by the semi-batch emulsion polymerization method at 7ºC under nitrogen atmosphere using sodium persulfate, as a free-radical initiator. The latexes were characterized using Fourier transform infrared spectroscopy (FTIR), photon correlation spectroscopy (PCS), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), zonal density gradient centrifugation, film adhesion, atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The FTIR spectra are similar but also show differences in some spectral regions. The DSC results present that a significant fraction of non-freezing bound water was found in the latex stabilized with a mixture of NP(EO)40 with (SDS), and the percentage of free water was almost equal in all samples. TGA results show that the complete thermal degradation of latexes occurs at different temperature and difference in the decomposition temperature was not very significant, except for the sample synthesized with a mixture of SDS and NP(EO)40 surfactants. The results of microscopy studies show a great variability in the particles formed, surface roughness and in the distribution pattern of viscoelasticity on the film surfaces. This thesis demonstrates that that it is possible to obtain very different latices with the same monomers and the same polymerization procedure but simply changing the surfactant / Doutorado / Físico-Química / Doutor em Ciências

Cellulose nanocrystals (CNCs) are attractive nanomaterials due to their superior mechanical properties, renewability, and natural abundance. Their surface hydroxyl groups, along with surface charges induced during their production, allow CNCs to be easily dispersed in an aqueous medium, especially with sustainable water-based production methods such as emulsion polymerization. Moreover, their surface functionality makes them highly suitable for modification, thereby making them even more versatile. Emulsion polymer latexes are heterogeneous mixtures, having a continuous aqueous phase along with a dispersed organic phase. Latex polymers are used in a wide range of applications such as in coating and adhesive films. Because of the bi-phasic nature of emulsion polymerizations, the surface properties of CNCs play a crucial role in their location relative to the organic phase, and how well-dispersed they are in the cast films. In this thesis, three grades of CNCs (Celluforce Inc.) with either hydrophilic, partially-hydrophobic, or hydrophobic surface properties, were combined with conventional emulsion and miniemulsion polymer formulations to investigate their effect on the properties of pressure sensitive adhesive (PSA) films. In the first instance, hydrophilic CNCs were tested in a seeded semi-batch emulsion polymerization. Using a sequential experimental design, the effects of polar comonomer, surfactant, chain transfer agent, and CNC loading on latex stability and PSA properties were studied. By increasing polymer chain entanglements and the work of adhesion, the hydrophilic CNCs were observed to simultaneously improve the three key properties of acrylic-based PSA films, i.e., tack, peel strength and shear strength. In the second part of this project, we compared the role of hydrophilic and partially-hydrophobic CNCs in PSA property modification. Viscosity measurements and atomic force microscopy revealed differences in the degree of association between the two types of CNCs and the latex particles. Dynamic strain-sweep tests showed that hydrophilic CNC nanocomposites softened at lower strains than their partially-hydrophobic counterparts. This behaviour was confirmed via dynamic frequency tests and modelling of the nanocomposites’ storage moduli, which suggested the formation of CNC aggregates of, on average, 3.8 and 1.3 times the length of CNCs. These results confirmed that the partially-hydrophobic CNCs led to improved CNC dispersion in the PSA films and ultimately, enhanced PSA properties. In the third part of the project, mini-emulsion polymerization (MEP) was used to embed the hydrophobic CNCs within the polymer particles in contrast to the hydrophilic and partially-hydrophobic CNCs which resided mainly in the aqueous phase or near the water-particle interface. Higher CNC loadings led to increased particle size, decreased polymerization rate and number of particles, while only slightly increased the viscosity and the work of adhesion. PSA film properties decreased upon the incorporation of hydrophobic CNCs. Transmission electron microscopy showed that CNCs were expelled from the latex particles at higher loadings, suggesting the incompatibility of the acrylic polymer and the CNCs’ modifying agents. The ability to modify CNCs enables one to achieve a range of hydrophilicity/hydrophobicity. This makes them extremely versatile in a heterogeneous mixture such as in an emulsion polymerization. Because emulsion polymers are used in a wide range of applications with a broad spectrum of properties (i.e., not only as adhesives but as non-tacky coatings), our ability to control CNC location relative to the polymer particles in the latex opens the door to a world of high value-added sustainable polymer products.

No description available.

In this thesis, copolymer latexes comprised of various fractions of methyl methacrylate (MMA) and butyl acrylate (BA) were synthesized through surfactant-free emulsion polymerization. A carbon dioxide responsive comonomer, 2-(diethyl)aminoethyl methacrylate (DEAEMA) was also used with an equimolar amount of hydrochloric acid (HCl) to promote its partitioning into the water phase. Changing the MMA/BA fraction gave control over the resulting glass transition temperature of the particles. Following polymerization, the particles from the resulting latexes could be effectively coagulated be adding a small amount of caustic soda, and could be easily separated from water. After washing the particles with deionized water, CO2-redispersibility of the latex particles was evaluated as a function of their respective glass transition temperature. It was determined that coagulated particles higher in MMA content could be easily redispersed into carbonated water with the aid of ultrasonication, preparing stable latexes of the same solids content. For latex particles with a glass transition temperature below ambient conditions, coagulation led to the fusion of individual particles, which inhibited their ability to be redispersed. By conducting the coagulation and redispersion cycles at temperatures cold enough for the BA-rich particles to be below their glass transition temperature, these same latex particles could be effectively redispersed. The relationship between the glass transition temperature of the latexes and their CO2-redispersibility provides guidance from a practical sense for the applicability of CO2-sensitive amine-functionalized molecules in developing industrially useful CO2-redispersible latex products. / Thesis / Master of Applied Science (MASc) / This work examines special type of coagulatable and redispersible latex paint that could potentially reduce the costs in storing and transporting latex paint products. After synthesizing the latex, the nanoscopic polymer particles that make up the latex could be easily coagulated by adding a small amount of sodium hydroxide. Following this, water could be removed and a condensed form of the paint was obtained. The ability to redisperse the particles back into carbonated water was subsequently examined based on the softness of the polymer particles by synthesizing a series of latexes with different fractions of methyl methacrylate (MMA) and butyl acrylate (BA). After synthesis, the latexes that contained higher fractions of MMA were comprised of particles that were less soft than the BA-rich latexes, which made the redispersibility of these particles much easier. Upon coagulation, BA-rich particles fused together upon contact and could not be separated, hence inhibiting their redispersibility. When these same BA-rich latex particles were coagulated at colder temperatures, fusion was inhibited and the redispersibility of particles was greatly improved. Overall, the particles were found to be redispersible if the glass transition temperature of polymer chains within the particles was lower than ambient temperature. Since softer polymer particles are often used for latex paint-based applications, this work provides important and relevant insight in the development of industrially useful CO2-redispersible products.

Synthèse et étude de nouveaux NHC-Boranes pour leurs propriétés énergétiques et leurs rôles en tant que photo co-amorceurs pour la photopolymérisation en émulsion.Depuis la première synthèse de complexes N-Hétérocycliques Boranes (NHC-Borane) stables en 1993, une étude plus générale de propriétés et réactivité n’a débuté que dans le milieu des années 2000. Les domaines d’applications de ces composés qui sont des paires de Lewis vont de la synthèse organique (agent réducteur, hydroboration de liaisons multiples) en passant par la chimie radicalaire (remplacement de l’hydrure de tributylétain, hydroboration) ou même en tant qu’amorceur ou co-amorceur de polymérisations.L’objet de cette thèse était d’étendre l’application des NHC-Boranes dans deux domaines précis. Un premier axe porte sur les propriétés hypergoliques amenées par leurs structures inédites. Un second est consacré à l’amorçage de réactions de polymérisations en émulsion et l’obtention de particules hybrides sous irradiation visible.Nous avons choisi et synthétisé de nouvelles cibles polyazotées qui ont montré des propriétés énergétiques potentiellement intéressantes pour l’usage de NHC-Boranes en propulsion solide. L’étude mis en évidence des différentes de réactivités en fonction du squelette du carbène utilisé. De plus, un nouveau type de carbène borane pouvant être utilisé dans différents domaines a été synthétisé.Nous avons aussi amélioré la compréhension du système de photoamorçage déjà proposé en polymérisation en émulsion dans le visible. Des points clés, sur la conception du système et du réacteur ont été améliorés. Nous avons aussi pu remplacer le tensioactif utilisé pour proposer la première photopolymérisation en émulsion Pickering. Il en résulte des latex stables, composés de particules hybrides pouvant former des films potentiellement anti-UV. L’excitation dans le visible, pourrait être utilisée dans le but de réduire les coûts énergétiques et même former d’autres particules inédites en évitant la dégradation de composés thermo ou UV-sensibles / Study and synthesis of new NHC-Boranes usable as hypergolic fuels and as photo co-initiators for radical emulsion photopolymerizationsThe first N-Heterocyclic Carbene Borane complex (NHC-Borane) was synthetized in 1993, but we had to wait until the mid-2000s before chemists investigated their properties and reactivity. The applications of NHC-Boranes range from organic chemistry (where they are used as reducing agents or for the hydroboration of multiple bonds) to radical chemistry (as replacement of te tributyltin hydride) and radical polymerizations (initiators and co-initiators). We designed and synthetized new Nitrogen-rich NHC-Boranes. The latter are hypergolic and might serve as fuels for solid propulsion. We managed to synthetize several new classed of NHC-Borane which was or could be used in different fields. We also deepened our understanding of the visible light-induced emulsion polymerization, where the NHC-Boranes serve as co-initiators. We could optimize the process and then replaced the surfactant by an inorganic sol to propose the first Pickering emulsion photopolymerization. Stable latexes of hybrid particles have been generated which might be used as sunscreen films, to reduce the energetic footprint of the reactions and/or to access particles made of heat- or UV-sensitive materials

Neste trabalho estudou-se o processo de coplimerização em emulsão de estireno e acrilato de butila em processo semicontínuo onde o produto final é um látice com alto teor de sólidos. Foi realizada uma série de experimentos de copolimerização em emulsão em um reator de vidro, empregando receitas com teores de sólidos na faixa de 50 a 64% em massa. Foram estudados os seguintes fatores: teor de sólidos, teor de ácido acrílico, teor de emulsificantes e tempo de adição dos monômeros. Os efeitos estudados são avaliados principalmente em termos de conversão, diâmetro médio das partículas, concentração de partículas, número médio de radicais por partícula, taxa de polimerização, viscosidade e fração de coágulos. Também se avaliou a distribuição de tamanhos de partículas para o processo. Utilizando informações experimentais e da literatura, foi aplicado um modelo matemático para o processo, com razoável adequação aos dados experimentais. / The aim of this work was the study of the high solid contents emulsion copolymerization of styrene and butyl acrylate in semi-batch process. Copolymerization reactions were undertaken in a glass reactor, and recipes with solid contents up to 64 wt.% were used. Were evaluated the effects of: solid contents on recipe, amounts of acrylic acid and surfactants on recipe and monomer feeding time. The effects were evaluated in terms of conversion, particle mean diameter, and particle concentration, average number of radicals per particle, polymerization rate, viscosity and coagulum content. It was performed a characterization of the particle size distribution for this process. Using experimental observations and literature information, it was applied a mathematical model for this process, with satisfactory agreement with experimental data.

Este trabalho descreve a síntese de látices poliméricos híbridos contendo a argila natural Montmorilonita (MMT) por meio da polimerização radicalar controlada via mecanismo de transferência reversível de cadeia por adição-fragmentação (RAFT) em emulsão sem adição de surfatante. Primeiramente, copolímeros anfifílicos com diferentes estruturas e composições, foram preparados por meio da polimerização via RAFT em solução e caracterizados por ressonância magnética nuclear de hidrogênio (RMN 1H) e cromatografia por exclusão de tamanho (SEC). A interação entre os copolímeros sintetizados, chamados de macroagentes RAFT, e a superfície da MMT foi estudada por meio de isotermas de adsorção experimentais, as quais foram ajustadas por modelos teóricos. Os macroagentes RAFT à base de ácido acrílico (AA), acrilato de metil éter poli(etileno glicol) (PEGA) e acrilato de n-butila (BA) apresentaram afinidade pela argila como mostraram as isotermas do \"tipo L\" (Langmuir) obtidas. Os látices híbridos preparados utilizando esses macroagentes RAFT foram analisados por microscopia eletrônica de transmissão em temperatura criogênica (cryo-TEM), que revelou lamelas de MMT decoradas com nanopartículas poliméricas. As isotermas de adsorção dos macroagentes RAFT catiônicos à base de metacrilato de 2-(dimetilamino)etila (DMAEMA), PEGA e BA foram do \"tipo H\" (alta afinidade). Esses macroagentes RAFT possibilitaram a preparação de dispersões estáveis de complexos de MMT/macroagente RAFT, o que foi verificado por espalhamento dinâmico de luz (DLS), e sua utilização na síntese de látices híbridos levou à formação de uma camada polimérica em torno das lamelas de MMT. Os filmes poliméricos nanocompósitos obtidos a partir de látices catiônicos estáveis de poli(metacrilato de metila-co-acrilato de n-butila)/MMT apresentaram melhor estabilidade térmica e melhores propriedades mecânicas do que os filmes poliméricos preparados sem adição de argila como mostraram, respectivamente, os resultados de análise termogravimétrica (TG) e de análise termodinâmico-mecânica (DMA) dos materiais. / This work describes the synthesis of hybrid polymer latexes containing natural Montmorillonite clay (MMT) by reversible addition-fragmentation chain transfer (RAFT)-mediated surfactant-free emulsion polymerization. Firstly, amphiphilic copolymers with different structures and compositions were prepared by RAFT polymerization in solution and characterized by hydrogen nuclear magnetic resonance (1H NMR) and size exclusion chromatography (SEC). The interaction between these copolymers (referred to as macroRAFT agents) and the MMT surface was studied by experimental adsorption isotherms, which were adjusted by theoretical adsorption models. MacroRAFT agents based on acrylic acid (AA), poly(ethylene glycol) methyl ether acrylate (PEGA) and n-butyl acrylate (BA) displayed affinity for MMT as shown by the \"L-type\" (Langmuir) isotherms obtained. The hybrid latexes prepared using these macroRAFT agents were analyzed by transmission electron microscopy at cryogenic temperatures (cryo-TEM), which revealed polymer-decorated MMT platelets. The adsorption isotherms of cationic macroRAFT agents based on 2-(dimethylamino)ethyl methacrylate (DMAEMA), PEGA and BA were of the \"H-type\" (high affinity). These RAFT macroRAFT agents allowed the preparation of stable dispersions of MMT/macroRAFT agents complexes, which was verified by dynamic light scattering analysis (DLS), and their use in the synthesis of hybrid latexes led to the formation of a polymer layer surrounding the MMT platelets. Nanocomposite films obtained from stable cationic latexes of poly(methyl methacrylate-co-n-butyl acrylate)/MMT showed better thermal stability and better mechanical properties than polymer films prepared without addition of clay as shown, respectively, by the results of thermogravimetric analysis (TG) and dynamic mechanical analysis (DMA) of the final materials.