Double metal cyanide (DMC) complexes, prepared by the reaction of K_3[Co(CN)_6]_2 and ZnCl_2 in the presence of complexing reagents, are well-known catalyst for the polymerization of epoxides and the synthesis of propylene oxide based polyether polyols (PPG) which are used in a wide range of polyurethane applications. The catalyst was originally discovered by General Tire Inc. in the 1960s. MMC catalyst was revisited starting in the middle of 1980's, with improvements made by some companies - including ARCO, Shell, and Asahi Glass. Recent improvements have made DMC catalysts much more attractive for commercial manufacture of polyether polyols. Compared to conventional KOH catalysts, DMC catalysts give high-quality PPG products that have low level of unsaturation, narrow molecular weight distribution, and low viscosity. While DMC catalysts offer significant advantages, unlike KOH, DMC catalysts must normally be activated over 2 h before the epoxide can be added continuously to the reactor at high temperature (> 100°C). Usually, a polyol initiator (or starter) and a DMC catalyst are combined and heated under vacuum prior to the addition of a small proportion of monomer. Long initiation time, say several hours, increases cycle time, which undercuts the economic advantage of faster polymerizations. In addition, heating the catalyst for a prolonged period at high temperature above 100°C can reduce its activity or deactivate it completely. In order to solve this problem we have prepared a series of new catalysts employing multi-metals, K_3[Co(CN)_6]_2, K_4Fe(CN)_6 and ZnCl_2, and investigated the kinetics of polymerization of PO. The properties of MMC-catalyzed PPG and polyurethane elastomer produced by using resulting PPG are also investigated and compared to those of conventional PPG produced by KOH catalyst.
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