Miwa Yohei, Kurachi Junosuke, Sugino Yusuke, Udagawa Taro, Kutsumizu Shoichi
Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193, Japan and PRESTO, Japan Science and Technology Agency, Japan.
Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University, Yanagido, Gifu 501-1193, Japan.
Soft Matter. 2020 Apr 8;16(14):3384-3394. doi: 10.1039/d0sm00058b.
To compromise high mechanical strength and efficient self-healing capability in an elastomer with dynamic crosslinks, optimization of the molecular structure is crucial in addition to the tuning of the dynamic properties of the crosslinks. Herein, we studied the effects of molecular weight, content of carboxy groups, and neutralization level of ionically crosslinked polyisoprene (PI) elastomers on their morphology, network rearrangement behavior, and self-healing and mechanical properties. In this PI elastomer, nanosized sphere-shaped ionic aggregates are formed by both neutralized and non-neutralized carboxy groups that act as stickers. The number density of the ionic aggregates that act as physical crosslinks increased with increase in the stickers' concentration, although the size of the ionic aggregates was independent of the molecular weight and the stickers' concentration. The ionic network was dynamically rearranged by the stickers' hopping between the ionic aggregates, and the rearrangement was accelerated by decreasing the neutralization level. We found that the 2Rg of the PI must be significantly larger than the average distance between the ionic aggregates to obtain a mechanically strong PI elastomer. We also found that further increase in the molecular weight is effective to enhance the dimensional stability of the elastomer. However, this approach reduced the elastomer's self-healing rate at the same time because the diffusion and randomization of the polymer chains between the damaged faces were reduced. In this work, we clearly demonstrated the principle in the optimization of the molecular structure for the ionically crosslinked PI elastomers to tune the mechanical and autonomous self-healing properties.
为了在具有动态交联的弹性体中兼顾高机械强度和高效自修复能力，除了调节交联的动态性能外，分子结构的优化至关重要。在此，我们研究了离子交联聚异戊二烯（PI）弹性体的分子量、羧基含量和中和程度对其形态、网络重排行为以及自修复和机械性能的影响。在这种PI弹性体中，纳米级球形离子聚集体由充当“贴纸”的中和和未中和羧基形成。充当物理交联的离子聚集体的数量密度随着“贴纸”浓度的增加而增加，尽管离子聚集体的尺寸与分子量和“贴纸”浓度无关。离子网络通过“贴纸”在离子聚集体之间的跳跃而动态重排，并且通过降低中和程度加速重排。我们发现，PI的2Rg必须显著大于离子聚集体之间的平均距离才能获得机械强度高的PI弹性体。我们还发现，进一步增加分子量对于提高弹性体的尺寸稳定性是有效的。然而，这种方法同时降低了弹性体的自修复速率，因为受损面之间聚合物链的扩散和随机化减少了。在这项工作中，我们清楚地证明了优化离子交联PI弹性体分子结构以调节机械和自主自修复性能的原理。
