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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Reversible addition-fragmentation transfer polymerization in heterogeneous aqueous media

McLeary, James Breton 04 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: The study presented in this dissertation had as primary aim to develop pathways to heterogeneous aqueous polymerizations that had living characteristics. To this end, the reversible addition fragmentation chain transfer (RAFT) process was investigated in predispersed and ab initio emulsions as well as homogeneous media. The synthesis of RAFT agents was carried out. The compounds prepared provided varied behaviour in reaction. In situ IH nuclear magnetic resonance (NMR) increased understanding of homogeneous RAFT mediated polymerizations. The early behaviour of RAFT mediated polymerizations led to the definition of initialization; a period before pre-equilibrium in a polymerization where degenerate behaviour occurs. Stable miniemulsion preparation methods were developed that provided living polymer latexes using high surfactant concentrations. The effect of surfactant concentration on particle size and latex stability was investigated. Living polymer characteristics were shown by the use of size exclusion chromatography, and 2- dimensional chromatography conclusively showed block polymer formation. In situ NMR spectroscopy of emulsions in deuterated water was used to provide evidence on the role of initiator solubility in polymerization. Secondary nucleation in high surfactant concentration miniemulsions systems was investigated using both particle size and molar mass analysis techniques and a means of eliminating secondary particle nulceation was shown through the use of aqueous phase radical traps. The role of the RAFT agent used in the polymerization was shown to be significant in determining the extent to which multiple polymer distributions formed in the polymerization in that radical exit from particles was affected. Finally, a new form of emulsion polymerization, which has been termed proto-seeded emulsion, has been developed. The proto-seed latex is formed by using a monomer whose polymer has chain length dependent water solubility. This process allows ab initio RAFT mediated emulsion polymerization to be conducted successfully without transport of RAFT agents in heterogeneous media. / AFRIKAANSE OPSOMMING: Die primerê doel in hierdie dissertasie is die ontwikkeling van roetes na heterogene water-gebaseerde polimerisasies met lewende eienskappe. Om hierdie doel te bereik is die omkeerbare addisie fragmentasie ketting oordrag proses (eng reversible addition fragmentation chain transfer (RAFT)) ondersoek in vooraf verspreide en direkte emulsies sowel as homogene media. Die sintese van RAFT agente is uitgevoer. Die verbindings wat voorberei is het verskillende einskappe in reaksies getoon. In situ IH kern magnetiese resonansie (KMR) het die kennis en begrip van homogene RAFT polimerisasies uitgebrei. Die vroeë gedrag van RAFT polimerisasies het tot die definisie van inisialisasie gelei; 'n periode voor die pre-ekwilibrium in 'n polimerisasie waartydens "degenerate" gedrag plaasvind. Stabiele miniemulsie voorbereidings metodes is ontwikkel wat lewende polimeer latekse verskaf het met gebruik van hoë seep konsentrasies. Die effek van seep konsentrasie op partikel grootte en lateks stabilitiet is ondersoek. Lewende polimeer eienskappe is bewys deur gebruik te maak van grootte-uitsluiting vloeistof chromatografie, en 2-dimensionele chromatografie het duidelik blok-polimeer vorming gewys. In situ KMR spektroskopie van emulsies in gedeutereerde water is gebruik om bewys te lewer van die rol van initieerder-oplosbaarheid in polimerisasie. Sekondêre nukleasie in hoë seep konsentrasie miniemuisie sisteme is ondersoek met die gebruik van beide partikel grootte sowel as molêre massa analise tegnieke. 'n Metode om sekondêre partikels te verhoed is verskaf deur gebruik te maak van waterfase radikaal lokvalle. Die rol van die RAFT agent in die polimeerisasie is beduidend in die graad van vorming van meer as een polimeer distribusie in die sin dat radikal uitgang van partikels beinvloed was. Ten slotte is 'n nuwe vorm van emulsie polimeerisasie ontwikkel wat proto-gesaaide emulsie genoem is. Die proto-gesaaide lateks is gevorm deur gebruik te maak van 'n monomeer waarvan die polimeer water-oplosbaarheid afhanklik is van die kettinglengte. Die proses laat ab initio RAFT emulsie polimerisasie toe om suksesvol uitgevoer te word sonder die vervoer van RAFT agente in heterogene media.
32

Nanosize latex particles via miniemulsion polymerization /

Anderson, Christopher D. January 2002 (has links)
Thesis (Ph. D.)--Lehigh University, 2002. / Includes bibliographical references and vita.
33

Stable Free Radical Polymerization Conducted In Emulsion Polymerization Systems

Maehata, Hideo 22 February 2010 (has links)
Free radical polymerization is the most common polymerization technique that is used for the manufacturing of polymers, due to the ease of the polymerization initiation, wide latitude of the material design for a large variety of monomers, and the excellent process robustness for commercial production. In the 1990’s, research activities for the precise control of radical polymerization process resulted in the discovery of ‘Living Radical Polymerization’. The discoveries opened the door for the next generation of radical polymerizations. Extensive research has been conducted to understand the mechanisms and kinetics for numerous practical applications, particularly for polymerization in bulk and solution systems. However, despite the interest of industry, the mechanistic understanding in aqueous dispersed systems such as emulsion and miniemulsion polymerization is far behind the aforementioned two systems. There are still major challenges from the production viewpoint. One reason for the poor understanding is the complexity of the heterogeneous system, which includes multiple reaction phases that are accompanied by the segregation and transfer of the reaction species among different phases. The purpose of this research was to investigate living radical polymerization or “Stable Free Radical Polymerization” (SFRP) in aqueous dispersed systems to obtain better mechanistic understanding of how the heterogeneous nature of the system interacts with the novel living radical chemistry. The theoretical and experimental feasibility of the SFRP emulsion process were studied in this research, in particular, focusing on the compartmentalization effect. Particle size influence on the polymerization kinetics and the polymer livingness was experimentally confirmed, and compared to bulk polymerization. In addition, a comprehensive mathematical model including all major chemical and physical events was developed to further our mechanistic understanding. Based on the results from the experimental and modeling studies, it was shown that rate reduction in the smaller particles is the primary cause of difficulty in implementing a conventional emulsion process (i.e. ab initio emulsion polymerization). Finally, for overcoming this difficulty, a new approach using a combination of TEMPO with highly hydrophobic 4-stearoyl TEMPO was proposed for a coagulum free ab initio emulsion process. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2010-02-18 09:49:52.336
34

Controlled Radical Polymerization in the Dispersed Phase

Thomson, Mary 07 December 2010 (has links)
Controlled radical polymerization (CRP) has emerged as a powerful method of creating polymers with tailored molecular architectures under mild reaction conditions. However, production of these polymers efficiently at an industrial scale will likely require them to be synthesized in the dispersed phase. Three types of CRP are explored, Atom Transfer Radical Polymerization (ATRP), Nitroxide Mediated Polymerization (NMP) and Catalytic Chain Transfer (CCT) to elucidate the intricacies of creating these novel polymer colloids. Compartmentalization in an ATRP dispersed phase system is explored theoretically to understand the effects of particle size and catalyst concentration on the polymerization. The results suggest that there is an optimal range of particle sizes where the rate of polymerization is greater than that in an equivalent bulk system while maintaining both a lower PDI (polydispersity index) and higher livingness. All three factors are desirable in ATRP but generally cannot be achieved simultaneously in bulk. Compartmentalization manifests itself differently in CCT dispersed phase systems, where the segregation of the CCT agents into different polymer particles leads to multimodal molecular weight distributions. Control over the particle size is notoriously difficult for nitroxide mediated polymerization, as it is challenging to decouple an increase in the particle size with an increase in target molecular weight using a two stage emulsion polymerization approach. This often leads to colloidally unstable latexes for low molecular weight, high solids conditions which are the result of superswelling. We offer several strategies to minimize this problem and create colloidally stable, high solids, n-butyl acrylate latexes by NMP with moderate to high molecular weight targets (>70 kg/mol). Using this synergy between target molecular weight and particle size, high solids (>40 wt.%), high molecular weight (<200 kg/mol) microemulsions (~20 nm) of methyl methacrylate-co-styrene were prepared. Finally, the monomer type and nucleation mechanisms also play a role in determining the particle size distribution in NMP emulsion systems. Using n-butyl methacrylate in emulsion with surfactant concentrations above the critical micelle concentration yields latexes with bimodal particle size distributions. However a surfactant-free approach allows monomodal latexes to be created. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2010-12-03 13:30:15.346
35

Aggregation and Redispersion of Switchable Latexes

O'NEILL, CATHERINE 26 September 2011 (has links)
Amidine-based switchable surfactants can be used as stabilizers during emulsion polymerization and the resulting latexes can then be destabilized by the removal of CO2. High Tg polymers have been successfully redispersed, as shown by recovery of primary particle size (measured by light scattering methods), but an input of energy was required. Sonication was the first method used, but lower-energy methods such as rotor-stators and a blender have also been successful in redispersing aggregated latexes. Colloidal stability was found to be reversible for at least three aggregation/redispersion cycles, and redispersibility was retained after the removal of water and addition of fresh water. Stimuli-responsive polymer colloids with reversible colloidal stability may have many uses. The shipping of latexes, for example, would be easier and less energy intensive if the latex particles could be aggregated and the bulk of the water removed. The latexes would then have to be redispersed prior to use. Switchable surfactants have also been used for the semi-continuous copolymerization of butyl acrylate and methyl methacrylate to form a high solids content (42 wt%), low-Tg latex. The latex can be destabilized with air and heat but cannot undergo redispersion because the low Tg polymer particles fuse upon aggregation. The copolymer, when dried at room temperature, formed a continuous film. Latexes with high solids content and low Tg’s are representative of latex paint formulations. Because the switchable surfactants have been shown to be successful in preparing these latexes, it is possible that they may be useful in the latex paint industry, for example as fast setting paints. / Thesis (Master, Chemistry) -- Queen's University, 2011-09-26 13:18:33.905
36

Kinetics of emulsion polymerization

Song, Zhiqiang 05 1900 (has links)
No description available.
37

Role of reactive surfactants in emulsion polymerization /

Lai, Zhen, January 2004 (has links)
Thesis (Ph. D.)--Lehigh University, 2005. / Includes vita. Includes bibliographical references.
38

Study of the incorporation of alkoxysilane monomers into model latex systems /

Marcu, Ioan, January 2003 (has links)
Thesis (Ph. D.)--Lehigh University, 2004. / Includes bibliographical references and vita.
39

Metal encapsulation of latex particles /

Kim, Hyungsoo, January 2006 (has links)
Thesis (Ph. D.)--Lehigh University, 2006. / Includes bibliographical references and vita.
40

Encapsulation of inorganic particles via miniemulsion polymerization /

Erdem, Bedri, January 1999 (has links)
Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 36-43, 88-90, 139-140, 187, 238-241, 282-285, 323).

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