Multi-metal cyanide catalysts for ring-opening polymerization of propylene oxide

Polymerizations of propylene oxide (PO) have been carried out by using a series of multi-metal metal cyanide (MMC) catalysts prepared by reacting ZnCl2 and K3[Co(CN)6]2, K4Fe(CN)6, K3Fe(CN)6 and/or K2Ni(CN)4 in the presence of tert-butyl alcohol and polytetramethylene ether glycol as complexing agents. The resulting MMC catalysts are characterized by elemental analysis, X-ray photoelectron spectroscopy, infrared spectroscopy and X-ray powder diffraction. The structure of MMC catalysts with broadened X-ray diffraction peaks is different from that of highly crystalline Prussian blue analogues of microporous crystalline materials due to the coordination of complexing agents. The PO polymerization behavior was tunable by changing with various metal cyanide salts after fixing a main catalyst component as ZnCl2. Even if the basic structure of the MMC complexes is different each other, i.e. orthorhombic for Zn2[Fe(CN)6] and monoclinic for Zn3[Fe(CN)6]2 and Zn3[Co(CN)6]2, the chemical formulations become more complicated by forming MMC complexes through cyano bridges and complexing agents’ coordination and the structure more distorted from the defined crystal structures. All catalysts prepared by using K3[Co(CN)6]2 showed very high activity once they were activated. Simply changing catalyst formulation by choosing different metal cyanide salts, catalytic activity, induction period, polymer molecular weight and its distribution and polymer viscosity could be tuned.