Dynamic covalent adaptive polymer network materials based on hindered urea bonds

Covalent adaptive polymeric networks covalently crosslinked with dynamic covalent bonds that undergo reversible exchange reaction hold good mechanical properties, dimensional stability, and solvent resistance as conventional thermosets and furthermore exhibit self-healability, reprocessability, sustainability and recyclability. Among many dynamic covalent bonds and interactions, hindered urea bond (HUB) that contains a bulky group on one of the two nitrogen atoms is promising for the development of dynamic covalent network materials. The developed HUB-bearing networks have been utilized for various applications requiring dynamic properties, such as energy harvesting and storage, sensor, flexible and wearable electronics, and surface coatings. This review summarizes the development of effective strategies to fabricate dynamic polymer networks based on HUBs with focus on the design and synthesis of effective HUBs with various bulkyamino groups as well as the synthesis of various polymeric materials.