Kinetics of diisocyanate reactions with chain-extending agents

The kinetics of polyurethane formation reactions was studied using the interaction of hexamethylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and tolylene 2,4-diisocyanate with the chain-extending-agents 1,3-and 1,4-butanediol as an example. For pair interactions of functional groups of diols with diisocyanates, rate constants were calculated. The effect of the nature of diisocyanates and the structure of diols on the kinetics of the reactions under consideration was examined. It was shown that, at the final stage of polyurethane formation, the reactivities of aromatic tolylene 2,4-diisocyanate and aliphatic hexamethylene diisocyanate level off. The influence of dibutyltin dilaurate as a catalyst on the reactivity of functional groups was assessed. It was established that the reactivities of functional groups of asymmetric molecules level off in the presence of the catalyst. It was demonstrated that the structure of diols affects the thermal behavior of polyurethane block copolymers.