Isocyanates
Isocyanates are an important class of monomers that readily react with compounds containing active hydrogen atoms, like amines, alcohols, water, and carboxylic acids. They can also be homo-polymerized to polyisocyanates (N-substituted 1-nylons).
The most important class of isocyante polymers are polyurethanes which are formed from the reaction of a diisocyanate with a polyol which leads to urethane linkages in the polymer backbone (-NH-C(=O)-O-).
Depending on the nature and functionality of the polyol and polyisocyanate, polyurethanes are either soft elastomeric materials or hard and rigid plastics.
The most important commercial isocyanates are diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI) and their polymeric forms. MDI and TDI are cheaper and more reactive than aliphatic isocyanates (HDI) whereas aliphatic isocyanates yield polymers that are more UV-stable (do not discolor) and are less susceptible to oxidation and degradation.
Applications
Isocyanates are a family of highly reactive, low molecular weight chemicals. They are widely used in the manufacture of flexible and rigid foams, fibers, coatings such as paints and varnishes, and elastomers, and are increasingly used in the automobile industry, autobody repair, and building insulation materials. Spray-on polyurethane products containing isocyanates have been developed for a wide range of retail, commercial, and industrial uses to protect cement, wood, fiberglass, steel and aluminum, including protective coatings for truck beds, trailers, boats, foundations, and decks.
