Two series of flexible ketone-bridged nanoporous organic polymers (NOPs) are readily prepared through one-pot Friedel-Crafts acylation polymerization using pyromellitic dianhydride (PMDA) and terephthaloyl chloride (TC) as acylation reagents, respectively. The carboxyl-appended samples (termed NOP-52@COOH and NOP-53@COOH), derived from PMDA, feature a stable spherical morphology. Unexpectedly, our NOP-52@COOH and NOP-53@COOH deliver much higher surface areas (eg. 738 m(2) g(-1) for NOP-52@COOH) and pore volumes (eg. 0.53 cm(3) g(-1) for NOP-52@COOH) than the carboxyl-free samples (i.e. NOP-52 and NOP-53). This is significantly different from the reported trend that the introduction of appended group always leads to inferior surface area and pore volume. The enhancement in porosity originates from the hydrogen-bonding effect between carboxyl and the ketone linkage that effectively prevents the networks from collapsing. More importantly, the as-made carboxyl group-containing networks exhibit stronger affinity towards guest CO2 molecules after comparing to those carboxyl-free ones, and have a competitive CO2 capture capacity under ambient conditions (159 mg g(-1), 273 K/1 bar). This provides a feasible pathway for both developing high-surface-area organic polymers with flexible linkages and engineering pore surface properties.