Association of hydroxyl groups of oligomers and kinetics of polyurethane formation

The kinetics of the tolylene 2,4-diisocyanate reaction with α,ω-hydroxyoligobutadienes and polyoxypropylene glycols of different molecular masses were studied. Changes of the apparent reaction rate constants for consecutive steps of the urethane formation and their ratios on the total initial concentration of hydroxyl groups of oligomers were obtained. These dependences were shown to be determined by the presence of different forms of associated hydroxyl groups during the reaction. The parameter β was correlated with the concentrations of self-associates of hydroxyl groups of different types responsible for a change in the reactivity of both classes of oligomers. The urethane formation process was mathematically simulated and quantitative data on changes in the concentration of all hydroxyl-group associate types in the course of the reactions and their reactivity, which could not be directly measured experimentally, were obtained. The character of equilibrium between the associate types was shown to be determined by the proton-acceptor ability of oligomer-chain atomic groups involved in hydrogen bonding.