A process for preparing polymeric, ionic compounds comprising imidazolium groups (polymeric, ionic imidazolium compounds for short) comprising reacting an a-dicarbonyl compound, an aldehyde, —at least one amino compound having at least two primary amino groups (referred to as oligoamine), if appropriate an amino compound having only one primary amino group (referred to as monoamine) and a protic acid, wherein the protic acid is placed in the reactor and the oligoamine or the aldehyde and o dicarbonyl compound or the oligoamine, the aldehyde and α-dicarbonyl compound are fed to the protic acid.