A double metal cyanide(DMC) complex based on Zn3[Co(CN)6]2 is prepared and it is characterized by IR

XRD

TGA．This catalytic system is highly active for the ring-opening polymerization (ROP) of propylene oxide

and gives polymers that have narrow MWD(＜1.40) and low unsaturation(＜0.014 meq／g)．The molecular weight of polymer is entirely controlled by reacted monomer to initiator molar ratio(M／I)．The polymers prepared with stepwise addition of monomer exhibit narrower MWD compared with those prepared by one-step addition of monomer．The polymerization involves a rapid exchange equilibrium between the active species and inactive chains． It has also been proved that chain termination of this catalytic system is reversible or temporary．The active centre of catalyst is electron-accepting．The microstructure of the polymer is determined with 13C-NMR spectroscopy．The polymer has a random distribution of the configurational sequences and head-to-hail regiosequence．It is assumed that the polymerization proceeds via a cationic coordination mechanism．