POLYURETHANE COATING CHEMISTRY
The chemistry of the Isocyanate group (-N=C=O) forms the basic foundation of polyurethane coatings chemical chemistry. Its superior chemical Reactivity and its ability to interact with a wide range of chemical partners make the isocyanate group ideal for the market for coatings. The isocyanate group reacts with any substance that contains oxidizing hydrogen, such as alcohol (R-OH) as well as an amine (R-NH2) or also water (H2O). There are many kinds of amine and hydroxyl-containing raw materials (often known as polyols or co-reactants) that can react with isocyanate-containing raw materials. The three chemical reactions (shown in Schemes 3 and 4) are particularly important.
OCN-R’-NCO + HO-R-OH -(R-O-C(O)-NH-R’)n1.
Polyurethane H2N-R-NH2 + NCO-OCN-R’-N -(R-NH-C(O)-NH-R’)n2
Polyurea R-NCO + H2O [RC(O)OH R-NH2 + CO2 3
Two-component polyurethane coatings, also known as two-package coatings, are the most widely known polyurethane coatings. Two-component is a term used to describe a process where two different resin packages (often known as Part A and part B) are blended immediately before application. One package has resins that react with chemical groups (e.g., alcohols, hydroxyl, or amines), and the second has a polyisocyanate resin capable of reactivity with chemical groups. The main benefit that comes with the double-component coating is its theoretically unlimited storage stability coupled with the speedy curing reactions once they are combined.