Polyurethane coatings have been around for decades and have a proven track record. Polyurethane as a class of technology was first invented by Otto Bayer in the late 1930's. The first use of polyurethane as a coating was in the 1940's, as an aromatic hardener-based coating. Aromatic hardeners posed a challenge in exposed applications due to the double bonds in the molecular structure that were susceptible to sunlight and broke down the bonds causing the material to yellow. The biggest issue with these broken bonds, particularly in the coatings industry, was that chromophores (color bodies) formed in the polymer matrix. For example, when the sun hit a blue pigmented, aromatic-based polyurethane coating and the polymer matrix turned yellow over time, this added yellow color to the blue hue, eventually giving the coating the appearance of being green. Or, if an aromatic hardener-based coating was used as a clear coat on top of gray concrete, the concrete surface turned beige as the coating yellowed over time.
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