Phosphate-Functional Waterborne Acrylic Coatings for Superior Corrosion Protection and Surface Durability

The development of eco-friendly, solvent-free, and low-VOC coatings is essential for achieving sustainable protection of metallic surfaces. In this study, a phosphate-functional acrylate monomer, phosphated methacrylate (PMA), was synthesized through an epoxy ring-opening reaction between glycidyl methacrylate (GMA) and phosphoric acid without the use of any external catalyst. The resulting PMA was incorporated into a waterborne acrylic system via mini-emulsion polymerization to produce highly stable phosphated acrylic emulsions (PAE) with a solid content of 38–40 wt % and uniform particle sizes of 125–161 nm (PDI < 0.02). The emulsions showed excellent colloidal stability for over 180 days with a high zeta potential (−52 mV), confirming strong electrostatic stabilization. Structural and morphological analyses using FTIR, NMR, and SEM-EDS confirmed the successful incorporation and homogeneous distribution of phosphate groups within the polymer network. The resulting coatings demonstrated improved thermal stability, with degradation temperatures increasing from 396 °C for the pure acrylic to 416 °C for the 2.5 wt % PMA film. Mechanical testing revealed an increase in surface hardness (up to 4H) and a 2.6-fold improvement in adhesion strength, attributed to enhanced interfacial bonding and restricted polymer chain mobility resulting from the phosphate functionalities. Electrochemical studies, including EIS and potentiodynamic polarization, revealed exceptional anticorrosive performance of the 1.0 wt % PAE coating, characterized by a very low corrosion current density (Icorr = 3.5 × 10–11 A), high charge transfer resistance (Rct = 2.25 × 108 Ω), and a low corrosion rate (4.1 × 10–7 mmpy). These results demonstrate that PMA effectively enhances both adhesion and corrosion protection, providing a scalable, sustainable route to high-performance phosphate-functional waterborne acrylic coatings for long-term industrial applications.