A system for producing a functionalized olefinic-based polymer, the system comprising a polymerization zone for producing an olefinic-based polymer comprising a mixing section, a deliquifying section, and a quenching section, wherein at least one section of the polymerization zone has a defined cross-sectional area that continually decreases from a first end to a second end of said section; a devolatilization zone comprising a kneader or extruder, wherein said devolatilization zone is downstream of said polymerization zone and in fluid communication with said polymerization zone; and a functionalization zone downstream of said devolatilization zone and in fluid communication with said devolatilization zone.