ABSTRACT
The common feature of all polyisocyanates is the presence of more than one N=C=O group. Diisocyanate monomers (Fig. 18.1), the forerunners of all polyisocyanates, were first discovered in the late 1840s by Wurtz (4). One prototype, toluene diisocyanate (TDI) was developed by I.G. Farben in Germany during World War II for the manufacture of polyurethane, while another, hexamethylene diisocyanate (HDI), was developed by H. Reinke to create a melt spinnable fiber that would circumvent DuPont’s nylon patents (2,4). A number of related compounds have subsequently been developed and utilized commercially, with methylene diphenyl diisocyanate (MDI), naphthalene diisocyanate (NDI), and isophorone diisocyanate (IPDI) being the other major diisocyanates. Diisocyanate dimers, trimers, and polymers based on HDI and MDI are being used more commonly (Fig. 18.2). Although these polyisocyanates have inherently lower vapor pressures and volatility in comparison with their corresponding diisocyanate, they can still cause diisocyanate asthma (DA).
