Reaction kinetics of toluene diisocynate and propanol by in situ FTIR

Purpose - To evaluate the effect of the concentrations of isocyanate group and hydroxyl group and hydroxyl group species on the rate constants of isocyanate-propanol reaction, and to reveal the kinetics of isocyanate-hydroxyl reaction. Design/methodology/approach - The in situ FTIR technique was employed to measure the group concentration evolutions, by which the rate constants were determined. Besides, the FTIR was used to detect the OH absorbance shifts during reaction and the OH absorbance at different concentrations. The kinetic mechanism of isocyanate-propanol reaction was discussed with the combination of rate constants and FTIR spectra. Findings - A new reaction mechanism, alcohol association mechanism, was proposed that could explain many phenomena. It was revealed that the rate constant was independent of the isocyanate concentration, while the concentration and species of hydroxyl groups had apparent effects on the rate constants. It was possible to calculate the number averaged degree of association of propanol with alcohol association mechanism. Research limitations/implications - The associated n-propanol molecules that reacted with isocyanate to form urethane were the associated dinner and trimer predominately, while the iso-propanol was the dimer. Practical implications - The kinetics of isocyanate-hydroxyl reaction and the alcohol association mechanism will be helpful to understand the preparation and curing of polyurethane, and their controls. Originality/value - A new reaction mechanism, alcohol association mechanism, was proposed that could explain many phenomena that might not be interpreted by other mechanisms. The mechanism could be employed to calculate the number averaged degree of association of alcohols.