Adding to Dr. Banhegyi's comments, you can also use equivalent wt. provided by the manufacturer of the reactants. Much like mol/g, eq. wt. is the weight in g that delivers 1 mole of -OH or -NCO. An index of 1 is appropriate for solvent systems. However, for waterborne formulations, an index greater than 1 is recommended due to the competing reaction of isocyante with water. In general, higher indexing will promote higher crosslinking, higher tensile strength, and better chemical resistance.

If you look at an isocyanate datasheet, you will find the wt% NCO content of the given product. Using the molecula weight of the NCO group you can calculate the mol/g concentration of the NCO group. In the case of polyols you have the so-called OH number, from which you can get the OH wt% and using the molecular weight of the OH group your can calculate the mol/g concentration. The isocyanate and the polyol components should be applied in such a weight ratio that the molear ratio of NCO and OH is close to one.

See teh calculation at: http://www.helpdesk-paints-coatings.com/2010/08/calculation-required-isocyanate-in.html

Adding to Dr. Banhegyi's comments, you can also use equivalent wt. provided by the manufacturer of the reactants. Much like mol/g, eq. wt. is the weight in g that delivers 1 mole of -OH or -NCO. An index of 1 is appropriate for solvent systems. However, for waterborne formulations, an index greater than 1 is recommended due to the competing reaction of isocyante with water. In general, higher indexing will promote higher crosslinking, higher tensile strength, and better chemical resistance.

Dear Friend go through the text book

"Chemistry and Technology of Polyols for Polyurethanes"

http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCAQFjAA&url=http%3A%2F%2Fwww.amazon.com%2FChemistry-Technology-Polyols-Polyurethane-Ionescu%2Fdp%2F1859575013&ei=w1TOU5PfIMfK0QWM8YD4Cw&usg=AFQjCNFNL-rE3X84HfGxxVubAqmR35NJLg&sig2=QMiCF2I_aeXx9tjjstBJ5Q&bvm=bv.71198958,d.bGE

you will find solution

What is the normal NCO content in moisture curable PUR adhesive.  I have one adhesive with 2.8% NCO and one with 7.9% NCO.  Which one would be better in terms of long term thermal stability?

Moisture curable PUR adhesive is considered to be a pre-polymer.  The final cross linking takes place in presence of moisture.

f=(Hydroxyl Number*Mw)/56100

where f is functionality,

Mw is the molecular weight of the polyol