The kinetics of the reaction of isophorone di-isocyanate with mono-alcohols

Isophorone di-isocyanate (IPDI) is used to react with hydroxyl containing prepolymers in the preparation of polyurethane elastomers, particularly with hydroxy-terminated polybutadiene (HTPB) in composite propellant systems. In the present work, the kinetics of the reaction of IPDI with monoalcohols are studied, as a model for the polyurethane systems. A gas chromatography method is used to follow the reaction, which allows direct measurement of the reaction of individual isocyanate groups. The rates of individual isocyanate groups are described by a second order equation modified to include catalysis by the urethane products. The rates of primary and secondary isocyanate groups in the two isomers of IPDI are compared. Differences between the various isocyanate groups are relatively small, and are offset by the urethane catalysis effect, so that the overall disappearance of isocyanate is roughly second order. The reaction rate of IPDI with HTPB is faster than with the model compounds, and it is suggested that this arises because there is tendency for the isocyanate to complex with the hydroxyl end groups of the polymer.