ABSTRACT
Prepolymers are formed by the reaction of an excess of diisocyanate with a polyol. One of the isocyanate groups (NCO) reacts with a hydroxyl group (OH) of the polyol. Another isocyanate group reacts with the second OH group. A very important feature of this reaction is that there are no by-products formed. The resultant product has isocyanate groups on both ends with urethane bonds between the original polyurethane and the diisocyanate group. Figure 3.1 shows the basic reaction.
