A novel benzoxazine (BA-BZ-COOH) monomer has been prepared and its structure has been proved using various measurements. PBA-BZ-COOH/nanocomposites reinforced with varying content of modified nanoclay (MNC) have been prepared in situ polymerization method for superior thermal, optical, and anti-corrosion properties. The resulting nanocomposites are showed a good dispersion of MNC in the PBA-BZ-COOH matrix without aggregates and a partial intercalated/exfoliated structure. The PBA-BZ-COOH/MNC (3%) composite that cured at 210 °C had high glass transition temperature (190 °C), and high UV shielding (97 and 85% at wavelength 275 and 375 nm, respectively). Finally, PBZs nanocomposites with varying contents of MNC (0.5, 1, 2, and 3%) were prepared as coatings on MS and their anti-corrosion performance were discussed in detail. The electrochemical results showed …