ADSORPTION OF METHYLENE DIPHENYL DIISOCYANATE (MDI) ISOMERS ON NATIVE ALUMINUM

摘要

In situ FTIR-ERA spectroscopy shows that the adsorbed MDI isomers (i.e. 4,4'-MDI, 2,4'-MDI, 2,2'-MDI) undergo notable changes of their vibrational state on the native surface of Al. Once the MDI molecules are brought into contact with the metal surface, different adsorption states are observed. The amount of adsorbed material varies with the isomer. During the MDI adsorption, a considerable amount of only physically interacting molecules is deposited on top of a chemically adsorbed layer of 4,4'-MDI and 2,4'-MDI molecules. The weakly bonded molecules are washed away by ongoing THF rinsing. ERA spectra of the residual monomers reveal rich spectral features that differ from the bulk state. After several rinsing steps with THF, the residual 4,4'- and 2,4'-MDI molecules adsorb in stable states.