Nonlinear rheology of poly(ethylene-co-methacrylic acid) ionomers

Using a parallel-plate rheometer equipped with a partitioned plate, and the Sentmanat extensional rheometer fixture, a full rheological characterization of several commercial ionomers 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 sticky-Rouse, that are associated with the characteristic lifetime of the ionic and hydrogen bonding associations. As such, scaling laws have been used to calculate the order of magnitude of the lifetimes of associations and the association energy that are important parameters to gain a better understanding of their rheological behavior. To study the effects of ionic associations, the commercial ionomers were completely unneutralized and their rheological behavior was compared directly with their associative counterparts. The rheological comparison included the linear viscoelastic moduli, the damping function, steady shear, and extensional rheology demonstrating the significant effects of ionic interactions.