Ring-Opening Polymerization of Propylene Oxide Catalyzed by a Calcium-Chloride-Modified Zinc-Cobalt Double Metal-Cyanide Complex

Highly active CaCl2-modified Zn-Co(III) DMCs were prepared. XRD results showed that the modified catalyst Ca-DMC containing 0.14 wt.-% CaCl2 was amorphous. A higher polymer yield (>61 kg polymer/g catalyst) and a shorter induction period for ROP of PO were observed for Ca-DMC than for unmodified DMC catalysts. An initiator had an inhibitory effect on the initiation and polymerization rate of PO ROP. As the molar ratio of the initiator functionality to the catalyst was increased, the reaction rate and polymer yield decreased, whereas the induction period increased. An increase in reaction temperature tended to reduce the polymer yield and broaden the MWD. The C-13 NMR spectrum for an oligomer from a model polymerization without an initiator revealed that the main terminal unit of the polymer was -CH2CH(CH3)OH because H2O in the system participated in reaction initiation. Cl- and t-BuOH may also initiate the reaction according to the small amounts of terminal -CH2Cl and -OC(CH3)(3) units observed by C-13 NMR spectroscopy. On the basis of common characteristics and some new evidence for DMC catalysis, a mechanism similar to a classical coordination insertion process is proposed.