Biased Lewis Pairs: A General Catalytic Approach to Ether‐Ester Block Copolymers with Unlimited Ordering of Sequences. (18th September 2019)

• Record Type: Journal Article
• Authors: Liu, Shan; Bai, Tianwen; Ni, Kang; Chen, Ye; Zhao, Junpeng; Ling, Jun; Ye, Xiaodong; Zhang, Guangzhao
• Is Part Of: Angewandte Chemie. Volume 131:Number 43(2019)
• Page Start: 15624
• Page End: 15633
• Publication Date: 2019-09-18
• Subjects: Chemoselektivität -- Lewis-Säuren -- Organokatalyse -- Polymere -- Ringöffnung; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.201908904
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: 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. Abstract : Ein metallfreies Katalysatorsystem bestehend aus einer Lewis‐Säure und einer Lewis‐Base ermöglicht die selektive Polymerisation von gemischten Epoxiden und cyclischen Estern. Das Verfahren überwindet bestehende Limitierungen bezüglich der Reihenfolge der Verkettung der beiden Monomertypen und erlaubt die sequenzgesteuerte Synthese von Blockcopolymeren vom Ether‐Ester‐Typ.