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Poly(ethylene-co-methacrylic acid) (EMAA) partially neutralized by metal ions such as sodium or zinc is one of the most widely used ionomers. Structure and mechanical properties in the solid state of these ethylene ionomers have been extensively investigated, and a review book was recently published.1) Viscoelastic properties of sodium or zinc ethylene ionomer melts have also been studied to clarify the role of ions in the molten state.2-4 ) Especially, Vanhoorne and Register5) studied the effect of the protons of unneutralized acid groups on the melt rheology of partially neutralized EMAA ionomers. By removing the protons by etherification of the acid group, they have found that the role of the protons in sodium ionomers is different from that in zinc ionomers.5) In the case of sodium ionomers, a sodium ion is not only paired with one COO but also coordinated with two COOH acid groups, and the sodium ion and a proton can be exchanged between COONa and COOH. This “acid-cation exchange” mechanism5 ) allows a polymer segment to easily diffuse from one ion aggregate to others, and lowers the friction for the segmental motion. In the case of zinc ionomers, on the other hand, a zinc ion is coordinated with two COO groups, and no COOH group exists near the ion. Thus the acid-cation exchange does not take place, and the zinc ionomer has much higher viscosity (and longer relaxation time) than the sodium ionomers at equivalent neutralization. In this paper, in order to get deeper insight into the role of ions in the melt rheology, dynamic shear moduli of two series of blends, (1) blends of EMAA and EMAA sodium ionomer,and (2) blends of EMAA sodium and zinc ionomers, were examined as a function of the blend ratio. In the case of the former blends, the zero shear viscosity as a function of composition followed the log additively rule, while a strong negative deviation from the log additively rule was observed in the latter blends. A possible explanation of this finding will be given.

Composition Dependence of Viscosity of Ethylene Ionomer Blends.