Rheological Properties of Poly(ethylene-co-ethylacrylate) Based Ionomers in the Absence of Acid Groups

The melt rheological properties of ionomers prepared by partial saponification of poly(ethylene-co-ethylacrylate) (EEA) with potassium hydroxide were investigated by using dynamic shear and uniaxial elongation experiments. Molecular design of the present EEA-based ionomers eliminated acid groups which decrease melt viscosity of conventional ionomers. Dynamic viscoelastic results showed that ERA ionomers had a high shear modulus even in the low frequency region. Uniaxial elongation viscosity showed strain hardening of the EEA ionomers, whereas, on the other hand, ERA, which is the base polymer of the present ionomers, showed strain softening. These results can be explained by ionic cross-linking effects mediated by ion aggregates in the absence of acid group. We discuss the unique role of acid groups in ionomers.