Synthesis of artificial urushi via ring-opening reaction of benzoxazine with renewable cardanol

Abstract

A branched urushiol analogue (CBCP) was first prepared by a ring-opening reaction of a benzoxazine containing a phosphazene core with renewable cardanol under solvent-free and catalyst-free conditions. The structure of CBCP was identified using nuclear magnetic resonance (1H NMR, 13C NMR, 31P NMR) and Fourier transform infrared spectroscopy (FTIR) technique. The preparation process for the cured CBCP film was simple, and the curing reaction of CBCP was monitored using differential scanning calorimetry (DSC) and FTIR methods. CBCP undergoes cross-linking under ambient conditions, resulting in polymeric films (artificial urushi) that are optically transparent, scratch-free and wrinkle-free. The cured film, with a high hardness and glossy surface, showed excellent thermal, excellent adhesion to the metal substrates and good chemical resistances due to strong hydrogen-bonding interactions and a compact, highly cross-linking structure containing a hard phosphazene core. Interestingly, the limited oxygen index (LOI) of cured film is 30, suggesting that the artificial urushi has flame retardant performance.