Methylene diphenyl diisocyanate

A structural formula of 4,4'-MDI, one of the isomers of methylene diphenyl diisocyanate.

Methylene diphenyl diisocyanate, abbreviated as MDI, is an organic chemical compound used to make polyurethane, a type of plastic. MDI is the most important isocyanate in the chemical industry.

Types

The four different types of MDI as structural formulas.

There are four types of MDI: three positional isomers where the locations of the isocyanates change, and an oligomeric version where more than two rings are linked together, called polymeric MDI or pMDI. Different types of MDI make polyurethanes that have different properties. The 4,4' isomer, where the isocyanates are on the opposite side of the aromatic rings from the methylene bridge, is the most important.