No description available.

A series of five AB block copolymers of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) has been synthesised by the coupling of mono-functional homopolymers by an esterification reaction. In this series polymers all contain a PMMA component of number average molecular weight 908 gmo1·1, as measured by end group analysis, and the PEO components have number average molecular weights of 596, 689, 979, 2023 and 2884 gmol·1, as measured by proton nuclear magnetic resonance spectroscopy. Aqueous "solutions" of these copolymers have been prepared both by direct mixing and via methanol, a solvent for both blocks of the copolymer. Cloud points for these copolymers have been determined and range from 275K to 368K for the lowest and highest PEO blocks respectively. Small angle X-ray scattering (SAXS) of aqueous solutions has been interpreted in terms of a core - shell model and dimensions determined for both. Radii of gyration for the micellar cores have been shown to vary very little with variations in copolymer composition, concentration and temperature up to the cloud point. Fringe thicknesses show a dependence on PEO block length and relating measured fringe thicknesses to calculated chain conformations indicates that the the chain conformation is best described as an unperturbed chain. The measured fringe thickness is not altered by concentration or temperature up to the cloud point. Above the cloud point it is not possible to interpret the SAXS data in terms of a core shell micellar model. Significant differences in the SAXS data have been observed depending upon the mode of addition of copolymer to water. This can be interpreted as differences in micellar II structure With the exception of the lowest molecular weight copolymer all of the copolymers could be used as steric stabilisers for the aqueous emulsion polymerisation of methyl methacrylate. Polymerisations were only successful if the copolymer was introduced to the aqueous phase either via methanol or via the monomer. Direct addition of copolymer to water resulted in low polymerisation rates and unstable/flocculated products. Emulsions produced have been shown to be stable at pH levels where the electrophoretic mobility was zero, ie. the emulsions were sterically stabilised with no contribution from ionic I dipole interactions.

No description available.

No description available.

No / Core-shell particles have been prepared by surfactant-free emulsion polymerisations of butyl methacrylate in the presence of either linear or highly branched poly(acrylamidomethylpropane sulphonate)s (L-PAMPS or HB-PAMPS) with dithioate end groups: using a "shell-first" approach. In this method the water soluble PAMPS shells were anchored to the cores by polymerisation of BMA from the chain ends. The linear PAMPS produced non-crosslinked poly(AMPS-BMA) particles but the multiple chain ends of the highly branched PAMPS led to crosslinked particles. The particles were loaded with vascular endothelial growth factor or platelet derived growth factor, both of which are cytokines that are known to be important in the production of new blood vessels. The release of the growth factors was shown to be controlled by the architecture of the shell and we propose a mechanism that involves both ionic interaction of the PAMPS with the heparin-binding domains of the growth factors and size exclusion mediated diffusion.

Yes / A set of water-swollen core−shell particles was synthesized by emulsion polymerization of a 1,3-dioxolane functional monomer in water. After removal of the 1,3- dioxolane group, the particles’ shells were shown to swell in aqueous media. Upon hydrolysis, the particles increased in size from around 70 to 100−130 nm. A bicinchoninic acid assay and ζ-potential measurements were used to investigate the adsorption of lysozyme, albumin, or fibrinogen. Each of the core−shell particles adsorbed significantly less protein than the noncoated core (polystyrene) particles. Differences were observed as both the amount of difunctional, cross-linking monomer and the amount of shell monomer in the feed were changed. The core−shell particles were shown to be resistant to protein adsorption, and the degree to which the three proteins adsorbed was dependent on the formulation of the shell. / EPSRC and MRC

Fluorinated polymers are niche macromolecules that play an essential role in modern life. The special properties of fluorine, including among others, a large electronegativity (ca 3.98), low polarisability, small van der Waal’s radius (135 pm) and the strong C-F bond (ca 485 kJ · mol−1), impart unique properties to organofluorine compounds. Flu-oropolymers exhibit a combination of desirable traits, including high thermal stability, low coefficient of friction, chemical inertness, oleo- and hydrophobicity, and low surface tension. Among the fluoropolymers, polyvinylidene fluoride (PVDF), and copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), have found applications in the coatings industry as the binder in exterior coatings. The chemical inertness of poly(VDF-co-HFP) copolymer, however, prevents disper-sion of pigments into the coating and also inhibits adhesion of the coating onto substrates. An acrylic modifier polymer is typically added to the poly(VDF-co-HFP) copolymer to improve the dispersion of pigments and the adhesion of the coating. This acrylic copoly-mer is physically blended with the poly(VDF-co-HFP) copolymer on a macromolecular scale (i.e. it forms a thermodynamically miscible blend). The loading of acrylic copolymer in commercial PVDF coatings is often in the range of 20 to 30 % by weight of polymer solids. Typically, copolymers of methyl methacrylate, ethyl acrylate and methacrylic esters are employed. Alternative strategies to overcome the adhesion problem include, among others, chem-ical modification of the surface of the fluoropolymer film. This can be achieved by graft copolymerisation or core shell emulsion polymerisation. These methods are used to funcionalise the polymer chains, while maintaining the desirable properties of the parent polymer. Due to environmental regulations, industry focus has shifted towards develop-ing coatings with a low volatile organic compound (VOC) content. Aqueous, low VOC, air-drying coatings can be formulated directly from the acrylic modified fluoropolymer (AMF) latex and have superior properties to solvent based, high VOC, air-dry coatings. Their advantages include low viscosities, reduced flammability, reduced odour and easy application using conventional equipment. A large portion of the aqueous coatings are sold into the architectural market with over 70 % of architectural paints used in the United States being classified as aqueous. Arkema Inc. has developed a commercial aqueous fluoropolymer latex using the method of seeded emulsion polymerisation. VDF and HFP monomers are randomly copolymerised via emulsion polymerisation. This poly(VDF-co-HFP) copolymer may be used as the seed material in a core-shell polymerisation using acrylic monomers. Kato et al. [49] discloses the preparation of an AMF formulation for poly(VDF-co-HFP) copoly-mer. Preliminary testing of membrane textiles coated with such formulations showed that the AMF coatings degrade under UV irradiation more rapidly than is is expected for poly(VDF-co-HFP) copolymer. The patent indicates that the nature of the product formed by the emulsion polymerisation is not well understood and the product my be either a graft copolymer of a core-shell system. The aim of this research reported in this dissertation was to shed light on the nature of the final product, and to verify the claims made in the above-mentioned patent. Various acrylic monomers were copolymerised via seeded emulsion polymerisation us-ing commercial poly(VDF-co-HFP) copolymer as the seed material. The concentration and the ratios of the monomers were varied according to the formulation guidelines in Kato et al.[49]. ATR-FTIR spectroscopy and19F NMR spectroscopy was used to de-termine the microstructure of the resultant latexes. ATR-FTIR spectra confirmed the presence of C=C and C=O bonds in latexes. This indicates that unreacted acrylic com-ponents are present. The ATR-FTIR spectra of the films indicated the disappearance of the C=C bonds from the latex, which indicates that the monomers are evaporated easily from the latexes during film formation. The 19F NMR spectra confirmed that no modi-fication of the poly(VDF-co-HFP) copolymer backbone took place during the reactions. The particle size distribution graphs showed an increase particle sizes and this suggested that some self polymerisation of the monomer occurred. The viscosity of the latexes were lower compared to the due to the experiments being conducted under dilution. The flow characteristics of the poly(VDF-co-HFP) copolymer was also influenced with some reactions yielding shear thickening latexes as compared to the shear thinning poly(VDF-co-HFP) copolymerc. The reactions also yielded latexes which displayed lower and higher surface tensions than the poly(VDF-co-HFP) copolymer. Therefore, the conclusion may be drawn from this work that core-shell formation occurred during the emulsion copolymerisation, as opposed to grafting of the monomer onto the poly(VDF-co-HFP) copolymer backbone. The claims made in the literature could not be substantiated; in particluar, the reported improvements in film forming ability were not realised. No commercially useful advantage exists for the emulsion copolymerisation of poly(VDF-co-HFP) copolymer with acrylic monomers over the solution blending of poly(VDF-co-HFP) copolymer with acrylic copolymers. / Dissertation (MEng)--University of Pretoria, 2019. / Chemical Engineering / MEng / Unrestricted

Cette étude porte sur l’assemblage de particules à patchs pour obtenir de nouveaux matériaux. L’étatde l’art a permis de choisir et de mettre en oeuvre une stratégie originale dont la force motrice est l’assemblageinduit en milieu solvant, c’est-à-dire basé sur le caractère collant des macromolécules de polystyrène (PS)lorsqu’elles sont soumises à un mélange d’un bon et d’un mauvais solvant. Nous avons étudié l’assemblage enclusters, en chaînes ou en monocouches de nanoparticules (NPs) de silice possédant respectivement un, deux outrois patchs, constitués de macromolécules de PS greffées à des endroits spécifiques de leur surface. Les NPs desilice à un patch, présentant un rapport de taille patch/particule contrôlable, ont été synthétisées avec succès parune étape de séparation de phases induit par gonflement suivie d’un dépôt de silice régiosélectif. Leur assemblagea été réalisé dans des mélanges binaires DMF/éthanol. Les effets de la qualité du solvant, de la force decentrifugation, de la concentration en NPs, de la durée d'incubation et du rapport de taille patch/particule ont étéétudiés et discutés. La stratégie a été étendue pour obtenir des clusters à base d’or. Les NPs de silice à deuxpatchs ont été préparées par un procédé de polymérisation en émulsion ensemencée du styrène et le rapport detaille patch/particule a été ajusté via le taux de recroissance du noyau de silice. L’assemblage en chaînes des NPsa été réalisé dans des mélanges THF/solution aqueuse de NaCl en faisant varier la concentration en NaCl, lerapport volumique THF/eau, la durée d’incubation, la concentration en NPs et le rapport de tailles patch/particule.Nous avons montré que la cinétique de croissance des chaînes est typique d’une croissance par étapes. Desstratégies pour imiter des homopolymères, des copolymères statistiques, des copolymères séquencés à blocs etdes polymères ramifiés ont été mises en oeuvre, en utilisant comme briques de base des NPs à un patch, des NPsà deux patchs avec des tailles ou des fonctions de surface différentes et/ou des NPs à trois patchs. Les NPs desilice à trois patchs ont été obtenues par la même voie de synthèse que celles à deux patchs. Pour les assemblerdans des structures 2-D en nid d'abeille, nous avons utilisé la technique de Langmuir et nous avons étudiél'influence de différents paramètres expérimentaux. Une étape de recuit sous vapeur de THF a été mise en oeuvre,ce qui a permis de renforcer mécaniquement l’assemblage, mais sans effet significatif sur la compacité. / This study deals with the assembly of patchy particles to get new materials. The state-of-the-art allowedus to select and implement an original strategy whose driving force is the solvent-induced assembly, i.e. based onthe stickiness of polystyrene (PS) macromolecules when they are subjected to a mixture of good and bad solvents.We investigated the assembly into clusters, chains or monolayers of one-patch, two-patch or three-patch silicananoparticles (NPs), respectively, the patches being PS macromolecules grafted at specific positions on theirsurface. One-patch silica NPs with controllable patch-to-particle size ratio were successfully synthesised throughphase separation and site-specific silica coating. Their assembly was performed in DMF/ethanol binary mixtures.The effect of the solvent quality, centrifugation force, particle concentration, incubation time and patch-to-size ratiowas investigated and discussed. The strategy was spread to obtain gold-coated clusters. The two-patch silica NPswere prepared through a seed-growth emulsion polymerisation of styrene and the patch-to-particle size ratio wasadjusted through the extent of the silica core regrowth. The chaining of the NPs was efficiently achieved in theTHF/NaCl aqueous solution mixtures by varying the NaCl concentration, solvent quality, incubation time, NPsconcentration and patch-to-particle size ratio. We showed that the kinetics of the chaining process is characteristicof a reaction-controlled step-growth polymerisation. Strategies to mimic homopolymers, random copolymers, blockcopolymers and branched polymers were implemented by using one-patch NPs, two-patch NPs with different sizes/surface chemical functions and/or three-patch NPs as building units. The three-patch silica NPs were obtainedthrough the same synthetic pathway than two-patch ones. For assembling them in honeycomb-like 2-D structures,we used the Langmuir technique.and we studied the influence of different experimental parameters. THF vapourannealing was implemented to reinforce mechanically the assembly but without significative effect on the packingdensity.

Le sujet de cette thèse consiste à incorporer une couronne de polymère hydrophile à la surface de particules de latex par amorçage et croissance en utilisant la polymérisation radicalaire contrôlée par transfert d’atome induite par les métaux. Les particules de latex, obtenues par, polymérisation radicalaire en émulsion ont été fonctionnalisées avec un « inimère », monomère comportant une fonction halogénée capable de jouer le rôle d’amorceur dans l’étape de greffage. Cette étape de greffage a ensuite été effectuée en présence de CuBr2, PMDETA et d’un métal à valence zéro tel que le cuivre, àtempérature ambiante à partir de latex non post-purifiés (présence de tensio-actif et d’amorceur résiduels et à taux de solide élevés). Au cours du processus, l(incorporation de l’inimère et de la couronne hydrophile a été vérifée par ToF-SIMS (time-of-light secondary ion mass spectrometry), par FTIR et par l’étude des propriétés colloïdales des latex greffés. / The incorporation of a hydrophilic polymer shell at the surface of latex particles was studied using a “grafting from” approach based on aqueous metal-mediated radical polymerization. Latexes were synthesized via classical emulsion polymerization and functionalized at their surface by a comonomer bearing a Br-funcitonal group (the so-called inimer), which played the role of the initiator in the grafting reaction. Conditions under which the grafting could be performed at 25°C, using a real latex (no elimination of the surfactant anf the radical initiator), in the presence of CuBr2, N,N,N’,N’’,N’’-pentamethyldiethylenetriamine (PMDTA) and zero valent metal, in particulary Cu(0), were indentified. The success of the functionalization and grafting steps was evaluated by ToF-SIMS (time-of-light secoondary iom mass spectromtry), by FTIR and by the final properties of the so-formed core-shell particles.