High-Performance Self-Healing Polymers

Conspectus Self-healing ability is one of the most attractive features of biological tissues, as it helps living creatures to recover physiological functions and prolongs their lifespans after unexpected injuries. Inspired by this feature, self-healing artificial polymers have been developed based on extrinsic and intrinsic designs since the 1950s. In particular, the intrinsic self-healing polymers have received enormous attention since 2001 because of their unlimited self-healing times and easy preparation. Therefore, many excellent works are reported, and our understanding of the self-healing polymer goes deeper and deeper. Self-healing is the process of the rejoining of the dynamic bonds/interactions. Therefore, the healing process involves two critical factors. One is the dynamic nature of dynamic bonds/interactions. The other is the high mobility of the polymer chains. However, the dynamic bonds/interactions are vulnerable to external forces and environmental stimuli because their bond energy is lower than that of the covalent bonds, which leads to several innate drawbacks of intrinsic self-healing polymers, such as poor mechanical properties (low fracture strength, low fracture strain, low modulus, and low fracture toughness) and poor resistance against the external environment (vulnerable to acid, alkali, or moisture). Also, since high chain mobility is also a prerequisite for intrinsic self-healing, most polymers cannot be healed in the glassy state where the polymer chains are frozen. Therefore, it is challenging to develop high-performance self-healing polymers, which not only possess high mechanical strength, toughness, and stability under ambient conditions or severe environments but also manifest high self-healing efficiency in the rubbery state or even in the glassy state. Therefore, how to overcome this challenge has become a hot topic in the field of self-healing polymers. To address the above problem, many high-performance self-healing polymers with high mechanical properties, high self-healing ability, or high environmental stability are published by using different strategies. These strategies are effective at enhancing the mechanical properties or increasing its environmental stability and are worth learning about. Our group has carried out some work in this field. In this Account, we highlight our works toward fabricating high-performance self-healing polymers. We summarize the high-performance self-healing polymers from three aspects: self-healing polymers with high mechanical properties (such as high toughness, tensile strength, stretchability, and modulus), glassy polymers capable of self-healing in the glassy state, and environmentally stable self-healing polymers. In particular, strategies based on tailoring molecular-level structure, condensed structure, and filler reinforcement are discussed in detail to construct self-healing polymers with high mechanical properties. Finally, the future development of intrinsic self-healing polymers is examined from the perspective of practical application and fundamental research.