Department of Pure and Applied Chemistry, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
ACS Macro Lett. 2023 Apr 18;12(4):462-467. doi: 10.1021/acsmacrolett.2c00737. Epub 2023 Mar 24.
Ionic interactions in ionic polymers, such as ionomers, polyelectrolytes, and polyampholytes, contribute to toughness in systems with high mobility and active ion dynamics, such as hydrogels and elastomers. However, it remains challenging to toughen rigid polymers through ionic interactions without lowering their elastic modulus through plasticization. Here, we present a strategy for toughening without sacrificing the elastic modulus by combining a comb polymer with bulky ammonium counterions. We designed and synthesized ionic comb polymers with oligoethylene glycol side chains and carboxylic acids in each monomer unit of the polynorbornene backbone, neutralized by trialkylamines, ranging from ethyl to octyl. The counterion size in ionic comb polymers influenced the mechanical properties of tensile testing─not the elongation at break and the elastic modulus but the ultimate strength and toughness. The ionic comb polymer containing heptylammonium counterions displayed the highest toughness of 77 MJ m. Tensile studies at various strain rates demonstrated a rate-dependent difference between heptyl- and octylammonium counterions. This result suggests that the heptylammonium counterion acted as a sacrificial bond by providing a moderate dissociation rate that was slightly slower than that of the octylammonium counterion, leading to toughening.
离子聚合物（如离聚物、聚电解质和聚两性电解质）中的离子相互作用有助于提高高迁移率和活性离子动力学系统（如水凝胶和弹性体）的韧性。然而，通过离子相互作用在不通过塑化降低弹性模量的情况下增强刚性聚合物仍然具有挑战性。在这里，我们提出了一种通过结合梳状聚合物和大体积铵抗衡离子来实现增韧而不牺牲弹性模量的策略。我们设计并合成了带有聚降冰片烯主链中每个单体单元中的聚乙二醇侧链和羧酸的离子梳状聚合物，并用三烷基胺中和，从乙基到辛基。离子梳状聚合物中的抗衡离子大小影响拉伸测试的力学性能-不是断裂伸长率和弹性模量，而是极限强度和韧性。含有庚基铵抗衡离子的离子梳状聚合物表现出最高的韧性为 77 MJ m。在不同应变速率下的拉伸研究表明，庚基和辛基铵抗衡离子之间存在速率依赖性差异。这一结果表明，庚基铵抗衡离子作为牺牲键发挥作用，提供的离解速率略低于辛基铵抗衡离子，从而实现增韧。
