Preparation of Double-Metal Cyanide Catalysts containing Zn-OAc moiety for Propylene Oxide/CO2 Copolymerization

Abstract

Zn and Co-based double metal cyanide (DMC) catalysts are frequently employed in polyether polyol production utilizing the ring opening polymerization for epoxide. When pressurized with CO2 during the reaction, these catalysts have the ability to incorporate CO2 into polyol chains, presenting DMC as a potential frontrunner in Carbon Capture and Utilization (CCU) technology. However, it has been challenging to find catalysts that maintain high activity under high pressure of CO2 gas, produce minimal cyclic carbonate byproducts, and have a significant CO2 incorporation ability. In this study, our team innovated a synthesis method for Zn-OAc containing catalysts, capable of fulfilling all these criteria. This technique also permits the inclusion of Zn-Cl and Zn-OtBu units, which vary with the stoichiometry of the reactants. These catalysts were analyzed using NMR, SEM-EDS, XRD, ATR-FTIR, and ICP-OES instruments. It was observed that in Propylene Oxide/CO2 copolymerization, the higher the Zn-OAc portion ratio, the greater the CO2 content in the polymer. Notably, the Zn-OAc/OtBu(0.95/0.08) catalyst, which contains a slight amount of Zn-OtBu moiety which is effective in suppressing byproduct formation yet producing high molecular weight impurities, demonstrated a performance, the turnover frequency (TOF) of 64,000 PO-consumption/Co/h and 20,000 CO2-consumption/Co/h with cyclic carbonate at a level of 3.4 wt%, making it a viable candidate for commercial application.