Force–reversible chemical reaction at ambient temperature for designing toughened dynamic covalent polymer networks

Abstract

Force-reversible C-N bonds, resulting from the click chemistry reaction between triazolinedione (TAD) and indole derivatives, offer exciting opportunities for molecular-level engineering to design materials that respond to mechanical loads. Here, we displayed that TAD-indole adducts, acting as crosslink points in dry-state covalently crosslinked polymers, enable materials to display reversible stress-responsiveness in real time already at ambient temperature. Whereas the exergonic TAD-indole reaction results in the formation of bench-stable adducts, they were shown to dissociate at ambient temperature when embedded in a polymer network and subjected to a stretching force to recover the original products. Moreover, the nascent TAD moiety can spontaneously and immediately be recombined after dissociation with an indole reaction partners at ambient temperature, thus allowing for the adjustment of the polymer segment conformation and the maintenance of the network integrity by force-reversible behaviors. Overall, our strategy represents a general method to create toughened covalently crosslinked polymer materials with simultaneous enhancement of mechanical strength and ductility, which is quite challenging to achieve by conventional chemical methods.

Structure–Reactivity–Property Relationships in Covalent Adaptable Networks

“…We also envision that the marriage of mechanochemistry 141 and CANs will enable an exciting new class of materials whose dynamic properties change as a function of force. 142 As physical organic and synthetic chemists working in the field of CANs, we offer below several recommendations for future studies that seek to develop these structure−reactivity−property relationships. Furthermore, we suggest advances in measurement science that would greatly impact this field by enabling direct measurement of cross-link reactivity in CANs.…”

Citric acid-induced room temperature self-healing polysiloxane elastomers with tunable mechanical properties and untraditional AIE fluorescence

“…The healing efficiencies of both IU-PAM and IU-PDMS could reach ∼ 100% after being healed at room temperature for 24 h. 23 Furthermore, polymers applied in other fields (e.g., luminescence) also call for excellent self-healing properties to meet specific usage requirements. 36,37 For example, Lei et al prepared a class of self-healing and photoluminescence waterborne polyurethane coatings. The molecular structure of polymine (PEI) containing primary and secondary amines can form ionic and hydrogen bonds with previously prepared carboxyl-type waterborne polyurethanes (CWPU).…”

Unexploited Design and Application of Dynamic Covalent Networks: Phenol-yne Click Reaction and Porous Film Generation

“…Several reported examples include Diels− Alder reaction, 16 thio/aza-ene Michael addition, 17,18 thiopiopolates/Meldrum's acid addition, 19 amino-yne click reaction, 20,21 and triazolinedione-indole addition. 22 Exploring new click reactions for dynamic covalent polymers not only expands the tool box but also offers new dynamic properties.…”

“…Reversible/dynamic click reactions have been demonstrated useful for the fabrication of dynamic covalent networks (DCNs) that can be dissembled or recycled on demand. Several reported examples include Diels–Alder reaction, thio/aza-ene Michael addition, , thio-piopolates/Meldrum’s acid addition, amino-yne click reaction, , and triazolinedione-indole addition . Exploring new click reactions for dynamic covalent polymers not only expands the tool box but also offers new dynamic properties.…”