Copolymerization Of Carbon Dioxide And Propylene Oxide Over Double Metal Cyanide Catalyst Prepared By Microemulsion Method For The Synthesis Of Polypropylene Carbonate Polyols

As the main greenhouse gas and a renewable resource, CO2gets more and more attention with the globle dwindling of oil resources and climate warming. Copolymerization of CO2and propylene oxide to synthetize biodegradable polypropylene carbonate (PPC) and its corresponding polyols have become one of the most important ways of carbon dioxide utilization. Double metal cyanide (DMC) catalyst is one of the main catalysts for copolymerization of CO2and propylene oxide, which is usually prepared by precipitation method. In this work, a new DMC catalyst preparation method-reverse microemulsion method was developed in order to further improve the catalyst structure, morphology and catalytic performance. The two catalysts were compared by elemental analysis, ICP-AES, XRD, SEM, and BET methods. The results showed that the Zn3[Co(CN)6]2crystallinity of the catalyst by microemulsion method was obviously decreased with the incorporation of more ZnCl2, tert-butyl alcohol and H2O than that of the catalyst prepared by traditional precipitation method. The amount of catalyst obtained by the new method was increased by72%. The catalyst prepared by microemulsion method has much more meso-and macro-pores despite of lower surface area, which might benefit for the mass transfer in the subsequent polymerization reaction. It was confirmed that the catalyst prepared by microemulsion method exhibited much higher activity of copolymerization of CO2and propylene oxide than that of by solution precipitation method.PPG400was used as a chain transfer agent in the copolymerization of CO2and propylene oxide to synthetize polypropylene carbonate polyols over DMC catalyst prepared by microemulsion method. The results showed that the molecular weight of polymer can be regulated from2000-10000through changing the dosage of PPG400with the CO2incorporation from3to35%. But the addition of PPG400will decrease the catalyst activity. When the molecular weight of PPG increased, the initiation time of copolymerization was reduced and the polymer showed more high molecular weight portion. The activity of catalyst was improved when reaction temperature was increased, but it would decrease selectivity of catalyst. When reaction pressure was increased, the activity and selectivity were both increased. The highest activity can be up to5611g polymer/g catalyst when17.6g PPG400/50mg catalyst was used. The successful synthesis of polypropylene carbonate polyols was confirmed by hydroxyl value measurement of products. A coorelation between the molecular weight of polymer and the selectivity of the catalyst was also found.