The kinetics of propylene oxide polymerization catalyzed by double metal cyanide complexes was studied by means of pressure measurements. The induction periods were determined as the time as the system pressure began to drop and the reaction rates were considered proportional to the slope of pressure decrease. The induction periods were found to depend on reaction temperature, water content and the type and amount of catalysts, regulators, and solvents. Elevating reaction temperatures, using dried raw materials, and applying proper regulators favored shortened induction periods. The reaction rates were found to depend on the concentrations of catalyst C, monomer M, and regulator Tr as expressed in the equationR-p = (KMC)-C-2 / (1 + kTr),where K was a rate constant and k was a transition constant. The rates also depended on reaction temperature. The apparent activation energy was 59.1 kJ/mol according to the Arrhenius equation. A mechanism was proposed for the polymerization which was in good accordance with the experimental results. (C) 2004 Wiley Periodicals, Inc.