Activity of Diisocyanate

Diisocyanates can vary in reactivity, although no indication of this is given by normal analytical procedures. A simple measure of this reactivity can be obtained empirically by reaction of the diisocyanate with a suitable polyol used as a control. 

To 100 g of dried polyethylene adipate (mol. wt 2000) at 130°C is added 30 g of the diisocyanate and the mixture is continuously stirred. The temperature of the mixture is measured. Upon addition of the diisocyanate the temperature initially falls but as reaction proceeds the temperature rises to a maximum before once again beginning to fall. The time between adding the diisocyanate and reaching the maximum temperature can then 

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