迷你乳化聚合反應及其在活性自由基聚合反應之應用的研究

Abstract

本研究深入探討迷你乳化聚合反應及其在活性自由基聚合反應與迷你乳化共聚合反應的應用。在迷你乳化聚合反應方面，研究內容記錄在第二與第三章，是深入研究共同安定劑與混合界面穩定劑對油滴形成機制、迷你乳液安定性與乳液顆粒成長機制等重要特性的效應，獲得以下五點結論：1) 隨著超音波震盪時間增加，油滴最初由很寬的粒徑分佈，逐漸達到穩定狀態，並且粒徑分佈轉變為較窄且單一的分佈；2) 較小的乳液顆粒來自於縮小油滴的油滴成核反應與二次成核反應；3) HD濃度高到足以有效延遲Ostwald ripening時，油滴成核反應佔優勢；4) HTMA濃度較高時，油滴成核反應佔優勢，因為界面穩定劑在顆粒表面的覆蓋率較高；5) Chitosan 100濃度較高時，二次成核反應無法忽略，因為界面穩定劑在顆粒表面的有效覆蓋率較低。在迷你乳化聚合反應的應用方面，研究內容記錄在第四章，是以TEMPO為媒介之苯乙烯的活性自由基迷你乳化聚合反應，反應條件是在90oC與環境壓力下，同時以半批次方式連續加入ascorbic水溶液。根據我們的調查，這是首次在環境壓力下，以TEMPO為媒介，進行活性迷你乳化聚合反應的研究，獲得以下四點結論：1) SDBS濃度愈高，顆粒表面的surface barrier愈密緻，因此反應速率愈慢；2) Ascorbic acid濃度愈高，TEMPO被消耗地愈快，因此反應速率愈快；3) 活性迷你乳化聚合反應主要是在顆粒的surface zone進行；4) 以總體聚合反應證實活性自由基迷你乳化聚合反應得到的產物具有活性。在迷你乳化共聚合反應的應用方面，研究內容記錄在附錄A，是以SDS與HD為界面穩定劑與共同安定劑，KPS為起始劑，在75oC或85oC，進行EHA、BA或MMA的迷你乳化共聚合反應，獲得安定的乳液，與傳統的乳化共聚合反應比較，迷你乳化共聚合反應的轉化率較高，反應產生的結塊殘渣較少，這可歸因於迷你乳化共聚合反應的獨特油滴成核機制，因此迷你乳化共聚合反應具有潛在優勢，可應用在工業生產。

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.