Quaternary Ammonization Treatment Enhances the Antifouling Activities of Capsaicin-Based Polybenzoxazine Coatings

Marine biofouling is an important factor that affects the service life of marine equipment. In this work, phenol source capsaicin-mimicking <i>N</i>-(4-hydroxy-3-methoxy-benzyl) acrylamide, two amine sources, 3-aminopropyltriethoxysilane (APTES) and furfurylamine (FFA), together with paraformaldehyde were used to prepare two benzoxazine coatings, P(HA) and P(HF). By reaction with iodomethane, the quaternary ammonium group was introduced into the N position of the oxazine ring. Quaternarily ammonified benzoxazine coatings P(HAI) and P(HFI) show exciting antibacterial performance compared to that of the untreated benzoxazine coating. The P(HFI) coating exhibited 93.8%, 96.4%, 99.9%, and 99.9% killing rates for <i>Escherichia coli</i>, <i>Staphylococcus aureus</i>, <i>Pseudomonas aeruginosa</i>, and <i>Bacillus subtilis</i>, respectively. The quaternary ammonization treatment also precipitated further enhanced anti-alga activity and excellent real-sea antifouling performances. However, the introduction of the ionic groups hindered the thermal polymerization of benzoxazine, leading to more defects on the coating surface, resulting in corrosion resistance that was poorer than that of HA and HF as detected from electrochemical corrosion and neutral salt spray experiments. The corrosion current density of the P(HA) and P(HF) coatings is 2 orders greater than that of the P(HAI) and P(HFI) coatings. Our results shed light on developing new quaternary ammonization treatment routes for polymeric coatings for the desired functions.