Repeated Intrinsic Self-Healing of Wider Cracks in Polymer via Dynamic Reversible Covalent Bonding Molecularly Combined with a Two-Way Shape Memory Effect

To enable repeated intrinsic self-healing of wider cracks in polymers, a proof-of-concept approach is verified in the present work. It operates through two-way shape memory effect (SME)-aided intrinsic self-healing. Accordingly, a reversible C-ON bond is introduced into the main chain of crosslinked polyurethane (PU) containing an elastomeric dispersed phase (styrene-butadiene-styrene block copolymer, SBS). The PU/SBS blend was developed by the authors recently, and proved to possess an external stress free two-way SME after programming. As a result, the thermal retractility offered by the SME coupled with the reversible C-ON bonds can be used for successive crack closure and remending based on synchronous fission/radical recombination of C-ON bonds. Moreover, multiwalled carbon nanotubes are incorporated to impart electrical conductivity to the insulating polymer. Repeated autonomic healing of wider cracks is thus achieved through narrowing of cracks followed by chemical rebonding under self-regulating Joule heating. No additional programming is needed after each healing event, which is superior to one-way SME-assisted self-healing. The outcomes set an example of integrating different stimuli-responsivities into single materials.

为了使聚合物中更宽的裂缝能够反复进行内在自愈合，本研究验证了一种概念验证方法。它通过双向形状记忆效应（SME）辅助的内在自愈合来实现。因此，在含有弹性体分散相（苯乙烯 - 丁二烯 - 苯乙烯嵌段共聚物，SBS）的交联聚氨酯（PU）主链中引入了可逆的C - ON键。作者最近开发了PU/SBS共混物，并证明其在编程后具有无外部应力的双向形状记忆效应。结果，形状记忆效应提供的热收缩性与可逆的C - ON键相结合，可基于C - ON键的同步裂变/自由基重组用于连续的裂缝闭合和修复。此外，加入多壁碳纳米管使绝缘聚合物具有导电性。因此，通过裂缝变窄，然后在自调节焦耳热作用下进行化学键合，实现了更宽裂缝的反复自主愈合。每次愈合事件后不需要额外的编程，这优于单向形状记忆效应辅助的自愈合。这些成果为将不同的刺激响应性集成到单一材料中树立了榜样。