Unreacted NCO Groups in a Polyurethane Elastomer

This determination is important in all polyurethane fabrieated produets as a means of monitoring quality and to aseertain whether ehain- and erosslink-forming reaetions are eomplete. It ean be used to measure the eure state with respeet to time, temperature and thiekness of a polyurethane part. 

If Aq is the corrected absorbance at /q (OT cm) and A is the observed absorbance at pellet thickness then 

The calculated microequivalents of NCO are then plotted as a function of absorbance and are found to follow Beer s law. 

This technique can also be applied to foams and other samples after they have been commuted into chips, frozen in liquid nitrogen and ground with an agate mortar and pestle. 

Approximately 3-13 mg of foam per K Br disc should be used, depending upon the % NCO expected. 

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