Chemical Reactions of the Isocyanates

These reactions can be divided into two categories. They are additions to compounds with active hydrogens and self-condensation. The reactions are well described in organic chemistry textbooks, so there is little reason to describe them here. It is noteworthy, though, that the uncatalyzed reactions of isocyanates with various active hydrogen compounds are probably broadly similar. Among them, the most investigated reactions are the ones of alcohols with isocyanates [123]  

Electron withdrawing substituents increase the positive charge on the isocyanate carbon and move the negative charge further away from the site for the reaction  

This makes an attack by an electrOTi donor easier and yields a faster reaction. Electron donating groups, therefore, have an opposite effect. 

Catalyst Relative rates of reactioiis with -butyl aleohol 

---

Most investigators agree that the strength and durability of isocyanate-bound wood panels are due to the chemical reaction of the isocyanate group with wood hydroxyls as illustrated by the above equation. Thus, the multifunctional isocyanate molecule forms a chemically bonded bridge between two or more adjacent wood particles. This reaction is only one of several involving isocyanates that can and probably do occur in a hot press during formation of particleboards when isocyanate binder is used. A very important reaction is that of isocyanate with water to produce a very unstable carbamic acid which immediately decomposes to form a primary amine and COg ... 

The chemistry of polyurethane foam formation is complex and has been reported elsewhere . A more simple treatment is given below. Polyurethane foam formation is dependent upon the chemical reactions of the isocyanate group — N C O. 

---