A reactive extrusion process for producing an ionomer is disclosed. The process comprising adding a polymer containing a carboxyl functionality to an extruder, then homogenously melting the polymer in a melting zone of the extruder. A first melt seal zone of the extruder is formed to separate the melting zone from an injection zone where an aqueous solution of metallic ions are added to the molten polymer. The first melt seal zone is formed by increasing the pressure in the melt seal zone to a pressure which is higher than the vapor pressure of the water at any point in the injection zone and the reaction zone. The aqueous solution of metallic ions is then mixed with the polymer containing the carboxyl functionality in a reaction zone of the extruder under conditions such that the metallic ions are substantially reacted with the carboxyl functionality. A pressure build-up zone is formed in the extruder, wherein the pressure build-up zone is located no earlier than at the end of the reaction zone wherein the pressure build-up zone is formed by increasing the pressure to a level such that the aqueous solution of metallic ions remains in the liquid phase for a time sufficient to allow for the desired reaction between the metallic ions and the carboxyl functionality of the polymer.