A benzoxazine/substituted borazine composite coating: A new resin for improving the corrosion resistance of the pristine benzoxazine coating applied on aluminum

In this paper, laboratory synthesized Phenol-paraPhenyleneDiAmine (P-pPDA) benzoxazine containing different amounts of B-trimesityl-N-triphenylborazine was applied by spin coating on aluminum and thermally cured. The addition of the borazine derivative (borazine 1) does not appear to modify the curing characteristics of the P-pPDA matrix itself as shown by FTIR, DSC and DEA analyses; however, some interactions - chemical and/or physical (co-crystallization) - between P-pPDA and borazine 1 cannot be excluded. The microstructure of the composites is characterized by a two phase system consisting of a dispersion of nanosized (10-20 nm) clusters for the lowest borazine 1 concentration (0.5 wt%), evolving towards bigger (100-200 nm), agglomerated clusters for higher borazine 1 concentrations (3 wt%) and finally, continuous, dendritic structures within the P-pPDA matrix for the highest borazine 1 concentration (10 wt%). The benzoxazine composite coating containing 0.5 wt % trimesitylborazine derivative showed a largely increased and durable ability to protect the aluminum substrate. It is shown that a highly capacitive behavior and durable barrier properties can be obtained for P-pPDA coatings containing such a low amount of borazine derivative homogeneously dispersed in the benzoxazine matrix. For concentrations of 3 wt%, as agglomeration took place and dendrites appeared for the highest concentration of borazine derivative (10 wt%), the corrosion resistance decreased with time.