Molecular structure design of polybenzoxazines with low surface energy and low modulus for marine antifouling application

The antifouling mechanism of low surface energy marine antifouling coatings is fouling release, and the key to fouling release is the adhesion strength of fouling organisms on the coating surface. Herein, we report an antifouling strategy to improve the fouling release performance of antifouling coatings by control the surface free energy and elastic modulus. Natural biomass cardanol-based benzoxazine monomers with different structures were designed by molecular structure and successfully synthesized via Mannich condensation. Detailed information of the chemical structure for the benzoxazines are analyzed by nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopies. In addition, the benzoxazines polymerization behavior is investigated by differential scanning calorimetry (DSC) analyses. The properties such as surface free energy and elastic modulus of polybenzoxazine were adjusted by the structure of the amine source. Notably, polybenzoxazines with octadecylamine as amine source have higher contact angle and lower surface free energy, and their elastic modulus is significantly lower than that of the octylamine benzoxazine. The elastic modulus of the octylamine benzoxazine was 732.5 MPa, while that of octadecylamine benzoxazine was only 24.0 MPa. Therefore, the polybenzoxazine coating has less fouling adhesion and exhibits better fouling release performance, and thus has better antifouling properties. This non-releasing polybenzoxazines without antifouling agent is a green, eco-friendly antifouling coating with low surface energy and low elastic modulus designed by molecular structure.