Metylenodifenylodiizocyjanian

Metylenodifenylodiizocyjanian, known in English as methylenediphenyl diisocyanate (MDI), is a family of aromatic diisocyanates that serves as a key building block in polyurethane chemistry. The molecule consists of two phenyl rings connected by a methylene bridge and bearing an isocyanate group (-NCO) at reactive positions on each ring. Commercial MDI products are complex mixtures of several structural isomers, with the 4,4'-isomer typically the main component, accompanied by 2,4'- and 2,2'-isomers.

Production typically involves condensation of aniline with formaldehyde to give methylenediphenyl diamine (MDA), followed by phosgenation to form the diisocyanate. The process may also employ phosgene-free routes. The results are sold as crude or partially purified MDI blends and are often handled as prepolymers or polyol blends in polyurethane production.

Primary uses: the diisocyanate functionality enables crosslinking with polyols to form polyurethanes. MDI-based formulations are used to produce rigid polyurethane foams for insulation, flexible foams for furniture and automotive seating, coatings, adhesives, sealants, and elastomeric products. The 4,4'-MDI content influences properties such as rigidity, hardness, and thermal stability of the final polymer.

Safety and environmental aspects: MDI is an irritant and a respiratory sensitizer; exposure can cause asthma and dermatitis. Handling requires appropriate engineering controls, personal protective equipment, and monitoring. MDI reacts with water forming polyurea and carbon dioxide; storage and transport must prevent moisture ingress and unwanted polymerization. Environmental concerns include toxicity to aquatic life and potential air and soil exposure; regulatory frameworks govern labeling, handling, and spill response.