Study On The Kenitics And Catalytic Reaction Of Carbon Dioxide And Epoxides

The chemistry of CO₂ has received much attention in decades from both environmental and economical points of view:reduction of greenhouse gas and utilization of the least-expensive C1-feedstock.The syntheses of cyclic carbonates and polycarbonates are technologically viable processes of CO₂ fixation by coupling CO₂ and epoxides.Both cyclic and polymeric products have important industrial applications.Cyclic carbonates are an important class of compounds that can be used as polar aprotic solvents and degreaser,as electrolytes in lithium ion batteries,and as synthetic intermediates.On the other hand,polycarbonates have been proposed as one of the most useful engineering plastics,including packaging and elastomers.This thesis focuses on the catalytic reaction of carbon dioxide with epoxidesand isdivided in the following six chapters.Chapter 1:The synthesis and application of polycarbonates and cyclic carbonates are systematically reviewed.The perspective and progress of the catalytic reaction between CO₂ and epoxides is detailed demonstrated.Chapter 2:A series of quaternary onium modulated SalenCoXY catalysts incorporating the N,N'-bis?salicylidene?ethylene diaminato?Salen?ligand and quaternary onium units were designed and synthesized.Chapter 3:These bifunctional SalenCoXY catalysts were applied to the copolymerization of CO₂ and propylene oxide.The impact factors of the axial anion X,the counter anion Y and the property of quaternary onium group evidently affected PPC selectivity and degree of polymerization.Based on the study of macrokinetics,a competing reaction mechanism between the formation of PPC and CPC was proposed.The apparent activation energy of each formation was obtained.Chapter 4:The effect of catalyst concentration on the reaction rate was investigated.It indicates that the copolymerization of carbon dioxide and propylene oxide is a second order reaction of catalyst.The result confirms that PPC is generated through a bimetallic transition state resulting in lower barrier.Chapter 5:To improve the property of polymer,we devised and synthesized a novel biodegradable cross-linked polycarbonate.The primary polymer is obtained by quaternary copolymerization of carbon dioxide,propylene oxide,TBS-protected glycidyl ether and allyl glycidyl ether.After deprotection of TBS group,the brush polymer is synthesized through ring-opening polymerization?ROP?of lactide.Then,BPO initiates secondary crosslinking polymerization giving the target polymer.The physical and mechanical properties were preliminarily tested.Chapter 6:We developed a novel binary catalyst system of Pd/C and Lewis base to catalyze the cycloaddition of carbon dioxide to epoxides.The effects of cocatalyst,CO₂ pressure,reaction temperature and time were investigated systematically.Pd/C as a heterogeneous catalyst could be recycled 5 times and retained high catalytic activity and selectivity.