A series of porous organic polymers (POPs) with tunable nitrogen functionality and hierarchical porosity were successfully synthesized from the one-step copolymerization of divinylbenzene with 4-vinylpyridine or 1-vinylimidazolate under solvothermal conditions. The FTIR results, XPS spectra, and elemental analysis validated the incorporation of different kinds and contents of nitrogen species into the framework-synthesized POPs. The N₂ adsorption isotherms at −196 °C and SEM and TEM images revealed that the synthesized POPs have large surface areas and abundant meso–macropores. The CO₂ and N₂ adsorption experiments demonstrated that the synthesized POPs have competitive capacity for CO₂ at a relatively low pressure of 0.15 bar (0.64–1.47 mmol g⁻¹ at 0 °C and 0.49–0.87 mmol g⁻¹ at 25 °C) and exceptionally high IAST selectivity for CO₂/N₂ (0.15/0.85) at 1 bar (74.9–154.8 at 0 °C and 91.8–224.5 at 25 °C). The CO₂/N₂ selectivity is superior to that of most other reported physical adsorbents. This work provides a facile approach to the targeted synthesis of nitrogen-functionalized POPs with potential applications in the selective capture of CO₂ from flue gas.