Structural investigation of polyurethanes: Infrared spectroscopic investigations of monomeric and polymeric N,N′-diaryl ureas

Abstract

The carbonyl stretching vibration of crystalline N,N′-diaryl ureas at 1640 cm−1 undergoes a very considerable shift to 1700 cm−1 when these compounds are in solution. This finding is of particular significance in connection with the hard segments of polyurethane elastomers. The absence of a carbonyl band at 1640 cm−1 in polyurethane–polyurea systems does not indicate the absence of urea groups or the reaction of urea groups to biuret groups. Urea groups may instead be present in the dissolved, i.e., noncrystalline, form. On the other hand, the absorption at 1640 cm−1 is suitable for the determination of crystallization kinetics.