Quadruple H-Bond Cross-Linked Polyimide for High Temperature Resistance, Corrosion Protection, and Self-Healing Coatings

Integrating multiple functions effectively into a single material poses significant challenges. The analysis of the synergistic enhancement mechanisms of multifunctional organic coatings is also quite complex. This study proposes a molecular cross-linking structural strategy to prepare multifunctional composite coatings, achieved through the synergistic effect of a dynamic cross-linking network formed by the ‘rigid-flexible’ polyimide (PI) and urea-enhanced quadruple H-bond cross-linked of 2-ureido-4[1H]-pyrimidinone (Upy). Electrochemical impedance spectroscopy analysis indicates that the prepared Upy-PI composite coating exhibits an impedance modulus as high as 1012 Ω·cm2 after being immersed in a 3.5 wt % NaCl solution for 3 days, which is 5 orders of magnitude higher than the impedance modulus of pure PI coating at 107 Ω·cm2. After thermal aging at 200 °C for 480 h, the Upy-PI still retains long-term corrosion resistance. DTG analysis shows that Upy-PI (Tmax = 528 °C) has an increase of 38 °C compared to pure PI (Tmax = 490 °C). Upy-PI exhibits outstanding mechanical properties, with a tensile stress of 9.32 MPa, which is 72 times that of pure PI coating. Further microscopic characterization results indicate that Upy-PI possesses excellent self-healing capabilities compared to pure PI coating. This study also analyzes the potential mechanisms for the synergistic enhancement of multiple properties, which may provide references for subsequent research in related fields.