Study On The Regulation Of CO₂-epoxides Reaction

CO₂ is a main greenhouse gas.It is also a cheap,non-toxic,abundant and renewable C1 feedstock.Owing to envirormental and energy concerns,utilization of CO₂ has received more and more attention in recent years.One of the most promising routes is the reaction of CO₂ with epoxide to synthesize cyclic carbonates or aliphatic polycarbonate.At present,the research about this work mainly concentrates on two aspects.The first is to develop a cheap and highly efficient catalytic system to obtain one of the products with high selectivity under mild conditions.Secondly,poly（propylene carbonate）（PPC）is prepared by alternating copolymerization of CO₂ and propylene oxide（PO）.However,it has poor thermal and low mechanical properties.Thus,the other important research direction is to modify the PPC to improve its overall performance and realize its large-scale utilization.Based on the facts,the main studies in this thesis are as follows:1.It was for the first time demonstrated that succinimide（SI）-KI is an efficient catalyst system to synthesize propylene carbonate（PC）from CO₂ and PO.A synergistic effect was observed between SI and KI.It enables the cycloaddition reaction to take place under solvent-free mild conditions（70°C and 0.4MPa）for only 4 hours,with a PC yield as high as 97.5%.SI-KI is suitable for the cycloaddition reaction of CO₂ with other epoxides.The overall condition is milder than the reaction catalyzed by the other KI involved co-catalyst systems reported in literatures.Kinetic studies show that the reaction has a reaction order of 1 for both SI and KI.And compared with using KI alone,the presence of SI-KI can reduce the activation energy of the reaction from 43 kJ·mol^-11 to 22.7 kJ·mol^-1.A reaction mechanism was proposed based on a reaction kinetics study.2.As a new member of nanocarbon-based materials,detonation nanodiamond（DND）,fabricated through carbon-based explosive detonation was for the first time demonstrated to efficiently catalyse the cycloaddition of CO₂ with PO to form PC in the presence of halides（KCl,KBr,KI,TBAI and[BMIm]I）.Among them,DND-KI shows the highest efficiency under mild reaction conditions（0.8 MPa,90°C）and the yield can reach up to 96.4%after 6 h.The excellent catalytic performance stemmed from the synergetic effect between DND and KI.And DND-KI is also applicable to cycloaddition of CO₂ with other epoxides.Furthermore,the catalyst system has good thermal stability and no significant loss was found after ten-cycle utilization.Reaction kinetics studies show that the activation energy of cycloaddition reaction of CO₂-PO catalyzed by DND-KI is 11.1 kJ·mol^-11 lower than that of KI alone.Based on the research results,a possible reaction mechanism was proposed.This work provides a new catalyst for the conversion of CO₂ to cyclic carbonates and opens up new applications for DND.3.The ternary copolymerization of CO₂,PO and cyclohexanedicarboxylic anhydride（CH）was studied using zinc glutarate（ZnGA）as catalyst to improve the overall performance of PPC.The results show that the introduction of CH not only increases the molecular weight of the polymer and the catalytic activity of ZnGA,but also improves the thermal and mechanical properties of PPC.However,the addition of too much CH causes a decrease in polymer yield.When the amount of CCH is 2 mol%relative to PO,the glass transition temperature and maximum thermal decomposition temperature of the obtained terpolymer are 4.4°C and 19°C higher than pure PPC,respectively.The tensile strength is about twice than that of pure PPC.The Young’s modulus is more pronounced,which is 3 times than that of pure PPC.In addition,it is found that the stereoisomerism of CH has little effect on the structure and properties of the terpolymer.