Polyurethanes have been around for nearly 90 years after their discovery by Otto Bayer in the mid-1930s. Some of that first work was done with aromatic isocyanates (hardeners) reacted with hydroxyl-functional resins to create rigid foams. Within a decade, in the 1940s, there were the first demonstrated uses of aromatic hardeners in creating polyurethane-based coatings. It took another 20 years for the development of aliphatic hardeners and their incorporation into light-stable polyurethane coatings in the 1960s. The ‘70s saw the introduction of waterborne polyurethane dispersions (PUDs) as well as the advent of both two-component (2K) solventborne and solvent-free polyurethane coatings. In the 1980s, we saw the first use of tough 2K-thick-film polyurea coatings, promulgated by the discoveries and developments of Dudley Primeaux, unofficial father of spray-polyurea coatings. Around that same time, a new class of resins, polyaspartics, were invented by Covestro, LLC that extended the portfolio and use of polyurea coatings into thin-film applications. Around this same time, the first generation of lower-VOC, 2K-waterborne-polyurethane coatings hit the market with limited success. About 20 years later in the early 2000s, the second generation of 2K waterborne coatings were released with major improvements in hardness, chemical resistance, and reductions in VOC. Finally in the 2010s, the second generation of polyaspartic resins were developed, targeting lower viscosities for reduced VOCs, as well as the ability to formulate more flexible versions of this typically high-hardness coating.
In this article we will review several reasons for the excellent physical properties of polyurethanes and polyureas, as well as how these reasons differ between the two chemistries. Then we will explore many of the common terms used to describe both technologies based on resin type, hardener type, carrier, and number of components. The often-confusing naming conventions will be simplified by comparing the classes and sub-classes to our canine compatriots. This will be followed by a technology review and benefit/drawback analysis of several of the sub-coating classes, including conventional thin-film coatings as well as 100% solids, thick-film coatings. We will conclude with real-world case studies where these versatile coatings have proven long-term performance.