Elongational Rheology of Entangled Ionomers Based on Poly(hexyl methacrylate)

Linear viscoelasticity (LVE) and nonlinear elongational behavior are examined for a series of entangled ionomers based on poly(hexyl methacrylate) as the backbone and sodium sulfonate as the ionic group. The ion content varies in a wide range, enabling our examination to cover a wide range of degrees of gelation from sol chains to mixtures of sol chains and gel networks and to gel networks having different strand densities. Analysis of the LVE enables quantification of the effective degree of gelation & varepsilon;(eff). For all samples examined, the elongational behavior obeys better the prediction of the neo-Hookean model with increasing Weissenberg number Wi defined as a product of the elongational rate and the terminal relaxation time. The elongational behavior is compared for samples with different & varepsilon;(eff) at the normalized Wi, where the hardening strengthens and the stretchability reduces with increasing & varepsilon;(eff). These trends suggest that the pristine network structure is more maintained during the elongational flow for the samples having higher ion content, which is directly linked to the role of the ionic association in tethering the network strands.