Simple preparation of poly(ionic liquids) containing hydrogen bond donors for efficient catalysis of CO2 cycloaddition

Incorporating hydrogen bond donor (HBD) groups into poly(ionic liquids) (PILs) has emerged as an effective strategy to enhance their catalytic performance in the cycloaddition of CO 2 and epoxides. However, developing polymeric catalysts that combine a high density of ionic sites with tunable HBD functionalities remains challenging. Accordingly, this study adopts a synergistic functional design strategy to construct bifunctional PILs catalysts bearing either hydroxyl or carboxyl groups on imidazolium and pyridinium backbones via a facile two-step synthetic route. In the cycloaddition of CO 2 and epoxides, all HBD-functionalized PILs exhibited significantly enhanced catalytic activity. Among them, the carboxyl-functionalized imidazolium-based PIL (PIMIBr-COOH) demonstrated the highest performance, affording a 95 % yield of chloropropylene carbonate (CPC) under relatively mild conditions (90 °C, 4 h, 0.5 MPa CO 2 ). In addition, PIMIBr-COOH exhibited excellent recyclability and broad substrate scope. Density functional theory (DFT) calculations revealed that the HBD groups effectively activate epoxide substrates. In situ FT-IR spectroscopy further revealed the critical nucleophilic role of bromide ions (Br - ) in facilitating the epoxide ring-opening process. Based on these findings, a plausible reaction mechanism was proposed for the PIMIBr-COOH catalyzed cycloaddition of CO 2 and epoxides, involving epoxide activation, nucleophilic ring opening, and cyclic carbonate formation through the synergistic interaction between the carboxyl group and Br - . This work not only elucidates the catalytic mechanism but also provides theoretical guidance for the functional design of ionic polymer catalysts toward efficient and sustainable CO 2 valorization.