Diisocyanate Chemistry Lab Report

In 1937, the German scientist “prof. Otto Bayer” and his co-workers was find out the poly addition reactions1-4 where the polyaddition of diols and diisocyanates in the presence of catalyst to proceeds completely to forms a polyurethanes (PUs) in the presence of mild conditions to avoid the undesired by products. Hence, prof. Otto Bayer was recognized as a “father” of polyurethanes. At the time of during World War II, for aircraft coating purpose in small-scale PUs was used but that time polyisocyanates not available in market. After that the World War II, some research groups focused on their activities and interests in PUs establishment in various countries like U.S.A and U.K but the commercial development is very slow. However, the German

Because of limitless industrial importance of PUs, hence need to study diisocyanate chemistry briefly and understand the properties and their reactivity. Mainly the isocynates are highly reactive and allow to forming urethane groups without any by-products formation. This isocyanates contains two or more –NCO functional groups for one molecule is called as diisocyanes or polyisocyanate respectively. The industrial important monoisocyanate compound is methyl isocyanate (MIC), majorly used to manufacturing of pesticides but this isocyanate is extremely hazardous which is responsible to Bhopal disaster, in 1984. All diisocyanate are liquids or solids in the nature and highly reactive, it undergo reaction across the double bond C=N of the –NCO group. The reactivity of the isocyanates are mainly depends on the electron density of the central carbon atom of the isocyanate, the low electron density of central carbon atom contains compounds are highly reactive means the aromatic diisocyanates are highly reactive than aliphatic because of resonance structures. Therefore, the electrophilic nature of the aromatic diisocyanates can alter through different substituents on aromatic ring like electron withdrawing or donating groups. The reactivity of diisocyanates plays important role to synthesis of polyurethanes because the possibility to form dimers, trimmers and higher oligomers and also possible to form polymers. In addition, the number of cross-linking reactions may be take place, mainly depends on the reaction conditions such as temperature, catalysts, the structure of the alcohols, amines and isocyanates. Commonly used some isocyanates structures are shown in figure 1.2 that is toluenediisocyanate (TDI),