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Diisocyanates and polyisocyanates are reactive intermediates characterized by terminal isocyanate groups (–N=C=O), which typically are reacted with the hydroxyl groups of polyol coreactants to form polyurethanes.
The most widely used diisocyanates and polyisocyanates are aromatic in their composition. A product mixture of polymethylene polyphenylene isocyanate (also called polymeric MDI or PMDI) and p,p'-methylene diphenyl diisocyanate (MDI) is derived from aniline (via benzene). Toluene diisocyanate (TDI, or tolylene diisocyanate) is derived from toluene.
Active worldwide trade takes place in diisocyanates and polyisocyanates—TDI in its various isomer mixtures (the bulk form is the 80:20 isomer mixture), MDI in various forms (the bulk form is “polymeric” MDI in the functionality range of 2.3–3.0) and also the lower-volume specialty products of the aliphatic and cycloaliphatic type. Substantial exports of TDI and MDI go to regions such as Asia Pacific countries, South America and Eastern Europe, as production of isocyanates in these areas is minimal. World consumption of diisocyanates and polyisocyanates was approximately 5.2 million metric tons in 2004.
Future growth of MDI is expected to be up to twice that of GDP growth, while TDI growth will approximate GDP growth. As domestic demand for MDI and TDI has slowed in recent years, some of the major producers have shut down older facilities (sometimes in conjunction with new plant capacity) and increased export volumes to the faster-growing regions of the world such as Asia Pacific, South America and Asia. In addition, most major producers have a worldwide presence—production facilities and/or joint ventures in North America, Western Europe, Japan and other regions of the world.
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