环境友好与快速高效的可见光活化室温水溶液RAFT聚合
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摘要
可逆加成断裂链转移自由基聚合(RAFT聚合),集自由基聚合和活性聚合方法的优势于一体,备受关注。正发展成为制备结构精确聚合物的强有力工具。室温条件下水溶液活性自由基聚合研究有着重要的学术价值和潜在的应用前景。本论文探索并实现了在水溶液中可见光照下快速高效和活性可控的室温水溶液RAFT聚合。考察了S-乙基-S '-(α,α'-二甲基-α"-乙酸基)三硫代碳酸酯(EDMAT)链转移剂的紫外可见吸收光谱。考察了在30 oC和可见光照下,不同水溶液pH中EDMAT的稳定性。研究了可见光活化聚乙二醇单甲醚丙烯酸酯(PEGA)单体的室温水溶液RAFT聚合反应特征。通过2-羟乙基丙烯酸酯(HEA),N-(丙烯酰氧乙基)吡咯烷酮(NAP)的可见光活化室温水溶液RAFT聚合,考察了该聚合方法的单体普适性,并研究了可见光活化室温水溶液RAFT聚合的热活化效应。通过一个周期性的光开关过程,研究了可见光对该聚合反应的作用。研究结果表明,链转移剂EDMAT在可见波段存在一个弱吸收,使聚合反应的可见光活化成为可能。碱性或中性条件下,EDMAT水解,而偏酸性条件下其水解反应则明显抑制。在偏酸性的水溶液中,可见光活化室温RAFT聚合反应具有快速高效和活性可控的特点。而且,该聚合反应具有良好的单体普适性。低温下(7 oC)的聚合反应与室温下(25 oC)聚合反应的反应动力学特征相类似,体现出相同的引发期和聚合反应速率,说明该聚合反应在室温下的热活化效应可以忽略。周期性的可见光开关导致了该聚合反应周期性的快速启动和终止。聚合反应引发期过后,停止光照,则聚合反应终止。说明体系中的活性自由基浓度极低,绝大多数以中间体自由基形式存在。再次光照导致一个与前一光照时期相同的快速聚合反应过程,说明可见光明显加速了中间体自由基的断裂反应,使反应体系的活性自由基浓度明显提高。以上实验结果表明,可见光不仅促使TPO光解产生初级自由基,引发聚合反应,同时还兼具活化中间体自由基断裂反应的功能。这一特异的光开关控制过程可用于聚合反应的实时启动和终止。
Reversible Addition Fragmentation chain Transfer radical polymerization or RAFT polymerization has got much attention since its discovery. It has become a powerful technique for the synthesis of well-defined polymers or copolymers with both low polydispersity and functionalized end groups. From both academic and industrial standpoints, it is desirable to develop a rapid and well-controlled RAFT polymerization under mild aqueous conditions. This thesis describes the RAFT polymerization of acrylic monomers, including poly(ethylene glycol) methyl ether acrylate (PEGA), N-(2-acryloyloxyethyl) pyrrolidone (NAP), 2-hydroxyethyl acrylate (HEA) in acidic aqueous solution under mild visible light radiation at 25 oC. The thermo-activating effect of this aqueous RAFT polymerization was investigated. A periodic light-on-off process was employed for this aqueous RAFT polymerization to investigate the effect of visible light. The experimental results demonstrate that EDMAT exhibits an absorption covering a wide visible light wave range of 388-520 nm, which makes it possible that this RAFT polymerization may be accelerated by the visible light. This chain transfer agent is stable in acidic aqueous solution, but liable to hydrolysis in alkali or neutral solution. This RAFT polymerization proceeds rapidly and well-controlled in acidic aqueous solution at 25 oC, simply upon radiation with visible light. The kinetic character of this RAFT polymerization at 7 oC is quite similar to what observed at 25 oC, which also proceeded rapidly and keeping living character. This suggests the negligible thermo-activating effect of this aqueous RAFT polymerization. A periodic light-on-off process leads to a corresponding repeatable periodic polymerization-on-off process. The essentially polymerization-standstill state in the light-off period indicated the negligible concentration of active radicals and the significantly slow intermediate fragmentation reaction. Further turning on this visible light leads to another rapid polymerization process with the same kinetic character as what observed in the former light-on process. This suggests that the intermediate fragmentation reaction of this aqueous RAFT polymerization was significantly activated upon radiation with this visible light.
Reversible Addition Fragmentation chain Transfer radical polymerization or RAFT polymerization has got much attention since its discovery. It has become a powerful technique for the synthesis of well-defined polymers or copolymers with both low polydispersity and functionalized end groups. From both academic and industrial standpoints, it is desirable to develop a rapid and well-controlled RAFT polymerization under mild aqueous conditions. This thesis describes the RAFT polymerization of acrylic monomers, including poly(ethylene glycol) methyl ether acrylate (PEGA), N-(2-acryloyloxyethyl) pyrrolidone (NAP), 2-hydroxyethyl acrylate (HEA) in acidic aqueous solution under mild visible light radiation at 25 oC. The thermo-activating effect of this aqueous RAFT polymerization was investigated. A periodic light-on-off process was employed for this aqueous RAFT polymerization to investigate the effect of visible light. The experimental results demonstrate that EDMAT exhibits an absorption covering a wide visible light wave range of 388-520 nm, which makes it possible that this RAFT polymerization may be accelerated by the visible light. This chain transfer agent is stable in acidic aqueous solution, but liable to hydrolysis in alkali or neutral solution. This RAFT polymerization proceeds rapidly and well-controlled in acidic aqueous solution at 25 oC, simply upon radiation with visible light. The kinetic character of this RAFT polymerization at 7 oC is quite similar to what observed at 25 oC, which also proceeded rapidly and keeping living character. This suggests the negligible thermo-activating effect of this aqueous RAFT polymerization. A periodic light-on-off process leads to a corresponding repeatable periodic polymerization-on-off process. The essentially polymerization-standstill state in the light-off period indicated the negligible concentration of active radicals and the significantly slow intermediate fragmentation reaction. Further turning on this visible light leads to another rapid polymerization process with the same kinetic character as what observed in the former light-on process. This suggests that the intermediate fragmentation reaction of this aqueous RAFT polymerization was significantly activated upon radiation with this visible light.
引文
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[4] Moad, G.; Rizzardo, E.; Thang, S. H. Toward Living Radical Polymerization [J]. Acc. Chem. Res. 2008, 41:1133-1142.
[5] Moad, G.; Rizzardo, E.; Thang, S. H. Radical addition–fragmentation chemistry in polymer synthesis [J]. Polymer 2008, 49: 1079-1131.
[6] Barner-Kowollik, C.; Perrier, S. The future of reversible addition fragmentation chain transfer polymerization [J]. J. Polym. Sci. Polym. Chem. 2008, 46: 5715-5723
[7] Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Jeffery, J.; Le, T. P. T.; Mayadunne, R. T. A.; Meijs, G. F.; Moad, C. L.; Moad, G.; Rizzardo, E.; Thang, S. H. Living Free-Radical Polymerization by Reversible Addition-Fragmentation Chain Transfer: The RAFT Process [J]. Macromolecules 1998, 31: 5559-5562.
[8] Chong, Y. K.; Le, T. P. T.; Moad, G.; Rizzardo, E.; Thang, S. H. A More Versatile Route to Block Copolymers and Other Polymers of Complex Architecture by Living Radical Polymerization: The RAFT Process [J]. Macromolecules 1999, 32: 2071-2074.
[9] Shim, S. E.; Jung, H.; Lee, H.; Biswas J.; Choe, S. Living Radical Dispersion Photopolymerization of Styrene by a Reversible Addition–Fragmentation Chain Transfer (RAFT) Agent [J]. Polymer 2003, 44: 5563-5572.
[10] Quinn, J. F.; Barner, L.; Rizzardo, E.; Davis, R. P. Living Free-radical Polymerization of Styrene under a Constant Source ofγ-Radiation [J]. J. Polym. Sci. Part A: Polym. Chem. 2002, 40: 19-25.
[11] You, Y. Z.; Hong, C. Y.; Bai, R. K.; Pan, C.Y.; Wang, J. Photo-Initiated Living free Radical Polymerization in the Presence of Dibenzyl Trithiocarbonate [J]. Macromol. Chem. Phys. 2002, 203: 477-483.
[12] Chen, G.; Zhu, X.; Zhu, J.; Cheng, Z. Plasma-Initiated Controlled/Living Radical Polymerization of Methyl Methacrylate in the Presence of 2-Cyanoprop-2-yl 1-dithionaphthalate (CPDN) [J]. Macromol Rapid Comnum. 2004, 25: 818-824.
[13] Zhu, J.; Zhu, X.; Zhang, Z.; Cheng, Z. Reversible addition-fragmentation chain transfer polymerization of styrene under microwave irradiation [J]. Polym Sci Part A: Polym Chem 2006, 44(23):6810–6816.
[14] Zhang, Z.; Zhu, X.; Zhu, J.; Cheng, Z.; Zhu, S. Thermal-initiated reversible addition-fragmentation chain transfer polymerization of methyl methacrylate in the presence of oxygen [J]. Polym Sci Part A: Polym Chem 2006, 44(10): 3343–3354.
[15] Quinn, J. F.; Rizzardo, E,; Davis, T. P. Ambient temperature reversible addition–fragmentationchain transfer polymerisation [J]. Chem Commun 2001, 1044-1045.
[16] Convertine, A. J.; Ayres, N.; C. Scales, W.; Lowe, A. B.; C. McCormick, L.; Facile, Controlled, Room-Temperature RAFT Polymerization of N-Isopropylacrylamide [J]. Biomacromolecules 2004, 5:1177-1180.
[17] Convertine, A. J.; Lokitz, B. S.; Lowe, A. B.; Scales, C. W.; Myrick, L. J.; McCormick, C. L. Aqueous RAFT Polymerization of Acrylamide and N,N-Dimethylacrylamide at Room Temperature [J]. Macromol Rapid Commun 2005: 791-795.
[18] Convertine, A. J.; Lokitz, B. S.; Vasileva, Y.; Myrick, L. J.; Scales, C. W.; Lowe, A. B.; McCormick, C. L. Direct Synthesis of Thermally Responsive DMA/NIPAM Diblock and DMA/NIPAM/DMA Triblock Copolymers via Aqueous, Room Temperature RAFT Polymerization [J]. Macromolecules 2006, 39: 1724-1730.
[19] You, Y.; Hong, C.; Bai, R.; Pan, C.; Wang, Photo-Initiated Living Free Radical Polymerization in the Presence of Dibenzyl Trithiocarbonate [J]. Mocromol Chem Phys. 2002, 203(3): 477-483.
[20] Quinn, J. F.; Davis, T. P.; Barner, L.; Barner-Kowollik, C. The application of ionizing radiation in reversible additione-fragmentation chain transfer (RAFT) polymerization: Renaissance of a key synthetic and kinetic tool [J]. Polymer 2007, 48: 6467-6480.
[21] Quinn, J. F.; Barner, L.; Barner-Kowollik, C.; Rizzardo, E.; Davis, T. P. Reversible Addition-Fragmentation Chain Transfer Polymerization Initiated with Ultraviolet Radiation [J]. Macromolecules 2002, 35: 7620-7627.
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