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, $f_{\mathrm{ion}}\cong 4$, but a varied number of hydrogen bonds per chain, f_H = 5.5–27. The stretchability that is reflected in the maximum Hencky strain achieved before rupture shows nonmonotonous change with f_H: the stretchability improves with increasing f_H from 5.5 to 14 while it decreases upon further increasing f_H 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 f_H, which probably leads to the decrease of stretchability at high f_H = 27.

中文翻译：

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通过调节二次相互作用的密度提高缔合聚合物的拉伸性a)

离聚物熔体的宏观拉伸性强烈依赖于拉伸流动过程中的结构演变。已经注意到引入比离子缔合弱的二级缔合可以提高拉伸性。为了解该机制，本研究考察了每条链含有固定数量离子基团的未缠结离聚物的拉伸性，$F_{\mathrm{离子}}\cong \mathrm{4个}$，但每条链的氢键数量不同，f _H  = 5.5–27。在断裂前达到的最大亨基应变中反映的可拉伸性显示出随f _H的非单调变化：可拉伸性随着f _{H从 5.5 增加到 14 而提高，而随着}f _H的进一步增加而降低到 27. 前者的改进归因于离子基团应变诱导解离后链收缩的减慢。减速会抑制可能长入裂缝的缺陷或小裂纹的形成。这种机制，即应变诱导解离后链收缩，仅在伸长速率快于离子解离速率但慢于链收缩速率的窗口中成立。该窗口随着f _H的增加而变窄，这可能导致高f _H  = 27 时的拉伸性降低。