- 學位論文
可逆鏈轉移劑的電子效應對活性自由基聚合反應的影響
Studies of the Living Free-Radical Polymerization Reactions in the presence of Reversible Addition-Fragmentation chain Transfer Agents: Electronic Effect
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摘要
具有特殊功能的高分子材料為相關產業例如光電及生醫產業所急需。而高分子材料性能的掌握與控制高分子結構，諸如聚合度、分子量分佈(<1.5)與聚合物組成及分佈有極大的關係。傳統的活性陽離子與活性陰離子聚合技術，雖然能夠有效控制部份單體聚合物的聚合度，並使其分子量分佈較為窄小，但是其調整聚合物組成的能力有限，且其可聚合單體種類畢竟不多，再加上其嚴苛的反應條件都限制了此類技術在相關產業的廣泛使用。為了克服此項問題，近數年來國外學界及產業界積極投入研發活性自由基聚合法，以期能以較溫和或成本較低的方法開發出更多各類新穎高分子材料，以應市場所需。 本論文開發三種新穎的dithioester如C6H5CS2CH2R（1a），CF3C6H4CS2CH2R（1b）和CH3OC6H4CS2CH2R（1c）做為可逆鏈轉移劑(reversible addition-fragmentation chain transfer (RAFT) agent)，有效的控制acrylate系單體如(t-Butyl acrylate (tBA)或methyl acrylate (MA))之自由基聚合反應，達到似活性自由基聚合反應，其數目平均分子量與轉化率成正比，具有”living”的性質，且分子量分佈(Mw/Mn) < 1.3。本論文實驗結果發現帶有強烈推電子基的dithioester之聚合反應較為快速；又得聚合物PtBA的反應速率較PMA為快，可能為tBA的立體效應大，造成反應較快速。由於此觸媒系統可聚合的單體多樣化和其”living”性質，因此成功合成無規(random)和嵌段(block)共聚合的合成技術，其中無規共聚物poly(tBA-co-MA)，分子量(Mn)< 60000，分子量分佈(Mw/Mn)< 1.3；嵌段共聚物poly(tBA-b-AN)，極性單體含量> 50 %，分子量分佈< 1.5，據文獻資料搜尋結果此類嵌段共聚物尚未被研究。
並列摘要
Living free radical polymerization plays a crucial role in preparing well-defined polymeric materials owing to its mild reaction conditions, compatibility with different monomers, and high tolerance to impurities, water and functional groups. Significant progress has been made in several areas including nitroxide-mediated stable free radical polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition-fragmentation chain transfer polymerization (RAFT). Compared to ATRP and NMP, the RAFT process has the advantage of controlling polymerization of a wider range of monomers including acrylic acid and vinyl acetate. The RAFT process is mainly involved with the use of suitable thiocarbonylthio compounds of general structure Z-C(=S)S-R as a reversible addition-fragmentation chain transfer agent (RAFT agent) in a otherwise conventional radical polymerization. We have successfully synthesized three RAFT-agents with their Z-group containing substituents of different electronic effect in a process of simple purification and high yield. We found out that the polymerization of acrylates such as t-butyl acrylate and methyl acrylate is significantly influenced by the Z-group of different electronic effect. The reaction rate is faster for the Z-group containing an electron donating substituent with its resulting polymer maintaining a narrow molecular weight distribution.
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