Bio‐Based Azine‐Functional Polyurethane Networks as Multifunctional Coatings: Nonconventional Luminescence and High‐Efficiency Corrosion Protection of Steel

ABSTRACT Developing sustainable polymer networks that integrate robust barrier performance with additional functional responses is an important goal in contemporary polymer science. In this work, bio‐based segmented polyurethane networks (PUPH1–PUPH3) are prepared from castor‐oil‐derived polyols and an azine‐modified castor‐oil derivative, crosslinked with poly(hexamethylene diisocyanate) (pHMDI), to elucidate how network architecture governs thermal stability, anticorrosion behavior, and nonconventional luminescence. By systematically varying the hard/soft segment ratios, the crosslink density and segmental packing are tuned. Fourier‐transform infrared spectroscopy and X‐ray diffraction confirm complete urethane formation and predominantly amorphous segmented networks, while scanning electron microscopy reveals smooth, defect‐poor morphologies for the most crosslinked compositions. Thermogravimetric analysis shows 5 wt% weight‐loss temperatures of 307°C–314°C, evidencing enhanced thermal robustness. Electrochemical measurements in 1.0 M H 2 SO 4 demonstrate that the optimized network markedly suppresses the corrosion current density of mild steel, achieving an inhibition efficiency of 99.55% and a significant increase in charge‐transfer resistance, attributed to a dense, highly resistive interfacial barrier. Solid‐state photoluminescence measurements further reveal excitation‐dependent, cluster‐type emission arising from densely packed heteroatom‐rich segments. These findings establish clear correlations between molecular/network design and multifunctional properties in castor‐oil‐based polyurethane networks, highlighting a renewable platform for advanced polymeric coatings.