Design, Synthesis, and Evaluation of Benzoxazine Copolymers for Anti-Corrosion Coating Applications Based on Improved High Crosslinking Density and Hydrophobicity

The main-chain benzoxazine (BA-ddm) and diamine-type benzoxazine (Ph-hda) were prepared by solution method, and a series of copolymers were prepared by mixing them at various mass ratios. Second, copolymer coatings (P(PB)) were prepared on the surface of the tinplate by dip coating and heat curing. The results of FTIR and 1 HNMR showed that the benzoxazine copolymer coating was successfully prepared. DSC test results showed that the copolymerization of two benzoxazine oligomers was promoted by the introduction of BA-ddm containing phenolic hydroxyl groups. The introduction of Ph-hda containing a long aliphatic chain provided the copolymer coatings with good hydrophobicity, as verified by the hydrophilicity and hydrophobicity tests. When the mass ratio of BA-ddm to Ph-hda was 1:19, the water contact angle and water absorption of P(PB5) were 100.1 0 % and 0.56%, respectively. The results of dynamic polarization curves and electrochemical impedance spectroscopy (EIS) indicated that different copolymer coatings had good corrosion resistance. Among them, the P(PB5) coating exhibited the best anti-corrosion performance, with a corrosion current of 5.15 × 10 −8 A cm −2 , a protection efficiency of 99.23%, and an impedance modulus of 1.78 × 10 7 Ω cm 2 at 0.01 Hz, which was nearly 5 orders of magnitude higher than the impedance modulus of the blank tinplate.