Poly(ionic liquids (PILs) have received great attention recently for their potential applications in gas capture. In this work, a quaternization reaction and radical polymerization were applied to the synthesis of a quaternary ammonium-based PIL which was further characterized for its structure and properties. Interestingly, although X-ray diffraction showed an amorphous structure, differential scanning calorimetry evidenced that the PIL prepared by freeze-drying possessed low crystallinity compared to PILs prepared by other drying methods, which contributed to its high CO2 absorption (236 mg/g) and good CO2/CO selectivity (6.0) at 303.0 K and 5.0 MPa. To the best of our knowledge, this is the first CO2/CO selectivity observed for PIL material. An absorption-desorption process by the PIL for CO2 separation from syngas at 303.0 K and 5.0 MPa was investigated and revealed a complete separation of CO2 from the syngas. Furthermore, a cyclic absorption experiment confirmed good regeneration of the PIL, suggesting that it could be a potential material to separate and recover CO2 from syngas.