Using a parallel-plate rheometer equipped with a partitioned plate and the Sentmanat extensional rheometer fixture, a full rheological characterization of several commercial ionomers (sodium and zinc) and their corresponding parent copolymers has been carried out. Particular emphasis has been placed on the distribution of the relaxation times to identify the characteristic times, such as reptation, Rouse, and lifetime of associations that are associated with entanglements, ionic and hydrogen bonding associations. As such, scaling laws have been used to calculate the order of magnitude of these characteristic times that are important parameters to gain a better understanding of their rheological behavior. To study the effects of ionic reversible associations, the commercial ionomers were completely un-neutralized and their rheological behavior was compared directly with their associative counterparts. The rheological comparison included the linear viscoelastic moduli, the damping function, and extensional rheology, demonstrating the significant effects of ionic interactions. Moreover, the rheological properties of sodium and zinc ionomers are also compared addressing the effect of valency of ions (Na⁺ vs Zn⁺⁺).

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The capillary flow properties of several commercial ionomers (sodium and zinc) were studied to assess their processability in terms of instabilities such as wall slip and melt fracture. Using capillary dies of various diameters and lengths to control capillary extrusion pressure, it was found that the viscosity of these polymers exhibits a relatively small dependence on pressure, more importantly at relatively smaller pressures. Using capillaries of various diameters at fixed length-to-diameter ratios, it was also found that the no-slip boundary condition is a valid assumption for these polymers due to the strong ionic associations and strong interactions with the capillary wall. All ionomers were found to exhibit gross melt fracture (no sharkskin), a phenomenon more dominantly observed at lower temperatures. The occurrence of gross melt fracture and the absence of surface (sharkskin) melt fracture is a characteristic of extensional strain-hardening polymers, noting that all ionomers examined exhibit this phenomenon. The critical shear stress for the onset of gross melt fracture was found to depend on the lifetime of associations, τ_S (${\tau }_S\propto {\left(Z_E/Z_S^2\right)}^{1/5}$ , where Z_E is the number of entanglements and Z_S is the number of associations), independent of temperature, molecular weight, and type of ion (zinc or sodium).