Facile One-Step Synthesis of Hyper-Cross-Linked Ionic Polymers with High Ionic Content for Efficient CO ₂ Conversion

The primary challenge in the one-step synthesis of hyper-cross-linked ionic polymers (HIPs) for catalyzing CO2 cycloaddition reactions lies in their relatively low ionic content. In this study, we successfully synthesized a series of HIPs from different imidazole compounds and cross-linkers and systematically regulated their textural properties. It was found that HIPs derived from 1-benzylimidazole (BnIm) possessed higher nitrogen and ionic contents than those synthesized from other imidazole monomers; the conclusion was further confirmed by density functional theory (DFT) calculations based on molecular electrostatic potential (MESP) and Mulliken charge distributions. Owing to its high nitrogen (3.72 wt %) and ionic content (1.33 mmol g–1), [HBnIm-DCX-1]Cl exhibited outstanding catalytic activity, affording a 99% yield in the CO2/styrene oxide cycloaddition at atmospheric pressure within 4 h and maintaining SC yields above 90% even at moderate reaction temperatures. Additionally, extensive catalytic evaluations confirmed its broad substrate scope and excellent recyclability. This study elucidates the role of benzene rings and their Friedel–Crafts alkylation in modulating the quaternization of imidazole nitrogen atoms. Based on this insight, we established a facile one-step method to prepare HIPs with high ionic content and demonstrated the decisive role of this content in CO2 cycloaddition catalysis.