The　one-pot　synthesis　of　3-aryl-2-oxazolidinone　from　carbon　dioxide　(CO2),　epoxides,　and　aniline　represents　a　promising　strategy　for　CO2utilization.　However,　the　efficiency　remains　far　from　adequate　for　industrial　deployment,　primarily　due　to　the　absence　of　purpose-designed　catalysts.　Herein,　a　dual-anion-rich　(Br–and　OAc–)　polymeric　ionic　liquid　(P-TBTOD-1/1/2)　was　synthesized　via　copolymerization　of　vinyl-functionalized　ionic　liquids　(ILs),　1,1,3,3-tetramethylguanidine　bromide　([AlTMG]Br),　and　1,1,3,3-tetramethylguanidine　acetate　([AlTMG]OAc),　with　divinylbenzene　(DVB).　The　catalytic　performance　was　evaluated　for　the　synthesis　of　3-phenyl-2-oxazolidinone　from　CO2,　ethylene　oxide　(EO),　and　aniline　in　a　batch　autoclave　at　2.5　MPa　and　110　°C　with　a　catalyst　dosage　of　4　wt　%　(based　on　aniline)　for　1.0　h.　The　aniline　conversion　was　100%,　and　the　yield　of　3-phenyl-2-oxazolidinone　was　75%.　While　Br–could　effectively　promote　the　cyclization　reaction　between　CO2and　EO　to　form　ethylene　carbonate　(EC),　its　catalytic　efficiency　in　the　subsequent　conversion　of　2-(phenylamino)ethanol　and　EC　to　3-phenyl-2-oxazolidinone　was　limited.　In　contrast,　OAc–exhibited　significantly　superior　catalytic　performance　in　this　reaction.　OAc–effectively　activated　aniline　and　EO　to　generate　2-(phenylamino)ethanol.　The　accumulation　of　2-(phenylamino)ethanol　and　EC　in　the　reaction　system　synergistically　drove　the　equilibrium　toward　product　formation,　thereby　significantly　enhancing　the　overall　yield　of　3-phenyl-2-oxazolidinone.　Additionally,　P-TBTOD-1/1/2　exhibited　outstanding　stability,　maintaining　the　yield　of　3-phenyl-2-oxazolidinone　almost　unchanged　after　five　consecutive　runs.　These　findings　indicate　that　P-TBTOD-1/1/2　is　a　promising　candidate　catalyst　for　CO2utilization.　©　2025　American　Chemical　Society