Study On The Copolymerization Of Sulfur Dioxide And Epoxy Compounds Catalyzed By Quaternary Ammonium Salt Ionic Liquids And Its Mechanis

In recent years,with frequent respiratory problems,acid rain and a series of environmental problems increasingly prominent,the long-term low utilization rate of sulfur dioxide leads to high environmental pollution.Due to its excellent performance and high added value,sulfur-containing polymeric materials have broad development prospects in many fields.Moreover,the conditions for the synthesis of SO 2 are mild and the products generated will not cause secondary pollution to the environment.Therefore,it has become the most effective green economic approach for the utilization of SO2 resources second to none.Although researchers have developed a variety of catalysts to solve the limited problem of SO 2 copolymerization,most of them have shortcomings such as harsh reaction conditions,difficult product separation and recovery,and limited industrial application in the catalytic process.Ionic liquids（ILs）are usually used as nucleophiles,whose anionic electrons provide charge to realize remote effect and lead to free radical polymerization,so as to realize chain growth.Therefore,ILs is often used in the ring-opening reaction of epoxy compounds.Tetrabylammonium bromide（TBAB）is mostly used as catalyst or cocatalyst,and is an outstanding representative of quaternary ammonium salts ILs.Based on this,TBAB is used as catalyst in this paper to directly catalyze the copolymerization of SO 2 and CHO.The optimal conditions of TBAB catalyzed copolymerization were as follows:50℃,6 h,TBAB/CHO=1:500（the a mount of CHO was 10 m L）.Under the optimal conditions,the structure of the polymer was determined by ¹H NMR,FT-IR and other characterization meth ods,and the analysis results were as follows:The content of sulfite unit,the selectivity of PCS and the co nversion of CHO monomer were 87.72%,90.10%and 98.50%,respectively.The TON value was 492.48,the average molecular weight was 4.66×10³ g·mol^-1,and the PDI value was 1.43.With the optimal catalytic conditions as the experimental research background,co ntinue to explore the influence of different negative and cations on copolymerization in ILs.The selection of catalysts takes TBAB as the core,the selection of different anionic catalysts starts from tetrabylhalide,and the anionic ions of different cati onic catalysts are all nucleophiles of bromine ions.Ionic liquids have been widely used as catalysts in copolymerization systems.There is no significant difference in the catalytic effect between different cationic catalysts and different halide anions.Halide anions play a leading role in the ring-opening of epoxides,and catalysts containing bromide ions have the best catalytic effect.In addition,TBAB also has a good catalytic effect for the copolymerization of other epoxides and SO 2.The thermal degradation of PCS of SO2 and CHO copolymerized products catalyzed by TBAB was analyzed by Flynn-Wall-Ozawa（FWO）,Kissinger and Coats-Redfern methods.The average activation energy of FWO method is 134.88 k J·mol^-1,and the linear regression coefficient is 0.9 9235.The average activation energy of Kissinger method is 105.41 k J·mol^-1,and the linear regression coefficient is 0.98858.In contrast,FWO method has better linear fitting data and is more suitable for the study of thermal degradation kinetics of this system.The Coats-Redferns method showed that the A2 mechanism of the nucleation and growth model（Avrami equation（1））was the most probable mechanism of the thermal degradation kinetics of TBAB catalyzed copolymerization.Its function expression was g（α）=[-ln（1-α）]^1/2,and the activation energy calculated by this function was:114.66 k J·mol^-1.Finally,density functional theory（DFT）was used to optimize the overall geometric structure of tetrabylhalide catalyst and substrate to obtain the best quantum mechanical structure.On this basis,the simulation calculation of CHO ring-opening in the copolymerization of SO2 and CHO catalyzed by different halide anions was carried out.The transition state（intermediate）of CHO ring-opening process in tetrabylhalide catalyzed copolymerization is obtained.The required energy barrier of halogen anion when CHO ring-opening generates transition state intermediate is as follows:The Gibbs free energy required for ring-opening of F^->Cl^->I^->Br^-.Among them,Br^-Gibbs free energy required for ring opening is the lowest,and the reaction is relatively eas y to occur.Combined with the thermal degradation kinetics study in Chapter 4 of this paper,the mechanism of the copolymerization of SO 2 and epoxide catalyzed by tetrabylhalide was predicted.