polyisocyanaten

Polyisocyanates are a class of organic compounds that contain two or more isocyanate (-NCO) groups per molecule. They are the key reactive monomers used to produce polyurethanes, forming urethane linkages when they react with compounds containing active hydrogen such as polyols or amines. The resulting polymers range from foams to coatings and elastomers.

Commercially important diisocyanates include toluene diisocyanate (TDI), methylene diphenyl diisocyanate (MDI), and hexamethylene diisocyanate (HDI). In many applications, these diisocyanates are used in polymeric or crude forms (polymeric MDI, PMDI) with higher functionality and different reactivity. Polyisocyanates may be used directly, or converted into prepolymers or quasi-prepolymers that contain active NCO groups for subsequent reaction with polyols.

Production is typically achieved by methods that convert precursor amines or urethane intermediates to isocyanates, often via phosgene routes or modern non-phosgene processes. The resulting materials are handled under controlled conditions to minimize exposure, as residual moisture can react with isocyanates to produce carbon dioxide and amines, leading to pressure build-up and corrosion of materials.

Applications include flexible and rigid polyurethane foams for furniture and insulation, coatings for wood and metal, elastomeric parts, sealants, adhesives, and composite materials. The reactivity of isocyanate groups with polyols and other nucleophiles enables a wide range of formulations and properties.

Health and environmental aspects are important due to the potential of isocyanates to cause respiratory sensitization and irritation. Workers may be exposed during manufacturing, handling, or application; appropriate engineering controls, ventilation, personal protective equipment, and monitoring are required. Regulations require labeling, exposure limits, and safety data sheets.