Sodium and zinc ionomers of sulfonated maleated EPDM rubber

Sulfonation of maleated EPDM (m-EPDM) rubber followed by its neutralization by sodium hydroxide or zinc acetate leads to the formation of an ionomer c onsisting of two types of ionic association, namely carboxylate and sulfona te anions with Na+ or Zn2+ as the counterion. The products were characteriz ed by infrared spectroscopic studies, dynamic mechanical thermal analyses, dielectric thermal analyses, and measurements of stress-strain properties. Results of dynamic mechanical analyses show that besides the rubbery platea u, there occurs two distinct mechanical loss peaks, of which one is associa ted with the glass-rubber transition and the other is due to the relaxation of the immobile polymer chains associated with the ionic aggregates and of ten referred to as the ionic relaxation, The upward shift of the glass tran sition temperature (T-g) refers to the formation of physical cross-links in the ionomer. Dielectric thermal analyses show that incorporation of the io nic groups causes profound changes in the dielectric constant (epsilon') of m-EPDM. Besides the glass-rubber transition in the low-temperature region, additional dipolar relaxation due to the ionic aggregates occur at a highe r temperature. Two types of ionic aggregate, namely multiplets and clusters , give rise to two values of the activation energy for the high-temperature dielectric relaxation. Incorporation of ionic groups causes improvement of physical properties of the polymer, as well as the retention of the proper ties at elevated temperatures (50 degrees C and 75 degrees C). The zinc ion omer shows higher strength at all temperatures than the sodium ionomer due to the greater extent of physical cross-linking arising from the ionic aggr egates.