Abstract
Mononuclear and dinuclear salen-co(III) catalysts were designed for carbon dioxide (CO2) and propylene oxide (PO) copolymerization. The dinuclear system maintained its activity with a turn over frequency (TOF) of 406h−1 at [PO]/[Cat]=20,000. In contrast, the mononuclear catalyst system almost lost its activity with a TOF of 3h−1. The two cobalt centers in dinuclear structure may work synergistically due to the conjugated structure. This may contribute to the enhancement of the activity. The dinuclear catalyst system offered the highest molecular weight (Mn=200,000) among reported dinuclear catalysts heretofore. Polymerization mechanism for the dinuclear catalyst system was postulated based on the subtly designed experiments. Synergy effect with the positive help of cocatalyst was explored. To further enhanced the thermal property of poly(propylene carbonate) (PPC), poly(cyclohexene carbonate) (PCHC) was incorporated. The glass transformation temperature of the copolymer of PPC-PCHC could be adjusted by the feed ratio of PO and cyclohexene oxide (CHO).
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