Rational design concepts were used to prepare a novel porous benzimidazole-linked polymer (BILP-101) in a simple one-pot reaction. BILP-101 has exhibited ultra-microporosity (0.54 nm), very high CO2 uptake (∼1 mmol g(-1), 4 wt%, 0.15 bar/298 K) and exceptional CO2/N2 selectivity of 80 (298 K), which results in remarkable working capacity and regenerability for CO2 capture applications.