Liu Shan, Bai Tianwen, Ni Kang, Chen Ye, Zhao Junpeng, Ling Jun, Ye Xiaodong, Zhang Guangzhao
Faculty of Materials Science and Engineering, South China University of Technology, Guangzhou, 510640, P. R. China.
MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou, 310027, China.
Angew Chem Int Ed Engl. 2019 Oct 21;58(43):15478-15487. doi: 10.1002/anie.201908904. Epub 2019 Sep 18.
Polymerizing epoxides after cyclic esters remains a major challenge, though their block copolymers have been extensively studied and used for decades. Reported here is a simple catalytic approach based on a metal-free Lewis pair that addresses the challenge. When the Lewis acid is used in excess of a base, selective (transesterification-free) polymerization of epoxides occurs in the presence of esters, while selectivity toward cyclic esters is achieved by an oppositely biased catalyst. Hence, one-pot block copolymerization can be performed in both ester-first and ether-first orders with selectivity being switchable at any stage, yielding ether-ester-type block copolymers with unlimited ordering of sequences as well as widely variable compositions and architectures. The selectivity can also be switched back and forth several times to generate a multiblock copolymer. Experimental and calculational results indicate that the selectivity originates mainly from the state of catalyst-activated hydroxy species.
尽管环酯之后的环氧乙烷聚合几十年来已被广泛研究并应用，但其仍然是一项重大挑战。本文报道了一种基于无金属路易斯酸碱对的简单催化方法来应对这一挑战。当路易斯酸的用量超过碱时，在酯存在的情况下会发生环氧乙烷的选择性（无酯交换）聚合，而通过相反偏置的催化剂可实现对环酯的选择性。因此，一锅法嵌段共聚可以按酯优先和醚优先两种顺序进行，且选择性在任何阶段都可切换，从而得到具有无限序列排列以及广泛可变组成和结构的醚 - 酯型嵌段共聚物。选择性还可以来回切换几次以生成多嵌段共聚物。实验和计算结果表明，选择性主要源于催化剂活化的羟基物种的状态。
