The effect of reaction conditions on the urethane prepolymer formation

Summary

In the two step synthesis of urethane copolymers, most statements from the literature assume that all of the diisocyanate will be used up in the formation of the isocyanate-endcapped polyol. However, a computerized simulation indicated the formation of three kinds of product.

Synthetic experiments were conducted to study the first step of this reaction. It was found that not all of the intermediates reacted in the first step of the synthesis. Some diisocyanate remained unreacted and a polyol dimer was formed. Two different polyols were used in this study. When a polyol has primary hydroxyl groups on each end, more unreacted diisocyanate was present at the completion of the reaction than when the polyol has a primary and a secondary hydroxy end. The investigation of the solvent effect revealed that the solvent used had little effect on the prepolymer formation. The study of the temperature effect showed that more unreacted diisocyanate was obtained at the higher temperature for the 4,4′-diphenylmethane diisocyanate/polytetramethylene glycol reaction.