Primary Hydroxyl Content of Soybean Polyols

Polyurethanes are obtained by reacting polyols with polyisocyanates. The primary hydroxyl content is a very important characteristic of polyols because it affects their reactivity. Typically primary hydroxyls are approximately threefold more reactive than the secondary hydroxyls when reacting with aromatic isocyanates. This paper presents a simple and convenient kinetic method for determining the primary hydroxyl content in soybean polyols, based on the difference in reactivity of primary and secondary hydroxyls with phenyl isocyanate (PI). The reaction kinetics were studied by following the disappearance of the NCO band at 2260 cm−1 with time in the infrared spectra. The reaction of PI with soybean polyols was carried out in a toluene:dimethylformamide (9:1, v/v) mixture. The relative error of the method is in the range of ±5%. The method is characterized by simplicity and good reproducibility, and it can be applied to all soybean polyols irrespective of their structure.