Alternating copolymerization of carbon dioxide and cyclohexene oxide catalyzed by silicon dioxide/Zn-CoIII double metal cyanide complex hybrid catalysts with a nanolamellar structure

Air-stable hybrid catalysts of silicon dioxide/double metal cyanide complexes (Si-DMCCs) based on Zn-3[Co(CN)(6)](2) (ZHCC) were prepared by an in situ Sol-gel method. The Si-DMCCs showed low crystallinity and a nanolamellar structure with a thickness of similar to 40-60 nm. In particular, a lamellar structure of regular hexagonal shape was observed for Si-DMCCs with low SiO2 content. These catalysts had very high catalytic activity for alternating copolymerization of cyclohexene oxide (CHO) and carbon dioxide. A turnover number of 11,444, turnover frequency of 3815 h(-1), and apparent efficiency of 7.5 kg polymer/g ZHCC (similar to 24.0 kg polymer/g Zn) were achieved at 3.8 MPa and 100 degrees C. The poly(cyclohexenylene carbonate) (PCHC) polymers obtained were completely atactic with a molecular weight (Mn) of similar to 10 kg/mol and polydispersity of 2.0-3.0. The PCHCs had a structure of nearly alternating CHO and CO2 units, with a molar fraction of carbonate units of 0.44-0.47. Preliminary investigations of the mechanism suggest that nucleophilic attack by neighboring oxygen atoms is involved in copolymerization initiation with Zn-Co-III DMCCs. (C) 2008 Wiley Periodicals, Inc.