Effect of temperature conditions on the mechanism of formation, molecular structure, and properties of polyurethanes

Abstract

AbstractThe formalized kinetic approach to the mechanism of urethane formation in the system of prepolymer with end NCO groups–1,4‐butanediol together with the dispersion analysis of kinetic curves have helped to establish that, at moderate temperatures, the mechanism may be represented by a scheme comprising a noncatalytic stage of urethane formation and a catalytic one including the formation of a double complex of a catalyst with an isocyanate or a hydroxyl group. As the temperature rises the proportion of the noncatalytic stage decreases significantly, while a mechanism, including the formation of the triple complex isocyanate group–catalyst–hydroxyl, becomes the most probable. It has been shown that the formation of a triple complex at elevated temperatures is thermodynamically more advantageous than the formation of double complexes; hence these changes of mechanism with temperature. It has been found that the temperature conditions of polyurethane production greatly affect the degree of its branching. Two crosslinked polyurethanes were obtained, one under the temperature conditions providing for the minimum degree of branching, the other under isothermal conditions. It has been discovered that the degree of branching of a prepolymer may greatly affect the density of chemical and physical bonds and a range of physical and chemical properties of the polyurethane.