Polyurethanes make tough, durable adhesives, and adding polyurethane functionality to other adhesives is a great way to tailor their properties. The isocyanate monomers used to produce them can sometimes be too reactive, so blocked isocyanates offer an alternative. With the reactive isocyanate groups being unmasked at elevated temperatures, these chemicals can be useful for very different products than traditional polyurethanes. Polyurethanes make tough, durable adhesives, and adding polyurethane functionality to other adhesives is a great way to tailor their properties. This is thanks largely to monomer and prepolymer chemicals used in polyurethane preparation that contain isocyanate groups. Isocyanates are highly reactive, meaning that they can cure rapidly and that the bonds produced are strong. However, sometimes they can be too reactive. That reactivity makes isocyanates toxic, so it's important for adhesive makers to limit users' exposure to these chemicals. Also, sometimes a formulator doesn't want an adhesive to react quite so rapidly1.