Temperature-triggered self-separating swelling poly(ionic liquid)s as efficient catalysts for CO2 cycloaddition reactions

Abstract

The cycloaddition reaction of CO₂ is one of the most promising pathways for CO₂ utilization due to its 100% atomic utilization rate and the generation of value-added carbonate products. However, it typically requires organic solvents, high temperatures, and elevated pressures. Swelling poly(ionic liquid)s (SPILs), capable of spontaneously forming porous structures under specific solvent and atmospheric conditions, are potential catalysts but face challenges in efficient catalyst–product separation. In this work, a thermosensitive SPIL catalyst, P-[VC₁₂Im]-C₁₂-Br, exhibiting temperature-responsive swelling behavior in the reaction substrate (epichlorohydrin), was designed and synthesized. When applied to CO₂ cycloaddition under solvent-free and atmospheric conditions at 80 °C, it achieved a 91.07% yield of the target product, chloromethyl oxazolidinone. Upon reaction completion, cooling to 25 °C triggered spontaneous catalyst contraction and separation from the product, enabling successful high-temperature catalysis and low-temperature separation. Moreover, P-[VC₁₂Im]-C₁₂-Br exhibited excellent recyclability (6 cycles) and broad substrate adaptability. The catalyst undergoes hydrogen bond-induced swelling at elevated temperatures, forming porous channels. The exposed active sites (Br⁻) facilitate epoxide ring-opening via nucleophilic attack, while the imidazolium rings assist in CO₂ capture and activation. These components synergistically catalyze the cycloaddition process. This study provides a novel strategy for efficient CO₂ conversion and also offers fundamental insights and practical guidance for developing a controllable SPIL catalyst.