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|Title:||Synthesis of multi-component polymer particles via seeded-emulsion polymerization||Authors:||Yam, Chun Ho||Degree:||Ph.D.||Issue Date:||2015||Abstract:||Development of novel strategies to prepare multi-component polymeric (MCP) particles is scientifically and technologically important because the MCP particles can possess multi-functionalities, intriguing hierarchical nanostrustures and synergistic properties of different components. Current synthetic approaches to prepare this kind of particles often suffer from some major drawbacks such as time-consuming solvent treatment, addition of large amount of stabilizers and emulsifiers, complicated multi-stage polymerization, and formation of relatively large particles. Thus, this thesis aims to develop a versatile and robust synthetic approach to synthesize multi-component amphiphilic core-shell particles in one-pot polymerization. The new approach is based on semi-batch seeded emulsion polymerization, which could be scale up for mass production. Various types of multi-component polymer nanoparticles were synthesized from different kinds of seed particles, including hard, soft and temperature-sensitive materials. The shell of the particles could be altered from a pH-responsive only to both pH- and temperature-responsive materials. The novel approach developed in this research allows us to fabricate multi-component polymeric particles with different nanostructures and compositions. It opens up an amenable pathway to commercial production of multi-component polymeric particles. The thesis begins with the definition of multi-component polymer (MCP) particles. Possible morphologies of the MCP particles and key principles for the formation of these special morphologies are discussed in detail. Current approaches to prepare MCP particles and their limitations are presented. Lastly, the core-shell particle platform technology developed by Li’s group and their potential applications are illustrated. Chapter Two introduces the motivation of this project. Specific objectives of this research to develop three-component amphiphilic core-shell particles are highlighted. Chapter Three describes the synthesis of MCP particles using PMMA/PEI as the seed particles. The seed particles were initially formed through a graft copolymerization of methyl methacrylate (MMA) from polyethyleneimine (PEI) via a redox initiation. Second hydrophobic monomer, such as styrene or n-butyl acrylate (n-BA), was subsequently added and polymerized within the seed nanoparticles to form MCP particles. Two types of PMMA/PEI based MCP particles, namely poly(n-butyl acrylate)/poly(methyl methacrylate) /polyethyleneimine (PBA/PMMA/PEI) and polystyrene/poly(methyl methacrylate) /polyethyleneimine (PS/PMMA/PEI), were synthesized and systematically characterized by different analytical methods. Under optimum reaction pH, the PBA/PMMA/PEI MCP particles possessed amphoteric property arising from the presence of positively charged amino groups and negatively charged carboxylic acid groups that were formed via the hydrolysis of the ester group. These amphoteric MCP particles were colloidally stable over the whole pH range.
Chapter Four discusses the synthesis of MCP particles using N,N’-methylene bis(acrylamide)-crosslinked poly(N-isopropyl acrylamide) /polyethyleneimine (PNIPAm-MBA)/PEI as seed particles. The (PNIPAm-MBA)/PEI seed nanogel was first formed by a graft copolymerization of N-isopropyl acrylamide (NIPAm) from PEI via a redox initiation. MBA was utilized as a crosslinker for the PNIPAm/PEI seeds. Second hydrophobic monomer, such as MMA, styrene or n-BA, was subsequently added and polymerized in the presence of seeded nanoparticles to form MCP particles. Three types of smart MCP particles, namely PMMA/(PNIPAm-MBA)/PEI, PBA/(PNIPAm-MBA)/PEI and PS/(PNIPAm-MBA)/PEI, were successfully synthesized. All of these smart MCP particles exhibited pH- and temperature-responsive properties. Degree of MBA crosslinking was found to affect the pH- and temperature-responsive properties of the MCP particles. The particle morphology and nanostructure were revealed by Field-Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM). The inner core of MCP particle was constructed with hydrophobic polymer of PMMA, PBA or PS, while the outer shell of MCP particle was an interpenetrated network, comprising of pH-responsive PEI and temperature-responsive PNIPAm. Interestingly, MCP particles with different morphologies were obtained when using different monomers as the second batch of hydrophobic monomers. The PS/ (PNIPAm-MBA)/PEI and PBA/(PNIPAm-MBA)/PEI MCP particles displayed spherical morphology, while PMMA/(PNIPAm-MBA)/PEI MCP particles possessed aerolite-like morphology with many PMMA micro-domains evenly distributed in the particles matrix. Chapter Five describes further investigation of MCP particles using non-crosslinked PNIPAm/PEI as seed particles based on the previous findings described in chapter Four. PNIPAm/PEI micelle-like seed nanoparticles were first formed by the graft copolymerization of NIPAm from PEI via a redox initiation. Second hydrophobic monomer, MMA or styrene, was subsequently added and underwent seed emulsion polymerization, giving stable MCP particles. Two types of MCP particles, PS/PNIPAm/PEI and PMMA/PNIPAm/PEI, were successfully prepared. The temperature-responsive properties of MCP particles could be adjusted by varying the weight ratio between seed monomer and second batch monomer. MCP particles with different morphologies were produced when using various second batch hydrophobic monomers. Spherical particles were obtained when styrene was used as the second batch monomer, while the use of MMA gave aerolite-like particles. The properties of the resulting particles, including particle size and size distribution, surface charge, chemical composition and morphology, have been systematically characterized by dynamic light scattering, ζ-potential measurement, Fourier-transform infra-red spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. The pH-responsive property of the shell of the particles was confirmed by ζ-potential measurement at different pHs. Chapter Six concludes the essential findings obtained in this thesis. The synthesis and smart responsive properties of MCP particles were also summarized. Mechanism of MCP particle formation leading to various nanostructures was proposed. The final Chapter provides recommendations for further development of MCP particles. Future works include fabrication of different functional MCP particles and exploration of MCP particles as protective coating.
Hong Kong Polytechnic University -- Dissertations
|Pages:||xix , 372 pages : illustrations (some color)|
|Appears in Collections:||Thesis|
View full-text via https://theses.lib.polyu.edu.hk/handle/200/8037
Citations as of May 22, 2022
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