Zinc sulfonated EPDM of high (75 wt%) ethylene content behaves as an ionic thermoplastic elastomer. Diethylene glycol plasticizes the ionic domains of zinc sulfonated EPDM, without affecting the hydrocarbon backbone. Studies include measurement of physical properties, processability studies in a Monsanto processability tester (MPT), dynamic mechanical analyses (d.m.a.) and dielectric thermal analyses (d.e.t.a.). Copyright (C) 1996 Elsevier Science Ltd.