Hi all,

I am currently investigating the deblocking behavior of hexamethylenedicarbamoylcaprolactam (HDCL) to hexamethylene-1,6-diisocyanate (HDI) by temperature.

The graph shows the absorption as a function of temperature of HDCL (>70%) dissolved in caprolactam.

Due to deblocking, I would have expected a strong band at ~2280 cm-1 for the -N=C=O as stretching vibration, but it is missing.

Does anyone have an idea why such a strong absorption occurs especially at 1680/1650 cm-1?

My current explanation is that due to the high concentration of deblocked HDI and small amounts of moisture during the measurement (no inert gas atmosphere), urea is formed.

What are your thoughts on this?

Many thanks in advance!

Michael