Methylene diphenyl diisocyanate, most commonly known as MDI, is an aromatic diisocyanate, which exists in three isomers, 2,2-MDI, 2,4-MDI, and 4,4-MDI. The 4,4 isomer, also known as pure MDI, is most widely used. MDI reacts with polyols in the formulation of polyurethane foams. The major application of 4,4-MDI is the production of rigid polyurethane foams.
Available grades are mentioned below: