Polyurethanes are made from the reaction of diisocyanates with polyols. The network is comprised of a soft segment that contributes to elasticity, resilience and low temperature performance (polyol) and a hard segment that can impart hardness and flexural strength (NCO-extender).
Common diisocyanates used include TDI, MDI (also in polymeric form), HDI, and IPDI. Typical polyol types used include polyesters, polyethers, polycarbonates, polycaprolactones, amine terminated, and acrylics. Bio-based polyols, also referred to as Natural Oil Polyols (NOP), are also widely employed and can be derived from Cashew Nutshell Liquid (non-food chain), and various vegetable oils such soy bean, castor and palm oils, or sugars/starch.
A variety of additives such as catalysts, surfactants, moisture scavengers, diluents, flame retardants, chain extenders, pigments and fillers are used to control application behavior and performance.
In general, polyurethanes provide excellent weatherability, mechanical properties, adhesion to various substrates and abrasion and tear resistance amongst many valuable performance properties.