Neighboring Molecular Engineering in Diels–Alder Chemistry Enabling Easily Recyclable Carbon Fiber Reinforced Composites

Abstract

Although a variety of dynamic covalent bonds have been successfully used in the development of diverse sustainable thermosetting polymers and their composites, solving the trade‐off between recovery efficiency and comprehensive properties is still a major challenge. Herein, a “one‐stone‐two‐birds” strategy of lower rotational energy barrier (Er) phosphate‐derived Diels‐Alder (DA) cycloadditions was proposed for easily recyclable carbon fiber (CF)‐reinforced epoxy resins (EPs) composites. In such a strategy, the phosphate spacer with lower Er accelerated the segmental mobility and dynamic DA exchange reaction for network rearrangement to achieve high‐efficiency repairing, reprocessing of the EPs matrix and its composites and rapid nondestructive recycling of CF; meanwhile, incorporating phosphorus‐based units especially reduced their fire hazards. The resulting materials simultaneously showed excellent thermal/mechanical properties, superb fire safety and facile recyclability, realizing the concept of recycling for high‐performance thermosetting polymers and composites. This strategy is of great significance for understanding and enriching the molecular connotation of DA chemistry, making it potentially applicable to the design and development of a wide range of dynamic covalent adaptable materials toward practical cutting‐edge‐tech applications.

Recycling of Epoxy Resins with Degradable Structures or Dynamic Cross-Linking Networks: A Review

“…Therefore, thermosets introducing D–A addition structures have similar thermoplasticity to thermoplastic under heating conditions. The thermosets made in this way are quickly and conveniently degraded, reshaped, or self-healed . In the early 21 st century, Tian et al used bis-maleimide and furan monomers containing epoxy group to prepare epoxy prepolymers containing D–A reversible units.…”

“…The thermosets made in this way are quickly and conveniently degraded, reshaped, or self-healed. 140 In the early 21 st century, Tian et al 141 used bis-maleimide and furan monomers containing epoxy group to prepare epoxy prepolymers containing D−A reversible units. The cured EPR not only has mechanical properties comparable to commercial EPR, but also can achieve crack self-healing at low temperatures without the need for additional catalysts.…”

Ligand Dissociation of Metal-Complex Photocatalysts toward pH-Photomanipulation in Dynamic Covalent Hydrogels for Printing Reprocessable and Recyclable Devices

“…Such hydrogel polymers with dynamic properties primarily contain reversible covalent bonds capable of exchanging, dissociating, or switching in response to various stimuli, giving rise to constitutional dynamics. − Thus, designing reversible reactions to create dynamic bonding is crucial for preparing high-performance dynamic covalent polymers. Typically, the bonding interactions generated via dynamic chemistries, − like Diels–Alder and reshuffling reactions, transesterification, and photoresponsive dimerization, offer stable polymer networks at normal states and outstanding reversibility under heating and UV-light irradiation. These bonds enable hydrogels to regulate dynamic behaviors rapidly and efficiently.…”