Isocyanates

Isocyanates are chemicals that react with hydroxyl-bearing chemicals and amino-bearing chemicals to form polyurethane and polyurea linkages, respectively. Isocyanates can be divided into aliphatic isocyanates and aromatic isocyanates.  Aliphatic isocyanates are UV stable and do not easily degrade or discolor when exposed to UV radiation.  Aliphatic isocyanates react slower than aromatic isocyanates, but are typically more expensive and are often more hazardous to handle than their aromatic cousins, 

There  are several key characteristics which define what performance properties a given isocyanate will impart in a given polyurethane system.  These characteristics include:  the NCO equivalent weight, the %NCO, and the functionality of the isocyanate. 

NCO equivalent weight is the number of grams of a given product that contains one equivalent of isocyanate groups (NCO).  One equivalent of NCO groups is 42.02 grams/mol

%NCO = 4202/NCO equivalent weight.

Isocyanate functionality refers to the number of NCO groups per  molecule.  Increasing the number of NCO groups results in greater crosslinking.  Greater crosslinking yields stiffer, harder products with enhanced chemical and thermal resistance.

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