Infrared Spectroscopic Determination of Unreacted Isocyanates in Polyurethane Films

A simple and quick method has been developed for the quantitative determination of unreacted isocyanates remaining in polyurethane films. A modified Siggia-Hanna method was applied to stripped polyurethane film flakes. The film flakes were treated with anhydrous dioxane solution of n-butylamine at 20 t, the reaction time required being from 2 to 20 hrs. depending on the polyurethane film thickness of 10 to 50 microns. The values obtained with this method were plotted against the ratios of absorbance at 2,260 cm-1 to that at 2,950 cm-1. For the determination of absorbance ratio the attenuated total reflection method was employed directly on coated polyurethane films. The advantages of this analytical method are that it can be applied to pigmented films and also to kinetic studies.