Isocyanates in polyaddition processes. Structure and reaction mechanisms

The multiple possible addition processes of isocyanates, in accordance with a new proposed general classification based on the interatomic bond type changes is presented. Starting from the latest achievement of the physicochemical methods, new aspects regarding the isocyanates structure and different hydroxy compound association forms as part of the addition processes were revealed. Some basic reaction mechanisms presented in the current: research were re-evaluated in accord with recent quantum chemical and kinetic data. The intramolecular hydrogen bonding in the symmetrical diols was found to determine a significant difference between their two -OH group reactivities. Recent kinetic and other reactivity measurements, extended to polyfunctional systems reported in some macromolecular synthesis, were presented. The perspective of these findings, in order to obtain in the near future an acceptable mathematical model of the polyaddition process by involving the multiple new synergetic effects observed in different real complex reaction mixtures, is analysed. (C) 2001 Elsevier Science Ltd. All rights reserved.