CURING KINETICS OF POLYURETHANE REACTIONS

The curing reactions of polyurethane resins are accelerated by electron donors (e.g., hydroxyl group) and electron accepting materials (e.g., carboxyl group and dibutyltin dilaurate). As the critical extent of reaction is reached, a three‐dimensional cross‐linked network is formed. Afterwards, most of the reactive functional groups are attached to the cross‐linked network. The mobilities of these reactive functional groups are seriously restricted and the curing reactions become diffusion controlled. This could lead to incomplete extent of reaction. Based on elementary reaction mechanisms a kinetic model is developed. The concept of diffusion‐limited reactions is used to describe the phenomenon of limiting extent of reaction. Changes in free volume are related to changes in the rate constants with extent of reaction. When the model is applied to experimental data available in the literature, agreement between the model predictions and experimental data is reasonably good. Copyright © 1990 John Wiley & Sons, Inc.