Reactive blending of 1,3-benzoxazines and 1,3,5-triazinanes for durable thermosets with enhanced adhesion, acid resistance and chemical stability

The development of high-performance thermosets with enhanced chemical and mechanical properties is critical for demanding applications. This study reports a novel reactive blending approach to synthesize polybenzoxazine-triazinane copolymers as hybrid thermosets by combining 1,3,5-triazinanes with 1,3-benzoxazines. Polymer networks were prepared via a cost effective and one-pot synthesis using 4,4 '-oxydianiline (ODA) and bisphenol A-aniline-based benzoxazine (BA-a). The resulting BA-a/ODA-PHT hybrids exhibit significantly improved acid resistance and 91 % of their mass retained after 30 days in 0.1 M HCl. In contrast, pristine ODA-PHT retained only 40 % by mass. Additionally, the hybrids show a fourfold increase in adhesion to mild steel (4.61 MPa vs. 0.99 MPa for ODA-PHT) and excellent resistance to aggressive liquids, including hydraulic fluids, motor oil, and jet fuel. Thermogravimetric analysis reveals enhanced thermal stability, with a char yield of similar to 35 % at 800 degrees C for BA-a/ODA-PHT. Spectroscopic and thermal analyses including nuclear magnetic resonance (NMR), Fourier-transform infrared (FT-IR), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) were used for further characterizations.