Studies on Miniemulsion Polymerization and Their Applications in TEMPO-mediated Radical Polymerization
Date Issued
2009
Date
2009
Author(s)
Jeng, Jauder
Abstract
Miniemulsion polymerization and its applications in nitroxide-mediated living radical polymerization and in miniemulsion copolymerization were studied. In miniemulsion polymerization, both effects of costabilizer and mixed surfactants on the formation mechanism of droplets, miniemulsion stability, and growth mechanism of latex particles were detailed in chapters 2 and 3. Five results were obtained. 1. With increasing ultrasonication time, miniemulsions showed an initially broad droplet size distribution (DSD) and later reached a critically stabilized state in which monodispersed DSD was obtained. 2. The enhanced increase in cumulative volume (CV) fraction of smaller latex particles was resulted from droplet nucleation of shrinking droplets, owing to Ostwald ripening, and secondary nucleation. 3. Droplet nucleation dominated when HD conc. was high enough to effectively retard Ostwald ripening. 4. For higher n-hexadecyl trimethyl ammonium chloride (HTMA) concentration, droplet nucleation dominated because of denser surface coverage on particles. 5. For higher concentration of chitosan 100, secondary nucleation could not be ruled out because of lower effective surface coverage on particles. In applications of the miniemulsion polymerization in nitroxide-mediated living radical polymerization, it was detailed in chapter 4. 2,2,6,6-Tetramethylpiperidinyl-1-oxy (TEMPO) was used as a nitroxide. TEMPO-mediated living miniemulsion polymerization of styrene with feeding an ascorbic aqueous solution at a constant feeding rate throughout the polymerization was performed at 90oC under ambient pressure. Based on the author''s best knowledge, it was the first time that the TEMPO-mediated miniemulsion polymerization was performed under ambient pressure. Four results were achieved. 1. The higher the sodium dodecylbenzene sulfonate (SDBS) concentration, the denser the surface barrier on particles. Polymerization rate was thus slower. 2. The higher the concentration of ascorbic acid, the faster the TEMPO consumption. Polymerization rate was thus more rapid. 3. Living miniemulsion polymerization was primarily limited in surface zones of particles. 4. Livingness of polystyrene, resulted from the living miniemulsion polymerization, was identified by conducting bulk polymerization of chain extension. In the application of the miniemulsion copolymerization, the miniemulsion copolymerization, stabilized by SDS and HD, initiated by KPS, and conducted at 75 or 85oC in the presence of EHA, BA, or MMA comonomers, was evaluated in appendix A. Stable latex with low Tg of copolymer was produced. The latex exhibited higher conversion, low content of scrap, and well controlled composition in latex particles than those of conventional emulsion copolymerization. It was attributed to the unique mechanism of droplet nucleation in the miniemulsion copolymerization. Therefore, the miniemulsion copolymerization was a promising route in industrial production.
Subjects
miniemulsion
living miniemulsion polymerization
semi-batch process
ambient pressure
Type
thesis
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