Mechanistic insight into initiation and chain transfer reaction of CO2/cyclohexene oxide copolymerization catalyzed by zinc-cobalt double metal cyanide complex catalysts

Although zinc?cobalt (III) double metal cyanide complex (Zn?Co (III) DMCC) catalyst is a highly active and selective catalyst for carbon dioxide (CO2)/cyclohexene oxide (CHO) copolymerization, the structure of the resultant copolymer is poorly understood and the catalytic mechanism is still unclear. Combining the results of kinetic study and electrospray ionization-mass spectrometry (ESI-MS) spectra for CO2/CHO copolymerization catalyzed by Zn?Co (III) DMCC catalyst, we disclosed that (1) the short ether units were mainly generated at the early stage of the copolymerization, and were hence in the head of the copolymer and (2) all resultant PCHCs presented two end hydroxyl (?OH) groups. One end ?OH group came from the initiation of zinc?hydroxide (Zn?OH) bond and the other end ?OH group was produced by the chain transfer reaction of propagating chain to H2O (or free copolymer). Adding t-BuOH (CHO: t-BuOH = 2:1, v/v) to the reaction system led to the production of fully alternating PCHCs and new active site of Zn?Ot-Bu, which was proved by the observation of PCHCs with one end ?Ot-Bu (and ?OCOOt-Bu) group from ESI-MS and 13C NMR spectra. Moreover, Zn-OH bond in Zn?Co (III) DMCC catalyst was also characterized by the combined results from FT-IR, TGA and elemental analysis. This work provided new evidences that CO2/CHO copolymerization was initiated by metal?OH bond. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012