Multifunctional nitrogen rich benzoxazines with imine moiety: Structural insights, hydrophobic and corrosion‐resistant applications

Abstract

Hybrid hydroxynaphthaldehyde (HNA) based benzoxazine products with good thermal stability, anticorrosion and hydrophobic properties have been synthesized. Nitrogen rich Schiff base core bifunctional benzoxazines (HNAG‐f and HNBG‐f) and trifunctional benzoxazine (HNMA‐f) have been synthesized using amino‐derivatives and paraformaldehyde through Mannich condensation. The structural confirmation of benzoxazines was studied using ATR‐FTIR, HRMS and 1H‐NMR spectral analyses. The polymerization (curing) temperature and thermal stability were assessed by DSC and TGA respectively. Data from DSC and TGA studies infer that HNMA‐f possesses the lowest curing temperature of 213°C and the highest thermal stability with a char yield of 41% at 850°C respectively when compared to those of the polybenzoxazines synthesized. The values of LOI and HRI calculated using TGA data infer that all the polybenzoxazines can be used for self‐extinguishing, flame retardant and heat resistant applications. Corrosion results indicated that these benzoxazines exhibit the surface protection efficiency of 99% towards mild steel surfaces. The polybenzoxazines exhibited hydrophobic property with a water contact angle value (WCA) of above 140°. The value of WCA did not vary much on exposing the polybenzoxazine coating to chemical and UV treatments suggesting that the polybenzoxazine coatings are durable. Data from different studies infer that these benzoxazines can be used in the form of adhesives, coatings, and thermally stable, anticorrosive, and hydrophobic and UV resistant applications.