An ethylene-propylene-diene rubber (EPDM), containing 5 wt% 5-ethylidene-2-norbornene, was functionalized with maleic anhydride through the Alder Ene reaction at temperatures above 200 degrees C in a co-rotating twin screw extruder. Characterization of the maleated product included FT-IR, H-1 and C-13 NMR and GPC. The degree of functionalization was determined by infrared analysis and by the mechanical properties of an ionic network formed by neutralizing the maleated rubber with zinc oxide. Increased temperature and maleic anhydride reactant concentration were found to improve the extent of reaction. Several Lewis acid species (SnCl2. 2H(2)O, RuCln. xH(2)O and AlCl3) were tested as catalysts, and they were found to have a small effect on the degree of functionalization. This effect improved with reduced acid concentration. Among the Lewis acids examined, AlCl3 gave rise to the greatest improvement of succinyl anhydride incorporation into the rubber.