Tailoring hypercrosslinked ionic polymers with high ionic density for rapid conversion of CO2 into cyclic carbonates at low pressure

•The HIPs with high ionic density (up to 3.01 mmol g−1) were synthesized through Friedel-Crafts alkylation of ionic monomers with multiple ionic pairs.•The ionic content and specific surface area of HIPs can be finely tuned by changing the type of ionic monomers and crosslinkers and their molar ratio.•The catalyst [HBIM-6]Br-DCX(3) exhibited excellent catalytic activity (90% yield) for cycloaddition of CO2 with styrene oxide at 120 ℃, 1 bar simulated flue gas (15% CO2 and 85 % N2) in 15 h.•The catalyst can be easily separable and maintained high reusability and stability after running five times.