1.1 ,This test method determines the ratio of the infrared absorbance of uretidinedione (dimer) in methylene-4,4’,- di(phenylisocyanate) to an infrared absorbance at a reference wavelength within the same material. It is applicable to monomeric methylene-di(phenylisocyanate), or “,Pure MDI,”, containing 95 ,% or greater methylene-4,4’,-di(phenylisocyanate).