Even under low external force,a few macromolecules of a polymer have to be much more highly stressed and fractured first due to the inherent heterogeneous microstructure.When the materials keep on working under loading,as is often the case,the minor damages would add up,endangering the safety of use.Here we show an innovative solution based on mechanochemically initiated reversible cascading variation of metal-ligand complexations.Upon loading,crosslinking density of the proof-of-concept metallopolymer networks autonomously increases,and recovers after unloading.Meanwhile,the stress-induced tiny fracture precursors are blocked to grow and then restored.The entire processes reversibly proceed free of manual intervention and catalyst.The proposed molecular-level internal equilibrium prevention mechanisms fundamentally enhance durability of polymers in service.