Constructing Self‐Strengthening High‐Temperature and Corrosion‐Resistant Polyurea Coatings via Weak‐To‐Strong Bond Conversion

ABSTRACT Conventional polymer coatings often fail in harsh environments due to structural instability at elevated temperatures and insufficient salt corrosion resistance. Here we establish a thermally triggered weak‐to‐strong bond conversion strategy to create filler‐free, transparent polyaspartic polyurea (PAPU) coatings from low‐cost industrial feedstocks, polyaspartic esters and polyisocyanate. Upon heating, hindered urea linkages in PAPU irreversibly convert to rigid hydantoin rings, enhancing crosslinking density and chain rigidity without unstable moieties or fillers. The optimized formulation maintains excellent mechanical properties (tensile strength > 50 MPa, Young's modulus 1.2–1.4 GPa) after 72 h at 200°C, with T g increasing from 48°C to 118°C. It exhibits ultrahigh lap shear strength (26.1 MPa) on steel, surpassing most high‐performance adhesives. In a 4‐week salt spray test, its low‐frequency impedance modulus (|Z| 0.01 Hz ) remains 4.29 × 10 1 1 Ω·cm 2 , outperforming silicone‐based and composite coatings reported previously. The “weak‐to‐strong” mechanism provides a versatile design strategy for high‐performance polymeric materials. This work demonstrates an in‐situ bond conversion route to self‐reinforcing, heat‐resistant, and corrosion‐protective polymer coatings, offering a generalizable design principle for extreme‐environment materials.