Isocyanates are the compounds that react with alcohol-based compounds to form polyurethane polymers. These products are defined by the number of -NCO groups that they contain, and most of them are in a liquid state at room temperature. Isocyanates are very reactive and have a low molecular weight. They are used in industries from the automotive sector to construction, where polyurethane manufacturing is performed. Generally, two types of isocyanate content are used in forming polyurethane foam structures. These are polymeric MDI in rigid polyurethane foams, and monomeric MDI in sponge foams.
Polymeric MDI (PMDI)
Polymeric MDI, also know as oligomeric MDI, is used as an isocyanate compound in rigid polyurethane foams. The mean functionality is between 2.2 and 3.0. The chemical notation is as follows.
Dark brown in color, it is a liquid isocyanate structure in aromatic form, known as Polymethylene Polyphenylisocyanate. It has a density of 1.22, and is present in the range of 200-800 cP viscosity. % NCO content is in the range of 30-31.5. 90% PMDI use is present to form a rigid polyurethane foam structure.
Monomeric MDI is a solid, and is white or light yellow in appearance. It is also known as 1.1′-Methylenebis (4-isocyonatobenzene), 4.4′-Methylene diphenyl diisocyanate and pure MDI. Its chemical formula is C15H10N2O2. It has a melting point of 40°C and a boiling point of 314°C. Its molecular weight is 250.25 g/mol. Its structure is completely 4.4 MDI. It is the main isocyanate compound used in polyurethane formation.
Monomeric MDI is a liquid which is colorless or light yellow in appearance. Modified MDI has a density of 1.20 (25C). It is present in the range of 200-800 cP viscosity. Its NCO% content is 33.40’. It is the main isocyanate compound used in polyurethane formation.