How to calculate the molar ratio for the components of a polyurethane in a stoichiometric value? For example, if I have: Trifunctional polyolPPG (MW = 1000 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?
polyol: PPG, f=3, Mw=1000, E=1000/3=333
isocyanate: MDI, f=2, Mw=250, E=250/2=125
chain extender: 1,4BDO, f=2, Mw=90, E=90/2=45
If fix iso index (r)=1.03
So r=isocyanate(En)/(polyol, En+chain extender, En)=2.06/(1+1)
En=grams/E, E=Mw/f
so PPG=333g , MDI=257.5g, 1,4 BDO=45g , HS%=27.3%, r=1.03
I USED PPG1000 INSTEAD PTMEG1000 I USED NORMALLY, BUT I HAVE NOT RECEIVED THE SAME CATATERISTICHE RESIN POLYURETHANE .WHY??
Helen,
F is the number of reactive groups per mole of compound. The polyol is a trihydroxy compound and therefore has an f of 3 while the diidsocyanate and chain extender have fs of two as each has two reactive groups per mole of compound. Dividing the molecular weight of the compound by f gives the weight per equivalent of reactive group. The number of equivalents of the polyol and chain extender must equal the number of equivalents of isocyanate groups. The calcualtions given by Alex Lin are correct. he has calcualted in a slight excess of isocyanate groups (3%).
Rezvan,
Changing the polyol from poly(propylene glycol) to poly(tetramethylene glycol) will result in a polyuretahne with different properties/structure. Any change in the nature of the reactants will result in changes to the structure and therefore the properties of the polymer.
Just a suggestion.
If you want to have a stoichiometric controlled Polyurethane, you can not rely on the polyol molar mass found at the package. It is essential to know with accuracy the content of OH groups of the polyol (e.g.: mols of OH/ gram of polyol). Many techniques are available for such characterization, from tritation to spectroscopic analyses. One of the best techniques I have found make use of ¹H NMR and is very fast and accurate, I describe the use of this thecnique in this article:
European Polymer Journal, 62, 2015, Pages 77–86
http://www.sciencedirect.com/science/article/pii/S001430571400384X
Again, for general purposes, this accuracy are not necessary.
Could any one explain, whats means by stannous chloride (SnCl2·2H2O) andthioacetimide (C2H5NS) with molar ratio of sulphur and tin pre-cursors maintained as 6.
How to calculate moalr ratio 1:2 for acholine chloride and MAA
Dear friends,
does anyone know that how you can open the cells of a polyurethane foam in this way, that is to reduce the density? I tried adding more water or adding NaCl .. but it doesn't open that much.
Thanks in advance
Rezvan
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