Hydrophobic Ionic Porous Aromatic Frameworks with Hydrogen-Bond-Donor Sites for Cooperative Metal-Free CO ₂ Cycloaddition

Porous aromatic frameworks are robust hydrophobic polymer networks with high surface areas and chemical stability, providing a versatile platform for functionalization. In this work, PAF-30 was postsynthetically modified with quaternary ammonium groups, either alone or combined with hydroxyl functionalities, yielding PAF-30-TEA, PAF-30-DMEA, and PAF-30-MDEA. The polymer framework offers hydrophobic micropores that concentrate CO2 at cation-halide sites, while hydroxyl groups act as hydrogen-bond donors that polarize epoxides, creating cooperative catalytic environments. Catalytic performance was evaluated by solvent-free CO2 cycloaddition to cyclic carbonates (110 °C, 10 bar). PAF-30-DMEA shows an initial activity of 84 h–1 and achieves 84% yield in 6 h at low catalyst loading (ECH/Br = 300), outperforming PAF-30-TEA (51 h–1). Arrhenius analysis indicates apparent activation energies of 55 and 82 kJ·mol–1 for PAF-30-DMEA and PAF-30-TEA, respectively, consistent with hydrogen-bond-assisted epoxide activation within hydrophobic pores. Durability tests reveal a rate-stability trade-off: PAF-30-DMEA is the most active, whereas PAF-30-TEA retains a higher activity across five cycles. These results establish PAF-30 as a polymer-first catalyst platform in which the interplay among framework structure, surface functionalization, and pore architecture governs catalytic performance and potential applications. The hydrophobic pore environment, together with well-defined ionic and hydrogen-bonding motifs, enables metal-, solvent-, and cocatalyst-free CO2 conversion into cyclic carbonates. The derived structure–property–performance relationships define practical design rules for scalable polymer catalysts for carbon capture and utilization.