Sustainable Citronellal-Derived Tetrafunctional Benzoxazines for High-Performance Corrosion-Resistant and Superhydrophobic Coating Applications

Citronellal containing tetrafunctional phenolic derivative was prepared to synthesize a series of multifunctional benzoxazines containing both biobased and synthetic amines, namely, furfurylamine (ffa), octadecylamine (oda), and (3-aminopropyl)triethoxysilane (aptes) through Mannich condensation reaction. High-resolution mass spectrometry (HRMS), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) techniques were used to determine the chemical structures. The lowest curing temperature was noted as 211 °C for RCL-oda by DSC analysis. Among the polybenzoxazines, poly(RCL-aptes) exhibited maximum thermal stability (Tmax = 435 °C), highest char yield (33%), limiting oxygen index (LOI = 30) and heat resistance index (HRI = 185 °C) values. Poly(RCL-aptes) possesses superhydrophobic behavior with a water contact angle of 157°, which demonstrated 98% oil–water separation efficiency. Poly(RCL-bz) exhibited a corrosion protection efficiency of 99% over the MS specimen, validated by DFT studies. Data obtained from different studies suggest that biobased polybenzoxazines possess water repellence and prove their utility toward high-performance coating applications under adverse environments.