科研之友
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摘要
This review focuses on the recent advances in double metal cyanide complex (DMCC) catalyst and its catalysis for epoxides-involved polymerizations. DMCC is an inorganic coordinated polymer with three-dimensional network, in which the inner metal M-II is linked with the external metal M-I by several cyano-bridges (M-II-C N-M-I, generally, M-I = divalent metal ions such as Zn2+, Fe2+, Co2+, Ni2+, et al., M-II = transition metal ions such as Fe2+, Fe3+, Co2+, Co2+, Ni2+, et al). The external metal M-I on the surface of the catalyst is generally considered to be the active site for the polymerizations due to its unsaturated coordinated structure. DMCC catalyst was initially applied to the catalysis of the ring-opening polymerization (ROP) of epoxides, and then modified and used as a highly active catalyst for making polyether-polyols with both moderate or high molecular weights and low unsaturation degrees. Later, this catalyst was utilized to catalyze the alternating copolymerization of epoxides and CO2 for producing aliphatic polycarbonates. The productivity of DMCC-catalyzed epoxides/CO2 copolymerization is clearly higher than those of other heterogeneous catalysts, while the polycarbonate selectivity of this catalyst is unsatisfied, e. g. : for propylene oxide (PO)/CO2 copolymerization, the maximum alternating degree of the resultant copolymer was up to similar to 74%. That is, the copolymer is a poly (ether-carbonate) with random chain structure. However, Zn-Co-III DMCC exhibits high activity (TOF: 3 815h(-1)) for cyclohexene oxide (CHO)/CO2 copolymerization with high alternating degree of >90%. Furthermore, this catalyst can also be applied to catalyze epoxide/cyclic anhydrides for producing polyesters, epoxide/CS2 copolymerization for producing polythiocarbonates, as well as epoxide/cyclic anhydride/CO2 terpolymerization for producing poly (carbonate-ester) s with high productivity. Based on the research work of our group in recent ten years, this review will discuss the possible structure of the active sites of DMCC and related catalytic mechanism, as well as some common problems for DMCC and DMCC catalyzed polymerizations and possible solutions.
