Ring-opening Polymerization Of Propylene Oxide Catalyzed By Double Metal Complex In Microchannel Reactor

Polyether polyol is synthesized usually by the ring-opening polymerization of epoxides and can be used for polyurethane,widely applied in furniture,construction,automobile,aerospace and medicine etc.Among the catalyst used for ring-opening polymerization of epoxides,double metal complex(DMC)is usually preferred in industry considering molecular weight,molecular weight distribution(MWD),unsaturation,efficiency,etc.However,the rate of the ring-opening polymerization of epoxides catalyzed by DMC is extremely fast and the polymerization enthalpy of epoxides is large,resulting in large heat load during the whole reaction process.In this case,the problem of safety is serious.Semi-continuous "starvation polymerization"method have to be adopted in industry,which is extremely inefficient.The heat exchange process is greatly enhanced in the microchannel reactor(MCR)because of its large surface area to volume ratio and the safety problem can be avoided to some extent because of its small reaction space.As a result,MCR is especially suitable for dangerous reactions with extremely fast exothermic rate.MWD can influence the properties of obtained materials.Therefore,it's of great importance to investigate how to obtain polyether polyol quickly and safely in the reactor and how to control the MWD.In this work,the ring-opening polymerization of propylene oxide(PO)catalyzed by DMC was carried out in the MCR and the main conclusions can be summarized into five points:1.The induction period still existed in the ring-opening polymerization of PO catalyzed by DMC.The induction period can be shortened by increasing the reaction temperature in a proper range.In addition,increasing the pressure of the reaction system through extending the MCR's length,or increasing the concentration of active centers by reducing the ratio of PO to initiator can promote coordination of PO to the vacancies around Zn atom in DMC,thereby shortening the induction period.What's more,the result analysis of 1H NMR indicated that the epoxy of PO was opened after PO being coordinated to the vacancies around Zn atom.2.The monomer conversion at the outlet of the MCR usually reached 100%within 2 minutes of average residence time,and the continuous and efficient synthesis of polypropylene glycol(PPG)is safely realized.Additionally,the molecular weight of the obtained PPG has a good linear relationship with monomer conversion,that is,the ring-opening polymerization of PO catalyzed by DMC has characteristic of living,but this characteristic originated from the chain transfer reaction.Compared with the chain propagation reaction,the greater the degree of chain transfer,the more obvious the characteristic of living polymerization and the narrower the MWD.3.On the basis of polymerization mechanism,a MWD model was established and an explicit expression of polydispersity index(D)was obtained.The simulation results showed that possible lack of chain transfer or the insufficient chain transfer will cause larger D,namely broad MWD.4.With the aid of the y-type parallel tanks-in-series model,the mixing characteristics of the polymer fluid in the MCR were fully investigated.It was found that increasing the MCR's length,decreasing the fluid viscosity or increasing the flow rate when the residence time is relatively sufficient,can increase the ratio of convection to axial dispersion,improve the degree of radial micromixing,and narrow the residence time distribution.5.The influence of operating conditions such as reaction temperature,flow rate of fluid,reactant ratio,etc.on MWD was studied,and the change law of MWD was revealed from the point of polymerization mechanism and mixing characteristics.In addition,the MWD of PPG was significantly reduced by reducing the spiral diameter of MCR.Based on fully understanding the mechanism of ring-opening polymerization of PO catalyzed by DMC and the mixing characteristics of polymer fluid in the MCR,the optimization of MWD is realized,which can provide important scientific basis for the continuous,rapid and safe synthesis of PPG in the MCR and the regulation of MWD.