We have studied the effect of ionic interactions on the dynamics of polyamides in the molten state, both in the terminal relaxation regime and in the vicinity of the glass transition, using amorphous and end-blocked PA 6I polyamides. The density of interactions was varied by substituting different amounts of 5-sulfoisophthalic acid lithium salt. First, the effect of molecular weight distribution for PA 6I was studied in detail. As the molecular weight increased, a clear rubbery plateau appeared and the longest relaxation time was shifted to lower frequencies. The reference temperature used to construct the master curves was chosen to be T-g so that all master curves overlap in the glassy region. The main effect of introducing ionic groups was the increase in T-g by 10-40 degrees C. For comparable molecular weights, master curves of PA 6I and substituted polyamides overlapped in the complete range of frequencies when using an appropriate reference temperature. The reference temperature, at least up to 15 mol. %, seems to be correlated to the width of the glass transition that increases with increasing ionic content. The Rouse model was used to fit the viscoelastic response of all unentangled polyamides, showing that hydrogen bonds and/or ionic interactions did not play a role in the viscoelasticity of these polyamides in the molten state. The dynamic fragility indices determined from William-Landel-Ferry parameters decrease with increasing ionic content. Small-angle x-ray scattering measurements show that no segregation of ionic domains occurs in unentangled ionic copolyamides, while entangled ionic copolyamides show only weak segregation. (C) 2019 The Society of Rheology.