Constructing Thermally Reversible Dynamic Hydrogels via Catalysis-Free Knoevenagel Condensation.

Thermally reversible dynamic covalent bonds (TRDCBs) have attracted great interest for building polymers with self-healing and adaptable properties in bulk. However, none of the developed TRDCBs can be used in aqueous media for the fabrication of thermally reversible dynamic hydrogels due to the requirement of high temperature to initiate the retro-reaction or the susceptibility to hydrolysis. Herein, we report a thermally reversible dynamic covalent C═C double bond that was formed by catalysis-free Knoevenagel condensation (CKC) between benzaldehyde and cyanoacetate end-functionalized polymers in aqueous solution. The as-formed TRDCB shows typical thermal reversibility in the aqueous media under mild temperatures (4-70 °C). Constructing hydrogels with this TRDCB led to the formation of thermally reversible dynamic hydrogels with intriguing self-healing, injectable, thermosensitive, and thermoplastic properties. Overall, this work not only broadens the application of TRDCBs in aqueous media but also provides a thermally reversible dynamic hydrogel for potential use in various biomedical fields.