Diisocyanate deficient

Data for Polymers 7 19 Prepared from Balanced and Diisocyanate-Deficient Recipes... 

It can be seen from Table XIII data that control Polymer 7 is a high molecular weight and high quality polyurethane whereas the modified polymerization yielded lower molecular weight Polymer 19 with good but lesser properties. The lowest final (16 minute) [NCO] was obtained in the polyurethane prepared with a diisocyanate deficiency in the charging recipe. 

This formulation contains 2-55 mol of difunctional hydroxy compound compared with 2-86 mol of diisocyanate, an excess of 0-31 mol of diisocyanate. The presence of 0 5% water in the Desmophen 2000 would remove the excess diisocyanate and result in the equivalent of a deficiency of 0-24 mol of diisocyanate. Since an excess of diisocyanate is required the water content of the Desmophen 2000 must be reduced, and to obtain consistent results it is recommended that it be reduced to less than 0 05%. Apart from altering the stoichiometry, the water can cause premature chain extension and gas evolution, both of which are detrimental to the process. It is obvious that polyesters must be very dry before being synthesized into the prepolymer. 

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