Improving stretchability of associative polymers through tuning density of the secondary interactionsa)

Abstract

The macroscopic stretchability of ionomer melts strongly relies on the structural evolution during the elongational flow. It has been noted that the introduction of the secondary associations weaker than the ionic association can improve the stretchability. To understand the mechanism, this study examines the stretchability of unentangled ionomers containing a fixed number of ionic groups per chain, fion≅4, but a varied number of hydrogen bonds per chain, fH = 5.5–27. The stretchability that is reflected in the maximum Hencky strain achieved before rupture shows nonmonotonous change with fH: the stretchability improves with increasing fH from 5.5 to 14 while it decreases upon further increasing fH to 27. The former improvement is attributed to the slowing down of chain retraction after the strain-induced dissociation of ionic groups. The slowing down would suppress the formation of defects or small cracks that potentially grow into the fracture. This mechanism, i.e., strain-induced dissociation followed by the chain retraction, holds only in a window where the elongational rate is faster than the ionic dissociation rate but slower than the chain retraction rate. This window narrows down with increasing fH, which probably leads to the decrease of stretchability at high fH = 27.