The embedding of 1,8-diazabicyclo[5.4.0]undec-7-ene into hyper-crosslinked ionic polymers for efficient CO₂ conversion at atmospheric pressure

The preparation of cyclic carbonates via CO₂ cycloaddition reaction was crucial for the lithium industry. Herein, a series of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) based hyper-crosslinked ionic polymers with different ionic site densities were prepared by simultaneously Friedel-Crafts alkylation and quaternization reactions. The obtained P[DBU]DCX(1:1) with a high ionic site density (1.45 mmol‧g⁻¹), prepared by the equimolar ratio of 1,8-diazabicyclo[5.4.0]undec-7-ene and α,α′-dichloro-p-xylene, exhibiting excellent catalytic performance with a chloropropylene carbonate (CPC) yield of 98.8 % and selectivity of 99.3 % at atmospheric pressure. Meanwhile, the conversion capacity was comparable with other catalysts. Moreover, the CO₂ cycloaddition reaction over P[DBU]DCX(1:1) catalyst followed pseudo-first-order kinetics, and the activation energy (Ea) was obtained to be 28.7 kJ/mol by performing kinetic experiments at different temperatures. In addition, it also had a good reusability and universality for different epoxides. The synergistic effects of abundant quaternary nitrogen cations derived from DBU and chlorine anions on the activation of CO₂ and epoxide were explored based on density functional theory calculation. This study offers a new approach for the design and application of hyper-crosslinked ionic polymers for efficient CO₂ conversion at atmospheric pressure.