Bowtie-Shaped Bio-Based Zwitterionic Polymer-Catalyzed Chemical Fixation of Carbon Dioxide

Developing green and low-cost catalytic systems is highly desired in the chemical conversion of carbon dioxide into value-added products. A zwitterionic polymer, with a bowknot-like morphology consisting of uniform nanosheets, is synthesized from biomass-derived cinnamic acid via a simple copolymerization strategy. The as-prepared zwitterionic polymer (PEMP) has been employed to catalyze the cycloaddition reaction of epoxides and atmospheric CO2, affording 9 cyclic carbonates with good to excellent yields under metal-free/solvent-free/cocatalyst-free conditions. PEMP with outstanding stability can be reused 5 times at least without an obvious loss of catalytic activity. The reaction mechanism was elaborately investigated by in situ Fourier transform infrared spectra tests, control experiments, and density functional theory calculations, demonstrating that the catalytic cycloaddition of CO2 and epoxides over PEMP occurs through the preactivation of epichlorohydrin. Moreover, it is illustrated that the synergistic effect between the carbonate anion and quaternary ammonium cation on the zwitterionic polymer played a crucial role in promoting the activation of epoxides and CO2.