Polymerizations of propylene oxide have been carried out by using double metal cyanide (DMC) catalysts based on Zn-3[Co(CN)(6)](2). By controlling the type and the amount of complexing agent during preparation of catalyst the catalytic activity, initiation time, and the unsaturation level in polyether polyols could be tuned. Various catalysts prepared by changing the complexing and co-complexing agents were characterized by x-ray photoelectron spectroscopy, infrared spectroscopy, and X-ray powder diffraction. Highly active catalyst prepared by choosing a polytetramethylene ether glycol as a co-complexing agent resulted in polyoxypropylenes (POP) with low very low unsaturation level (0.003-0.006 meq/g) and with narrow molecular weight distribution (MWD = 1.02-1.04). The active sites of DMC-catalyzed polymerization of propylene oxide have both cationic and coordinative characters. C-13 NMR analysis showed that the polyols have a random distribution of the configurational sequences and head-to-tail regiosequence, even if the amount of [rr] triad of polyol produced by DMC catalyst was larger than that of polyol by conventional KOH catalyst. The distortionless enhancement by polarization transfer analysis showed that there exist regioirregular sequences as well. The stress-strain curves of methylene diisocyanate/1,4-butanediol cured POP-based polyurethane elastomers showed that the unsaturation content contained in POP showed a dramatic effect on the mechanical properties. (C) 2003 Elsevier Science Ltd. All rights reserved.