How is polyurethane coating made from isocyanates and alcohols?

Polyurethane coatings are produced through the reaction of isocyanates—compounds containing the NCO functional group—with alcohols, which contain the OH functional group.1

In two-component coating systems, an isocyanate-terminated prepolymer is mixed with a polyfunctional alcohol (often referred to as a polyol) just prior to or during application. This reaction is typically facilitated by a catalyst, such as a tin soap, to ensure the coating cures rapidly within specific time and temperature requirements. As these components react, they form a three-dimensionally cross-linked network joined primarily by urethane groups, resulting in a high-performance, durable film.2314

While two-component systems are common, other formulations exist, such as one-pot systems where isocyanate groups react with atmospheric moisture or are thermally "blocked" until baked. Solvents are frequently added to these mixtures to manage viscosity as polymerization progresses. These versatile coatings are widely applied to materials including wood, concrete, and various machine parts.32