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Living cationic ring-opening polymerization of 2-oxazolines initiated by rare-earth metal triflates

机译：稀土金属三氟甲磺酸酯引发的2-恶唑啉活性阳离子开环聚合

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摘要

The cationic ring-opening polymerization (CROP) of substituted 2-oxazolines using rare-earth metal triflates (RE(OTf)(3)) as initiator was investigated for the first time. In this work, we examined the polymerization characteristics of 2-ethyl-2-oxazoline (EtOx) initiated by Sc(OTf)(3) under conventional thermal heating and microwave irradiation, and compared the respective outcomes with those obtained with the most frequently used initiator methyl tosylate (MeOTs). The results indicated that Sc(OTf)(3) exhibits a higher catalytic efficiency to the EtOx polymerization than MeOTs under identical conditions. The controlled/living nature of the Sc(OTf)(3)-catalyzed CROP was confirmed by its linear first-order kinetics and the narrow molecular weight distribution of the resultant polymers as well as the block copolymerization of EtOx and 2-phenyl-2-oxazoline (PhOx). Based on in situ NMR spectroscopic studies and SEC analysis of PEtOx samples obtained from the control termination experiments, a possible initiating/propagating mechanism has been proposed for the living cationic ring-opening polymerization. Morever, this rare-earth catalytic system can also be applied to the ring-opening polymerization of some sterically hindered or aryl-substituted 2-oxazolines.
机译：首次研究了以稀土金属三氟甲磺酸酯（RE（OTf）（3））为引发剂的取代2-恶唑啉的阳离子开环聚合（CROP）。在这项工作中，我们研究了Sc（OTf）（3）在常规热加热和微波辐射下引发的2-乙基-2-恶唑啉（EtOx）的聚合特性，并将各自的结果与最常用的结果进行了比较。引发剂甲苯磺酸甲酯（MeOTs）。结果表明，在相同条件下，Sc（OTf）（3）比MeOTs对EtOx聚合的催化效率更高。 Sc（OTf）（3）催化的CROP的线性/一级动力学和所得聚合物的窄分子量分布以及EtOx和2-苯基-2的嵌段共聚证实了其控制/活性。 -恶唑啉（PhOx）。基于原位NMR光谱研究和从控制终止实验获得的PEtOx样品的SEC分析，提出了一种可能的引发/传播机制，用于活性阳离子开环聚合。此外，该稀土催化体系也可用于一些空间位阻或芳基取代的2-恶唑啉的开环聚合。

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