Surface/Interfacial Changes During Polyurethane Crosslinking: A Spectroscopic Study. V

摘要

Crosslinking reaclforis and stratification processes in polyurethane films were investigated using attenuated total reflectance (ATR) FTIR spectroscopy. The HDI trimer levels near the film-substrate (F-S) interface appear to increase at the early stages of reactions, and after reaching a maximum, decrease. This is attributed to solvent depletion and subsequent film shrinkage, thus causing local NCO concentration changes. At the later stages of crosslinking reactions, stratification of the 1,6-hexa-methylene diisocyanate (HDl) trimer occurs, with higher concentration levels at shallower penetration depths from the F-S interface. At the same time, NCO-containing , groups assume preferentially parallel orientation to the F-S interface. On the other t, hand, H-bonded carbonyl groups tend to orient themselves in a perpendicular direction.Quantitative analysis indicates that at extended reaction times the amount of H-bonded C=O groups at shallower penetration depths increases and their orientation tends to be more random, which is correlated with migration toward the F-S interface.