Polymers bearing dynamic covalent bonds may exhibit dynamic properties,such as self-healing,shape memory and environmental adaptation.However,most dynamic covalent chemistries developed so far require either catalyst or change of environmental conditions to facilitate bond reversion and dynamic property change in bulk materials.Here we present the rational design of hindered urea bonds(HUBs)(urea with bulky substituent attached to its nitrogen)and the use of HUBs to make polyureas and poly(urethane-ureas)capable of catalyst-free dynamic property change and autonomous repairing at low temperature.Given the simplicity of the HUB chemistry(reaction of a bulky amine with an isocyanate),incorporation of the catalyst-free dynamic covalent urea bonds to conventional polyurea or urea-containing polymers that typically have stable bulk properties may further broaden the scope of applications of these widely used materials.