Double metal cyanide catalyst prepared using H3Co(CN) 6 for high carbonate fraction and molecular weight control in carbon dioxide/propylene oxide copolymerization

Abstract

Simple mixing of H3Co(CN)6 and ZnCl2 in methanol resulted in precipitates of [ZnCl]+2[HCo(CN) 6]2-, constituting a new type of double metal cyanide (DMC) catalyst exhibiting a high performance in carbon dioxide (CO2)/propylene oxide (PO) copolymerization. High-molecular-weight poly(propylene carbonate-co-propylene oxide)s [poly(PC-co-PO)s] (Mn∼40,000) were consistently obtained with high carbonate fractions (∼60 mol %) and a high selectivity (>95%) with the new type of DMC catalyst. Conventional preparation of the DMC catalyst using K3Co(CN)6 and ZnCl2 required removing KCl through thorough washing and resulted in lower carbonate fractions (10-40 mol %), which depended on the washing conditions. Feeding hydrophobic diols such as 1,10-decanediol as chain transfer agent preserved the high carbonate fraction (∼60%) and enabled precise control of the molecular weight, including preparation of a low-molecular-weight poly(PC-co-PO)-diol (Mn ∼2000), which was a flowing viscous liquid with a low Tg (-30°C) suitable for polyurethane applications. © 2013 Wiley Periodicals, Inc.