Construction Of Functional Porous Organic Polymers Via A Bottom-up Strategy For CO₂ Capture And Conversion To Cyclic Carbonates

As the main greenhouse gas,excessive emission of CO₂ will lead to climate change and various environmental problems.For this reason,our country has stated that it will strive to achieve the long-term goal of peaking carbon emissions by 2030 and achieving carbon neutrality by 2060.CO₂ capture and utilization is currently recognized as an effective way to reduce carbon emissions and achieve carbon neutrality.CO₂ can be converted into various high-value fine chemicals such as carbonates,urea derivatives,carbamates,carboxylic acids,Alkanes and alcohols,etc.Among them,the cycloaddition reaction of CO₂ and epoxide to generate cyclic carbonate has 100%atom economy,which is one of the greenest and most environmentally methods.Moreover,the obtained cyclic carbonate has high boiling point and flash point,low toxicity,biodegradability and high solubility,so that it widely used in polar solvents,industrial lubricants,lithium-ion battery electrolytes and polycarbonate.A variety of homogeneous and heterogeneous catalytic materials such as metal complexes,organohalide homogeneous catalysts,metal-organic frameworks,and porous organic polymers have been developed for catalytic conversion of CO₂ to cyclic carbonates.Among them,porous organic polymers are widely used in this field due to their many advantages,such as good physical and chemical stability,high specific surface area,and high CO₂ adsorption.Therefore,we used a bottom-up strategy to design a series of functional porous organic polymers for catalytic conversion of CO₂ and epoxide cycloaddition reactions.The main research contents are as follows:（1）Aiming at the complex preparation process of metalloporphyrin-based porous organic polymers,it is difficult to modify and construct functionalized frameworks.An Alder-Longo strategy was used to synthesize a metalloporphyrin-based ionic polymer Zn Por-CP.The synthetic method has the characteristics of simple operation process and without need to synthesize porphyrin rings in advance.Zn Por-CP catalyst has high catalytic activity,it can catalyze the reaction of CO₂ and epoxides under mild conditions（100°C,1 MPa）,and exhibits high catalytic activity and stability,as well as easy to recycle.This is because the catalytic material possesses both a Lewis acid zinc center and a nucleophilic bromide ion,and the synergistic catalysis between the two is very beneficial for the ring-opening of epoxides.（2）In view of the low specific surface area of the prepared metalloporphyrin-based catalysts,we further prepared a series of metalloporphyrin-based porous ionic polymers MPor-PIPs.This type of catalyst has the characteristics of easily accessible catalytic active sites,high specific surface area(761cm~2·g^-1),great CO₂ adsorption(2.1mmol·g^-1)and high selectivity.It is found that Al Por-PIP-Br exhibits high catalytic activity,which can achieve the catalytic conversion of CO₂ to prepare cyclic carbonates at room temperature and pressure.This is mainly attributed to the strong Lewis acidity of the polymer and the enhanced synergistic effect of the two active sites.（3）In view of the low cation loading of porphyrin macrocycle（such as K⁺,Na⁺,Hg⁺）,We conceived the preparation of polymers with flexible macrocycles by the same strategy.Using amino-functional crown ethers as raw materials,a series of crown ether-based organic polymers CE-POPs were synthesized by Schiff base condensation reaction.Since the polymer has the advantage of being easily complexed with potassium ions,it can achieve high catalytic activity for catalyzing the reaction of CO₂ and epoxides to cyclic carbonates.Studies have shown that the specific introduction of phenolic hydroxyl groups into the polymer backbone can significantly improve its catalytic performance due to the increased dual activation mode of hydrogen bond donors for epoxides.