A process for preparing polymeric compounds comprising ionic imidazolium groups (polymeric imidazolium compounds for short) comprising reacting —an α-dicarbonyl compound, —an amino compound having at least two primary amino groups (referred to as oligoamine), —a protic acid, —less than 1 mol of a compound with only one aldehyde group (referred to as monoaldehyde) per mol of oligoamine and —optionally further compounds.