Double metal cyanide complex (DMC) catalysts, widely used industrially for the ring-opening polymerization (ROP) of propylene oxide (PO), have garnered attention for PO/CO2 copolymerization due to their ease of preparation and high catalytic activity, although their ability to incorporate CO2 remains relatively limited. In this study, we report DMC variants with well-defined compositions, specifically incorporating ZnOAc and ZnOtBu components. These catalysts were synthesized via a distinct route from conventional DMCs by reacting K3Co(CN)6 with 2 eq. Zn(OAc)2, followed by sequential treatment with HCl and LiOAc. Among the variants, the DMCs enriched in ZnOAc and minimized in ZnOtBu content-e.g., ZnOAc1.28ZnOtBu0.10ZnCl0.02Zn0.80Co(CN)6H2O4-exhibited outstanding productivity (up to 5.0 kg g-cat-1 h-1) and enhanced CO2 incorporation (FCO2, up to 0.56), yielding poly(ether-co-carbonate) diols with Mn ≈ 3500 Da and narrow dispersity (Mw/Mn = 1.7). SEM images revealed thin plate-like structures with straight lines, resembling laterally fused planks. By correlating the known atomic-level structure of ZnOAcZnCo(CN)6H2O4 with the SEM images, the high performance was reasonably attributed to fractures along the straight lines, which expose the lateral faces of thin planks bearing syn-anti Zn-OC(O-Zn)CH3 units with Zn-Zn distances of 4.4 Å. These structural features are well-suited to facilitate a bimetallic polymerization mechanism, as proposed for other catalyst systems.
Park et al. (Wed,) studied this question.