Synthesis and Characterization of a Transparent Siloxane- co -Polyurethane Anti-Corrosion Coating for a Copper Substrate

Abstract

Corrosion on copper usually happens slowly and forms a protective layer. However, factors like low pH, high oxygen, or contaminants such as chlorine and ammonia can speed up this process, causing serious problems. This is especially common in plumbing, industrial heat exchangers, and electrical systems. In this study, we developed a siloxane-co-polyurethane (Si-co-PU) random copolymer coating aimed at preventing corrosion on copper. The copolymer was synthesized through the step-growth polymerization of three comonomers: isophorone diisocyanate, hexanetriol, and hydroxyl-terminated oligomers of polydimethylsiloxane (PDMS). The formation of the random copolymer was confirmed using various characterization techniques, including ATR-IR, NMR, XPS, XRD, etc. The polymerization reaction was stopped very quickly to recover liquid prepolymer for coating application, followed by subsequent curing in an oven to form a cross-linked copolymer network on the copper substrate. The resulting coating is amorphous and displays glass-like transparency. We varied the thickness and curing temperature of the coating to optimize its performance. The Electrochemical Impedance Spectroscopy (EIS) study revealed that the coating with a concentration of 20 mg/mL and a thickness of 96.26 μm, cured at 60 °C, displayed the best anticorrosion properties. Specifically, this pristine coating demonstrated remarkable corrosion resistance when immersed in a 3.5 wt % NaCl solution. Initially, the low-frequency impedance (|Z|0.01 Hz) measured approximately 107 Ω·cm2. Notably, even after 7 days of exposure, the impedance remained significantly high, around 105 Ω·cm2, indicating sustained protective performance. To evaluate the long-term stability of the coating, an accelerated corrosion test was conducted using a highly corrosive electrolyte solution of 6 wt % FeCl3 in 0.1 M HCl. A minute mass loss over 24 h immersion in the corrosive electrolyte demonstrated the excellent barrier property. Additionally, the coating demonstrated strong adhesion to both metal and glass substrates, as confirmed by the cross-cut adhesion test.