ADSORPTION OF 4,4'-METHYLENE DIPHENYL DIISOCYANATE (MDI) ON NATIVE COPPER

摘要

This in situ FTIR-ERA spectroscopy study shows that adsorbed 4,4'-MDI molecules undergo notable qualitative (e.g. new bands) and quantitative (after some rinsing steps) changes of their vibrational state on native surfaces of Cu. Once the 4,4'-MDI is brought into contact with the metal surface (1st rinse), remarkable differences between the bulk-like spectrum arise. As ERAS provides the spectrum of the complete deposited layer, the various adsorption states after the MDI rinse are not distinguished - except the new sharp peak formed at 2300 cm~(-1) (cf. Figure 3). Other new IR bands appear and reveal that urea species formed by reaction of weakly adsorbed isocyanate with physically adsorbed water on the substrate. These urea species and the major part of isocyanate are washed away with the 2nd rinse. Therefore, these molecules establish only weak adsorption. After several rinsing steps with THF the remaining 4,4'-MDI molecules absorb in rather stable states. The characteristic MDI bands and the appearing new spectral features suggest that the strongly adsorbed isocyanate groups and the pendant phenyl rings stick in some preferential orientation due to strong interactions with the native oxide layers on Cu. That could be related to chemical adhesion but final proof is needed by appropriate quantum mechanical modelling.