Hydroxylamine-Anchored Covalent Aromatic Polymer for CO2 Adsorption and Fixation into Cyclic Carbonates

Hydroxylamine-anchored covalent aromatic polymer (CAP-DAP) was synthesized from p-terphenyl and 1,3,5-benzene tricarbonyl chloride, followed by subsequent functionalization with 1,3-diamino-2-propanol for CO2 capture and metal free catalysis in CO2-epoxide cycloaddition reactions. The novel CAP-DAP material was characterized using various analytical techniques. It showed very good CO2 adsorption capacity of 153 mg/g along with a high (CO2/N-2) selectivity of 86 at 273 K/1 bar, in contrast to bare CAP, which exhibited moderate CO2 adsorption of 136 mg/g with a CO2/N-2 selectivity of 47. CAP-DAP also displayed high catalytic activity for CO2-epoxide cycloaddition reactions under mild and solvent-free conditions. The synergistic effect between metal-free CAP-DAP and tetrabutylammonium bromide (n-Bu4NBr) enabled a high epoxide conversion of 98% coupled with an excellent product selectivity of 99% at 60 degrees C, 1 bar CO2, and a reaction time of 12 h. Faster reaction kinetics with reaction times <6 h was possible at 80 degrees C. The catalyst also showed excellent reusability and no leaching of active species was observed from the spent catalyst. Based on experimental results, a plausible reaction mechanism for CO2-epoxide cycloaddition reaction over CAP-DAP catalyst has been proposed.