Hi Cosimo,

maybe you will the answer here:

Article Modifications of the rigid polyurethane - Polyisocyanurate foams

Or here:

https://www.researchgate.net/post/How_can_I_measure_the_trimerization_conversion_in_the_polyisocyanurate_forming_reaction

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.823.8205&rep=rep1&type=pdf

https://m.remspec.com/pdfs/Urethane%20development.pdf

Regards

Markus

Dear Mr. Christ,

thanks for replying me. I will check the references.

Regards

Cosimo

You can use any band based on the chemical groups that do not show changes during any chemical reactions or physical reactions. However, majority of the IR bands are the contributions from multiple groups and, thus, tend to change the intensity by either chemical reactions or physical structural changes. Aliphatic CH stretching bands, in the region of 3000-2800 cm-1, are usually very stable as the potential energy distribution of these bands are nearly 99% pure. In the case of PU, you have relatively well isolated 2972 cm-1 band. However, PIR lacks this band. Yet, there are multiple bands between 2950 and 2850 cm-1 that appear to be relatively stable. Ideally, you should curve resolve these heavily overlapped bands (there are at least three bands, maybe 4) to be more accurate, but by measuring the height (absorbance), you can obtain quasi-quantitative comparison. Use the intensity of one of the band (the one near 2850 cm-1 might be good) and divide the absorbance of the band you want to compare to normalize the intensity then compare the normalized intensity of two different conditions, such as different reaction times.