A new method for a kinetic study of reactions between di-isocyanates and alcohols. Part 1. Symmetrical di-isocyanates

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Abstract
A new method of following the kinetics of the uncatalysed reaction between di-isocyanates and alcohols, which allows the determination of the concentration of all the species occurring during the reaction, by means of the high performance liquid chromatography (HPLC), is described. It has been found that the relationship between the unchanged fraction and the fraction that reacts, theoretically inferred for ideal systems (null catalytic effects), is validated over the whole reaction for real systems. This fact is a verification that the reduced time, τ, is a result of the total catalytic effects, and is a surprising simplification of the kinetics of this type of complex process. The following value ratios of the rate constants (R) for the first and the second NCO groups for various di-isocyanates were determined: 4,4′-BDI R= 1.36, 4,4′-BBDI R= 1.30, p-PDI R= 2.57, m-PDI R= 3.07.