Modification of the Zn–Co double metal cyanide complex for the synthesis of carbon dioxide–derived poly(ether–carbonate) polyols

Abstract

The Zn–Co double metal cyanide (DMC) complex is regarded as a promising catalyst for the copolymerization of CO2 and propylene epoxide (PO). Various methods have been adopted to improve the catalytic performance of DMC. In this study, polyvinylpyrrolidone (PVP), as a co-complexing agent, was innovatively used to modify DMC and applied to the synthesis of poly(ether–carbonate) polyols from CO2, PO, and a chain transfer agent. The modified catalysts exhibited higher catalytic activity than the catalysts prepared by conventional methods, with a nearly 10 % increase in PO conversion. The most critical breakthrough was a reduction of nearly 5 wt% in the byproduct propylene–carbonate. The results confirmed that amide groups in PVP could coordinate with active center Zn2+, providing the modified catalysts with advantages such as low-symmetry structure, high specific surface area, and strong acidity. Moreover, the dual effects of PVP coordination and dispersion led to dramatic differences in the microstructure and activity of the catalysts when added during different preparation processes of DMC. The coordination effect of PVP was dominant in the nucleation stages which affected the crystal structure and morphology, whereas, the dispersion effect was dominant in the aging stages which prevented the catalyst particles from growing and thus a higher specific surface area. This is critical for paving the way towards exploring the introduction of groups with high steric hindrance into Zn–Co complex catalysts. In addition, a detailed and in-depth insight into the structure–activity relationship of DMC for poly(ether–carbonate) polyols synthesis was summarized.

Keywords

• Double metal cyanide catalyst
• Polyvinylpyrrolidone
• Carbon dioxide
• Propylene epoxide
• Poly(ether–carbonate) polyols