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The role of solid particles in emulsion polymerization – synthesis and kinetic studies
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Lotierzo, Andrea (2019) The role of solid particles in emulsion polymerization – synthesis and kinetic studies. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3451836~S15
Abstract
Control of particle morphology and chemical functionality in polymer dispersions have been of growing interest in the scientific community for the past decades. The possibility of regulating asymmetry, in both shape and chemical composition, has been sought as a way of creating complex advanced materials. In these materials the mechanical and physico-chemical properties of different phases are combined, in a synergistic way, in an attempt of mimicking nature’s behaviour.
This thesis particularly deals with nanocomposite materials: materials where at least one of the different phases has two or three dimensions of less than 100 nanometres. Among the plethora of synthetic pathways developed for the controlled synthesis of nanocomposite colloids, this work focuses on a process called Pickering emulsion polymerization; a seeded emulsion polymerization reaction where a polymer phase is formed in-situ in the presence of a stabilizing nano-sized colloid formed ex-situ. The product of the reaction typically is that of a polymeric particle surrounded by a dense shell of stabilizing agent. The main advantages are the ease of operation, absence of high shear homogenization steps and of molecular surfactants. The latter is of key importance for instance in coating applications where surfactant migration during and after film formation can be detrimental for the final film properties.
In this work, initially Pickering emulsion polymerization is thoroughly explored from a kinetic and mechanistic viewpoint using a model system consisting of SiO2 nanoparticles and styrene or methyl methacrylate as monomers. These relatively well-known systems are used to draw more conclusive theories on the mechanism governing particle formation and specifically the mode of stabilizer adsorption at the polymer interface. Once assessed the main processes influencing the fate of the reaction, a first step towards the implementation of added complexity in the system is taken by moving towards polymeric block copolymer stabilizers, where the chemical composition can be tailored by changing the type of monomer used. Both dispersion and emulsion polymerization approaches are discussed, with a particular focus on the development of protocols which do not contain added coloration or malodorous compounds. This increases the complexity of the system as the adopted chain-transfer agents require to operate in monomer starve fed conditions in order to allow control over chain-growth. This was found not to be compatible with dispersion polymerization, or polymerization induced selfassembly, reaction conditions. Nevertheless, a solution to the problem is proposed which yielded polymer self-assemblies of various morphologies.
Finally, nanometric polymeric stabilizers (i.e. crosslinked block copolymer micelles, or nanogels) produced by the more successful emulsion polymerization approaches are adopted in Pickering emulsion polymerization reactions as sole stabilizers. The controlled destabilization of the nanogels by pH adjustment and background electrolyte addition led to polymer colloids of Janus, patchy or armoured morphology. Such particles are characterized by a given number of surface protrusions, with the same chemical composition as the nanogels adopted in the protocol.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QD Chemistry | ||||
Library of Congress Subject Headings (LCSH): | Emulsion polymerization, Polymer colloids, Nanogels | ||||
Official Date: | May 2019 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Chemistry | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Bon, Stefan Antonius Franciscus | ||||
Format of File: | |||||
Extent: | xxiii, 181 leaves : charts, illustrations | ||||
Language: | eng |
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