POSS-based polyionic liquids for efficient CO2 cycloaddition reactions under solvent- and cocatalyst-free conditions at ambient pressure

Abstract

The conversion of CO₂ into value-added chemicals has become an imminent research topic and the cycloaddition of CO₂ with a C1 resource to produce cyclic carbonates is a promising pathway for CO₂ utilization. Herein, a series of POSS-based polyionic liquids (PILs) were synthesized by the copolymerization of octavinyl polyhedral oligomeric silsesquioxane (POSS) with an imidazolium ion linker. The prepared PILs have the characteristics of hydrogen bond donors, halogen atom sites, stable pore structures, and thermal stability, and are used as heterogeneous catalysts for the cycloaddition of epoxides with carbon dioxide. The effect of linkers on the cycloaddition is investigated by tuning the ratio of POSS units to imidazolium ions. Under the optimized conditions, the conversion of epichlorohydrin can reach 99.18% at atmospheric pressure with neither co-catalysts nor solvents. It is concluded that the reaction of the cycloaddition of epoxides with carbon dioxide follows pseudo-first-order kinetics. Moreover, the presence of the catalysis of PILs leads to a significant decrease in the activation energy barrier for cycloaddition. The catalyst can be facilely recovered due to its high stability, and only a slight decrease in conversion was observed after five successive runs. In addition, the mechanism of PILs catalyzing the cycloaddition reaction of epoxides with CO₂ is proposed. This work not only provides a sustainable and green process for CO₂ cycloaddition, but also highlights the potential of using PILs for CO₂ utilization.