Methylendiisokyanaatteja

Methylendiisokyanaatteja, known in English as methylene diphenyl diisocyanates (MDI), are a family of aromatic diisocyanates that serve as key monomers in polyurethane production. They consist of two isocyanate groups (-NCO) attached to a methylene-bridged diphenyl unit. Commercially, the term encompasses several isomeric forms, including the 4,4'- and the 2,4'- and 2,2'- isomers, as well as polymeric MDI (PMDI), a higher molecular weight mixture used in various polyurethane formulations.

Chemical and physical properties vary by grade but generally MDI components are reactive liquids or solids at room temperature. They readily react with polyols to form polyurethanes and can hydrolyze in the presence of moisture to amines and carbon dioxide. Due to their reactivity, MDIs are typically handled under controlled conditions to prevent premature polymerization and exposure.

Production and handling: MDIs are produced primarily by phosgenation of methylenediphenyl diamines or related intermediates. They are stored and transported under controlled conditions to minimize emissions and avoid degradation. Special equipment and containment are standard in manufacturing and processing facilities.

Applications: The most significant use of MDIs is in polyurethane foams, both rigid and flexible, used in insulation, furniture, bedding, and automotive interiors. They also find use in coatings, elastomers, adhesives, and sealants.

Safety and regulatory considerations: Isocyanates are common occupational sensitizers and can cause irritation and asthma with exposure. Handling requires adequate ventilation, personal protective equipment, and adherence to occupational exposure limits. MDIs are regulated in many regions under chemical safety and environmental frameworks.

See also: polyurethane chemistry, isocyanates, PMDI.