Hindered urea bonds for dynamic polymers: An overview

Polymers bearing dynamic covalent bonds have gained great attention over the last decades owing to their self-healing, shape memory, and environmental adaptation properties. However, most of them require a catalyst or the environmental conditions to be amended before bond reversion and exchange reactions can be realized. This review paper delineates the hindered urea bonds (HUBs) with unique reaction dynamics, which are developed for the preparation of catalyst-free and reconfigurable polyureas and poly(urethane-urea)s at low temperatures. Herein, the rational design of HUBs, the kinetics, and the primary motivations of self-healing and thermosets reprocessing by changing the dynamic topological configuration are discussed. The recent progress in developing polyurea and poly(urea-urethane)s based on HUBs for multifunctional applications is also highlighted. Additionally, the challenges and the future perspectives of HUBs are also captured. The dynamic HUBs open up a promising way to low-cost, facile processed polymers, and as well provides new opportunities in material innovations.