Solvent Effects in Grafting-through Ring-Opening Metathesis Polymerization
Solvent Effects in Grafting-through Ring-Opening Metathesis Polymerization
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DOI：
10.1021/acs.macromol.2c00254
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发表时间：
2022-04-22
期刊：
影响因子：
5.5
通讯作者：
Matson, John B.
中科院分区：
文献类型：
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作者：
Blosch, Sarah E.;Alaboalirat, Mohammed;Matson, John B.
利用Grubbs第三代催化剂((H(2)IMes)(Cl)（2)(pyr)2RuCHPh）的开环复分解聚合（ROMP）表现出活性聚合的特征，包括分子量随着单体转化而增加，以及生成（多）嵌段共聚物的能力。然而，由于催化剂的分解，仍然会发生不可逆的终止反应，导致链终止，特别是在空间要求高的单体，如大单体（mm）的情况下。在这项工作中，我们在六种不同纯度的ROMP常用溶剂中对三种不同的mm进行了相同的ROMP反应。溶剂包括乙酸乙酯（EtOAc）、二氯甲烷（CH2Cl2）、氯仿（CHCl3）、甲苯、四氢呋喃（THF）和N，N-二甲基甲酰胺（DMF）。所有聚合均在空气瞄准下进行，瓶刷聚合物主聚合度（N-bb）为100。这三种mm均在α链端含有降冰片烯，分子量（M-n）为~ 4kg /mol。它们包括一个在ω链末端有一个溴的聚苯乙烯MM和两个在ω链末端有一个溴或三硫代碳酸盐基团的聚丙烯酸正丁酯MM。溶剂的选择，在某些情况下的纯度水平，导致这些ROMP接枝反应的繁殖速率的显著差异。在所测试的溶剂中，所有mm在EtOAc和CH2Cl2中的繁殖速度分别比在CHCl3、甲苯和THF中的繁殖速度快约4倍和2倍。聚苯乙烯MM在DMF中的传播速度比所有其他溶剂慢得多，与两种测试的聚丙烯酸正丁酯MM的慢溶剂相当。在某些情况下，溶剂的纯度对繁殖速率有深远的影响：在EtOAc的情况下，纯化导致繁殖速率降低2倍；相比之下，需要纯化THF才能观察到MM完全转化为瓶刷聚合物。omega链端官能团对ROMP速率没有影响。利用紫外可见光谱测量催化剂分解，这是ROMP中主要的聚合物终止途径，我们发现了显著的溶剂效应，其中催化剂在THF和DMF中的分解速度比在甲苯中的分解速度快10倍以上。最后，针对N-bb = 500或1000的研究表明，甲苯、EtOAc和CH2Cl2在ROMP中表现出最高程度的“活性”。这些结果将使利用ROMP合成具有高度活性的复杂聚合物结构成为可能。
Ring-opening metathesis polymerization (ROMP) utilizing Grubbs' third-generation catalyst ((H(2)IMes)(Cl)(2)(pyr)2RuCHPh) shows the characteristics of living polymerizations, including molecular weights increasing with monomer conversion and the ability to make (multi)block copolymers. However, irreversible termination reactions still occur due to catalyst decomposition, leading to terminated chains, especially in the context of sterically demanding monomers such as macromonomers (MMs). In this work, we performed identical ROMP reactions on three different MMs in six solvents commonly used in ROMP with varying levels of purity. The solvents included ethyl acetate (EtOAc), dichloromethane (CH2Cl2), chloroform (CHCl3), toluene, tetrahydrofuran (THF), and N,N-dimethylformamide (DMF). All polymerizations were conducted under air targeting a bottlebrush polymer backbone degree of polymerization (N-bb) of 100. All three MMs included a norbornene on the alpha chain end and had a molecular weight (M-n) of ~ 4 kg/mol. They included one polystyrene MM with a bromine on the omega chain end and two poly(n-butyl acrylate) MMs with either a bromine or a trithiocarbonate group on the omega chain end. Solvent choice, and in some cases the level of purity, led to significant differences in the propagation rate in these ROMP grafting-through reactions. Of the solvents tested, the propagation rates in EtOAc and CH2Cl2 were approximately 4-fold and 2-fold faster, respectively, than that in CHCl3, toluene, and THF for all MMs. Propagation was much slower in DMF for the polystyrene MM than all the other solvents and on par with the slower solvents for the two poly(n-butyl acrylate) MMs tested. The purity of the solvent in some cases had a profound effect on the propagation rate: In the case of EtOAc, purification led to a 2-fold decrease in propagation rate; in contrast, purification of THF was required to observe full conversion of a MM to a bottlebrush polymer. The functional group on the omega chain end did not influence the rate of ROMP. Utilizing UV-vis spectroscopy to measure catalyst decomposition, the main polymer termination route in ROMP, we uncovered dramatic solvent effects, where the catalyst decomposed over 10 times faster in THF and DMF than in toluene. Finally, studies targeting N-bb = 500 or 1000 revealed that toluene, EtOAc, and CH2Cl2 demonstrated the highest degree of "livingness " in ROMP. These results will enable the synthesis of complex polymer architectures using ROMP with a high degree of living character.