Poly(ionic liquid)s with unique adsorption-swelling ability toward epoxides for efficient atmospheric CO2 conversion under cocatalyst-/metal-/solvent-free conditions

Abstract

Developing a simple and efficient heterogeneous catalyst for the cycloaddition of epoxides with CO₂ under atmospheric pressure and cocatalyst-/metal-/solvent-free conditions remains a great challenge. Herein, poly(ionic liquid)s (P-[VRIm]Br-crosslinker-x) with unique adsorption-swelling ability toward epoxides are designed and facilely synthesized via free radical polymerization in water. The adsorption-swelling of epoxides by P-[VRIm]Br-crosslinker-x is controllable, reversible, and widespread, resulting from the strong interactions between the poly(ionic liquid)s and epoxide molecules, especially the hydrogen-bonding interaction. Superior CO₂ cycloaddition is realized in the P-[VRIm]Br-crosslinker-x catalyst through the adsorption-swelling effect. Specifically, P-[VC6Im]Br-C8-5% with 54.1 mmol g⁻¹ adsorption-swelling ability toward styrene oxide achieves 89.3% yield and >99% selectivity in the cycloaddition of styrene oxide with CO₂ to styrene carbonate under mild conditions (1 atm, 80 °C) without cocatalyst/metal/solvent consumption. Moreover, P-[VC6Im]Br-C8-5% can be easily recovered by deswelling, and shows good reusability and stability after five cycles for a total of 180 h. The adsorption-swelling property of P-[VRIm]Br-crosslinker-x to epoxides not only prompts the active centers to be fully exposed to the reactants but also induces the enrichment of epoxides during the whole catalytic process, thus accelerating the CO₂ cycloaddition reaction rate. This work furnishes new insights for improving the activity of CO₂ cycloaddition and would guide the design of efficient poly(ionic liquid) catalysts for atmospheric CO₂ conversion.