Heterotrimetallic Carbon Dioxide Copolymerization and Switchable Catalysts: Sodium is the Key to High Activity and Unusual Selectivity

Alex J Plajer,Charlotte K Williams

doi:10.1002/ange.202101180

Abstract

AbstractA challenge in polymer synthesis using CO2 is to precisely control CO2 placement in the backbone and chain end groups. Here, a new catalyst class delivers unusual selectivity and is self‐switched between different polymerization cycles to construct specific sequences and desirable chain‐end chemistries. The best catalyst is a trinuclear dizinc(II)sodium(I) complex and it functions without additives or co‐catalysts. It shows excellent rates across different ring‐opening (co)polymerization catalytic cycles and allows precise control of CO2 incorporation within polyesters and polyethers, thereby allowing access to new polymer chemistries without requiring esoteric monomers, multi‐reactor processes or complex post‐polymerization procedures. The structures, kinetics and mechanisms of the catalysts are investigated, providing evidence for intermediate speciation and uncovering the factors governing structure and composition and thereby guiding future catalyst design.

Highlights

Carbon dioxide utilization is essential to add value to and recycle wastes; when it is effectively coupled with sequestration and storage it has potential for significant reductions in greenhouse gas emissions.[1,2,3] Society urgently needs these utilization technologies but the fundamental science is underdeveloped and lacks viable products
The catalyst is unusual because it allows for control over the placement and formation of poly(carbonate), -ester, and -ether linkages, the latter are beneficial end-groups for product stability
It is switched between three different catalytic cycles providing a straightforward and highly practical route to make new polymer compositions

Summary

Introduction

Angewandte Chemie International Edition published by Wiley-VCH GmbH Overall fraction of CO2 taken up could effectively moderate polymer physical-chemical properties without requiring any changes to the monomers, polymerization processes or catalysts. Such controllable catalysis should allow other monomers, such as anhydrides, which are known to copolymerize with epoxides, to be efficiently localized within the polymer backbone.[14,15] Chains featuring oligoether end groups would be especially desirable to overcome a problematic instability of carbon dioxide derived polycarbonates.

Results and Discussion

Conclusion

Conflict of interest