Polymerizations of propylene oxide have been carried out by using double metal cyanide (DMC) catalyst prepared by reacting ZnCl2 and K-3 [Co(CN)(6)](2) in the presence of complexing agents and multi-metal cyanide (MMC) catalyst prepared by reacting ZnCl2, K-3 [Co(CN)(6)](2) and K4Fe(CN)(6)) in the presence of complexing agents. The catalysts were characterized by X-ray photoelectron spectroscopy, infrared spectroscopy and X-ray powder diffraction. By controlling the type of complexing agent and metal, and by controlling polymerization parameters, the catalytic activity, initiation time and the unsaturation level of poly(oxy propylene) could be tuned. Both DMC and MMC catalysts showed very high activities, and the MMC catalyst showed high activity in a wide range of temperature (30-130degreesC). The POPs obtained by the DMC catalyst and the MMC catalysts were characterized by ultra-low level of unsaturation (0.002-0.01 meq/g) and by polydispersity (MWD = 1.02-1.10). The active sites of DMC-catalyzed polymerization of propylene oxide had both cationic and coordinative characters. (C) 2004 Elsevier B.V. All rights reserved.