The efficient metal- and halogen-free polymer catalyst for the intensification on CO2 cycloaddition

An environmentally friendly polymer catalyst (PAS) was synthesized via inverse emulsion polymerization using acrylic acid (AA) and 1-vinyl imidazole (VI) as monomers. The excellent catalytic activity of PAS was attributed to the synergistic effects of the carboxyl groups (-COOH) as hydrogen bond donors and N-heterocyclic carbene (NHCs) as electron donor, as well as the swelling properties of the polymer, which can enrich the substrate into the polymer network, increasing the contact between the substrate and active sites. Characterization results from thermogravimetric (TG) analysis and small-angle X-ray scattering (SAXS) showed that the excessive imidazole addition disrupted the polymer's chain-like structure, significantly reducing its swelling properties. And, the catalytic performance is influenced by both the amount of imidazole in PAS and the swelling properties of the polymer. Finally, the reaction mechanism of the CO₂ cycloaddition reaction catalyzed by PAS was proposed and validated through density functional theory (DFT) calculations.