Ions in Polymers

Metal sulfonate groups were introduced into an ethylene-propylene-diene monomer terpolymer (EPDM) via reaction of its residual unsaturation with acetyl sulfate, followed by neutralization of the resultant polymeric sulfonic acid with ometal acetates. The composition, structure, and molecular weight of the EPDM and the sulfonate content, cation borne by the sulfonate group, and metal acetate concentration of the ionomer were found to substantially affect the rheological and mechanical properties of the ionomer. Through the proper selection of EPDM backbone, EPDM molecular weight, and sulfonate content, and through the use of the zinc cation, it was possible to prepare EPDM-based ionomers with excellent mechanical properties and with the lowest possible melt viscosities. Although formulations derived from these zinc sulfonate-containing EPDM's possess melt viscosities that are higher than desirable for facile processability, in many respects they are truly thermoplastic elastomers.