Quantitative Determination of Small Amounts of Toluene Diisocyanate Monomer in Urethane Adhesives by Gel Permeation Chromatography

Existing quantitative methods for determining isocyanate monomers are either too insensitive for small quantities, tedious, or give partially erroneous results due to sample reaction with moisture in the reagents or decomposition of sample where elevated temperatures are employed in the analysis. The objective was to develop a basic quantitative method which, with a minimum of modification, could be adapted to a variety of polyurethane products for quality control. Before chromatographing, the sample is treated with specially dried ethanol to convert the free monomer and any isocyanate groups on the prepolymer chain to the respective urethane derivatives. The sample is then diluted with tetrahydrofuran and chromatographed at room temperature on a 200, 200, 100, 100, 60 angstrom column series using a differential refractive index detector. Essentially, the basic procedure is not new or unique but its conversion to a quantitative reproducible method represents a breakthrough as far as a practical approach is concerned.