In-situ monitoring of urethane formation by FTIR and Raman spectroscopy

Reactions of 2-propanol, 2-butanol, 2-pentanol, 2-hexanol, and 2-octanol with phenylisocyanate were monitored by FTIR and Raman spectroscopy. The results show that Raman spectroscopy is as effective as FTIR spectroscopy in following urethane reaction kinetics. The activation energies calculated are 10.0, 10.5, 11.9, 12.8, and 14.8 (kcal/mole) for 2-propanol, 2-butanol, 2-pentanol, 2-hexanol, and 2-octanol reacting with phenylisocyanate without catalyst, respectively. The steric hindrance effects of primary, secondary, and tertiary butanol with phenylisocyanate reaction kinetics were observed. The initial reaction rates of these alcohol systems have a typical ratio of 1:0.3:0.1, respectively. The reaction kinetics simulation, based on a simple kinetics model, fits reasonably well with experimental data obtained by Raman spectroscopy. This agreement further demonstrates the effectiveness of Raman spectroscopy in monitoring urethane reaction kinetics and suggests an effective method for verifying the reaction kinetics and mechanism under nonisothermal conditions. The results of this work will form the basis for our future in-situ study of thermoset polymerization kinetics under exposure to radio frequency electromagnetic (RF) fields.