For example, if I have:
Trifunctional polyol (MW = 6000 g/mol)
Diisocyanate (MW = 250 g/mol)
Chain estender (WM = 90 g/mol)
How much do I need in grams of (each one) for the stoichiometric molar ratio?
If you use a two-step synthesis, first you prepare the isocyanate end-capped polyol: you should add 3 mols of the diisocyanate (750 g) to 1 mol triol (6000 g) and have it reacted. Afterwards you have 3 isocyanate end-groups. The extender is usually a diol, therefore you have to react 3 mols of diol with 2 mols of the trivalent end-capped material, i.e. 270 g diol with 13500 g trivalent prepolymer. Of course, you should use proper catalysts.
Hello Gyorgy Banhegyi & José Alberto Salazar-Jiménez ....above discussion helped me also.... furthermore can i have detail of suitable catalyst? or any calculation for this reaction to calculate exothermicity ?
Most frequently used catalysts are dubutyl tin dilaurate, and teritary amines. For a more detailed duscussion see https://en.wikipedia.org/wiki/Polyurethane
Reactionheat should be measured or if you have your formulation you may look for relevant literature data
thanks Gyorgy Banhegyi , mainly i m worried about Temperature during reaction, how much exothermicity creates,
If you have a thermocouple, mix a smaller amount (about one cup), put it onto a plastic cup and let it react. Pur your thermocouple to the mixture and you will have rough estimate of temperature rise.
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