Hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene as an Environmentally Friendly Modifier for Polyurethane Powder Coatings with Increased Thermal Stability and Corrosion Resistance.

Protection against fire and the corrosion of metals is necessary to ensure human safety. Most of the fire and corrosion inhibitors do not meet the ecological requirements. Therefore, effective and ecological methods of protecting metals are currently a challenge for researchers. In this work, the influence of hexakis(4-(hydroxymethyl)phenoxy)cyclotriphosphazene (HHPCP) on the characteristics of powder coatings was examined. The coatings' properties were investigated by measuring the roughness, hardness, adhesion to the steel surface, cupping, gloss, scratch resistance, and water contact angle. The thermal stability was studied by furnace test and TGA analysis. The corrosion resistance test was carried out in a 3.5% NaCl solution. The distribution of phosphazene-derived segments in the coating was examined by GD-EOS analysis. Modified coatings show better corrosion and thermal resistance and can be used for the protection of the steel surface. Their better corrosion resistance is due to the electroactive properties of the phosphazene ring and its higher concentration at the coating surface, confirmed by GD-EOS analysis. The increase in thermal resistance is due to the effect of the formation of phosphoric metaphosphoric and polyphosphoric acids during the decomposition of HHCPC, which remain in the condensed char phase and play a crucial role in surface protection.