the self‐healing strategies proposed by the authors' group are introduced, which are structured in accordance to the chemical reactions responsible for crack healing. Chapter 2 is dedicated to the healing reaction governed by addition polymerization and the self‐healing systems based microcapsules and plastic tubes as well, which are able to work without manual intervention. High healing efficiency, determined by static fracture, impact and fatigue tests, is acquired for epoxy composites. To improve healing speed and widen windows of processing and operation of self‐healing thermosetting materials, a few fast hardeners are introduced to work with epoxy monomer forming new groups of healing agent, as discussed in Chapter 3. Taking advantage of cationic polymerization, not only repair of cracks is possible at and below room temperature like the epoxy‐mercaptan pair, but also crack healing is greatly accelerated. Besides, redox cationic polymerization is used for healing of thermoplastics. Chapter 4 describes the self‐healing polymeric materials for advanced engineering applications, driven by anionic polymerization. The healing system consists of epoxy‐loaded microcapsules and imidazole latent hardener. The latter can be well pre‐dissolved in an uncured composites' matrix, leading to homogenous distribution of the reagent on a molecular scale. The major concern of Chapter 5 lies in usage of small molecule monomers as healing agent instead of epoxy monomer. Accordingly, nucleophilic addition, ring‐opening reaction, atom transfer radical polymerization, and free radical polymerization prove effective in rebinding the cracked planes. Unlike the extrinsic self‐healing approaches surveyed in Chapters 2–5, Chapter 6 deals with design, synthesis and characterization of intrinsic self‐healing epoxy, in which thermally reversible Diels–Alder bonds account for crack healing via chain reconnection. In addition to the remendability, the cured version of the novel epoxy has similar mechanical performance to conventional epoxy. In Chapter 7, the intrinsic self‐healing via reversible C─ON bonds is analyzed. Because of the synchronous fission/radical recombination of C─ON bonds, the polymers containing this type of reversible covalent bond can be self‐healed in a one‐step fashion, which prevents material distortion during healing as for those containing Diels–Alder bonds. Lastly, Chapter 8 demonstrates the application of reversible S─S bonds in self‐healing polymers. The disulfide bonds in the tailor‐made polymers as well as the commercial silicone elastomer and vulcanized rubber can be triggered under the stimuli of heating and sunlight, offering satisfactory healing efficiency.
It is our intention to emphasize integration of existing techniques and/or inventing novel synthetic approaches for application‐oriented material design and fabrication. Having gone through the book, readers would have a comprehensive knowledge of the field, while new researchers might have an idea of the framework for creating new materials or new applications. Readers from both academic and industrial communities will be provided with a grasp of the achievements to date and an insight into future developments. In addition, graduate students may be able to combine theories learnt in the classroom with practical research and development of materials. These are the goals of this book.
We would like to acknowledge support from the Natural Science Foundation of China (Grants 52 033 011, 51 773 229, 51 673 219, 51 333 008, and 51 873 235). We would also like to thank the team at John Wiley & Sons for their assistance throughout the publication process. In addition, we hope that the publisher is successful with this new book.
Ming Qiu ZhangMin Zhi Rong
Guangzhou, February 2021
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