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Scheme 4 Possible mechanism of MMA polymerization mediated by Alane/NHO Lewis pair
LBOR
O
OR
OLA
LA
LBO
OR
O
n−1
[LA-OR-LA]
LB OR
O
OR
OLA
n
LBO
OR
O
OR
LA
O
OR
n
LA
OLBO
OR
O
n−1
OR
LB OR
O
OR
OLA
n+1
Kinetically
favored
back- biting
Propagation
M
Thermodynamically
favored
back- biting
OR
O
n−1
CO2R
Termination (a)
CO2R
CO2R
+ [ M→LA ] + [ M→LA ]
Termination (b)
[LA-OR-LA]
−
− −
−
−
−
+
+
+ +
++
Scheme 5 Proposed two possible backbiting chain-termination pathways competed withchain propagation cycles in the polymerization of MMA by the LP (Reprinted withpermission from Ref.[29]; Copyright (2014) American Chemical Society)
Fig. 4 (a) MALDI-TOF MS spectrum of the low-MWPMMA sample produced by (BHT)2AlMe/NHO4; (b) Plotof m/z values from spectrum versus the number of MMArepeat units (n) (Reprinted with permission from Ref.[50];Copyright (2018) American Chemical Society)
Fig. 5 GPC traces of homopolymer (black), diblockcopolymer (red), and ABA triblock copolymer (blue)produced from the sequential block copolymerization ofMMA and BnMA by (BHT)2AlMe/NHO4 in toluene at RT:(a) polymerizing MMA first; (b) polymerizing BnMA first(Reprinted with permission from Ref.[50]; Copyright(2018) American Chemical Society) (The online version iscolorful.)
Fig. 6 GPC traces of (a) PMMA produced byIAP3/(BHT)AliBu2 LP at various [MMA]0/[IAP3]0/[(BHT)AliBu2]0 ratios at RT. Conditions: [MMA]0/[IAP3]0/[(BHT)AliBu2]0 = 400:1:2, 800:1:2, 1600:1:2,3200:1:2, 6400:1:2, 10000:1:2, 15000:1:2, and 20000:1:2,[MMA]0 = 0.936 mol L−1 and (b) PMMA samples obtainedfrom chain extension experiments in toluene at RT,[MMA]0 = 0.47 mol L−1 and (c) homopolymer (black),diblock copolymer (red), and ABA triblock copolymer(blue) produced from the sequential block copolymerizationof MMA and EMA by IAP3/(BHT)AliBu2 in toluene at RT:polymerizing MMA first, [MMA]0 = 0.936 mol L−1
(Reprinted with permission from Ref.[58]; Copyright(2018) John Wiley & Sons Inc) (The online version iscolorful.)
20 24 28Retention time (min)
A: [2(BHT)AliBu2 + 400MMA] + IAP3
B: [2(BHT)AliBu2 + IAP3] + 400MMA
Fig. 7 GPC traces of PMMA obtained from thepolymerization performed using different activationprocedures (Reprinted with permission from Ref.[58];Copyright (2018) John Wiley & Sons Inc)
12 16 20 24 28Retention time (min)
400MMA-24h-400MMA800MMA
Fig. 8 GPC traces of PMMA produced from theIAP3/(BHT)AliBu2-catalyzed polymerization of MMA in a800[MMA]0/2(BHT)AliBu2/[IAP3]0 ratio (red) and fromIAP3/(BHT)AliBu2-catalyzed chain extension experimentsof two batch of 400 equiv. of MMA after thepolymerization of the first batch of MMA reach fullmonomer conversion and kept at RT for 24 h (black)(Reprinted with permission from Ref. [58]; Copyright(2018) John Wiley & Sons Inc) (The online version iscoloful.)
3 期 白云等:Lewis酸碱对催化极性乙烯基单体聚合 243
优良的活性聚合特征也将在高分子合成领域得以
发展. 通过对聚合单体的扩展,利用LPP的多嵌段
聚合能力,LPP体系有望在聚合物弹性体[68, 69]、
原位聚合自组装[70]、超分子聚合物的合成[71]等领
域得以应用. 最后,希望本专论能给LPP相关领域
的科研工作者带来帮助,也希望引起更多科研工
作者对LP催化聚合研究的兴趣.
作者简介:张越涛,男,1977年出生. 1995 ~ 2004年于吉林大学化学系获得学士、硕士、博
士学位,并于同年留校工作. 2006年赴美国科罗拉多州立大学从事博士后研究. 2009年于美国
科罗拉多州立大学化学系,任职research scientist II. 2013年入选第四批国家“青年千人计
划”,同时受聘吉林大学教授,博士生导师. 2014年获得国家自然科学基金委“优秀青年基
金”. 现从事基于可再生资源高分子的催化合成(可持续发展聚合物的催化合成),非食物生物
质降解成高附加值化学品或生物质能源的研究,经典或受阻Lewis酸碱对在聚合物合成中的
应用,金属有机、卡宾或有机硅催化乙烯基极性单体的活性可控聚合,及小分子C―H键活
化等工作.
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Polymerization of Polar Vinyl Monomers Catalyzed by Lewis Pairs
Yun Bai, Yue-tao Zhang*
(College of Chemistry, State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun 130012)
Abstract The field of the “frustrated Lewis pair” (FLP) chemistry has been receiving sustained intense interestsever since the seminal work reported by Stephan and Erker. On the one hand, the application of FLPs has nowbeen well established in the small molecule chemistry, such as the activation of small molecules, catalytichydrogenation reactions, and new reactivity/reaction developments. On the other hand, Lewis pair polymerization(LPP) has emerged as the hotspot and frontier of polymer synthesis and generated some exciting results inpolymer synthesis, especially in the polymerization of various polar vinyl monomers. Although the polymerizationpromoted by LPs, either FLPs or classical Lewis adducts (CLAs), exhibited high activity for polymerization ofpolar vinyl monomers, the application of such polymerization is hampered by both the low initiation efficienciesand chain-termination side reactions, evidenced by the much higher obtained number-average molecular weight(Mn) than the calculated Mn and broader molecular weight distribution (MWD, or large Đ values) of the resultingpolymers, thus giving rise to low initiation efficiencies (I*) and rendering the inability to produce well-definedblock copolymers. Therefore, it remains as a challenge to achieve the living polymerization of polar vinylmonomers by a non-interacting, true FLP, or LP-promoted living polymerization of less bulky methacrylates,particularly methyl methacrylate (MMA), a very important fundamental monomer in the polymer industry. Herein,we summarized the recent developments achieved in the polar vinyl monomer polymerization by LPP since thefirst successful polymerization catalyzed by LP in 2010, including the scopes of monomers, investigation ofreaction mechanism, and different polymerization catalyst systems based on classic Lewis acid-base adduct (CLA)or FLP. These results indicated that the synergistic effects of the LA and LB sites of LPs were essential to achievean effective and controllable polymerization system. By choosing appropriate combination of Lewis acid andLewis base, not only the living polymerization of polar vinyl monomer could be achieved, but also the synthesis ofultrahigh molecular weight polymer with Mn > 106 g mol−1 and narrow MWD was obtained through this FLPpolymerization strategy. Last but not least, with the aim to push forward the studies on LPP, more attention shouldbe paid by chemists from but not limited to the field of frustrated Lewis pairs chemistry for the developing andenriching polymer synthesis by LPP.Keywords Lewis pair polymerization (LPP), Frustrated Lewis pair (FLP), Polar vinyl monomer, Livingpolymerization, Ultrahigh molecular weight, Catalysis