Dear all,
I want to calculate the hydroxyl value or OH functionality of PEG from 1H NMR.
Is it possible to calculate as end functionality as in the other oligomers..?
What will be the degree of deviation from titration methods..?
Please help me with your valuable suggestions.
Thanking you.
With a high field NMR (500 MHz+ preferred, but 300 sometimes works) you can see the methylene of the CH2OH at the terminus. No idea about titration methods, it should be the same if the NMR spectrum is good.
I'm sure there are easily findable papers where people took NMR of end-functionalized PEG
I have checked one 1H NMR spectrum in CDCl3 (300 MHz) and as Jeremy says the signals of one of the methylenes of the end groups appear upfield and the other downfield shifted which allow the determination of OH number. The Mn for this oligomer is about 950 g/mol. An the hydroxyl value calculated is around 124 mg/g.
Can you please give required formulae/equations for calculating Mn and OH number....
I attach a document wiht the equations used to calculate these values
Hello, Antxon,
Thanks for sharing valuable info. I am wondering, from where does 56, 2, and 1000 comes from. I guess 56 is from KOH mol wt. but not sure about 2 and 1000. Can u pls. explain it? Just curious, is it possible to determine Mn from HV?
By definition the hydroxyl value is the number of g or mg of KOH needed for neutralization of the acid that can esterify1 Kg or 1 g of a substance (expresed in g/kg or mg/g). In this case the Mn of PEG determined by NMR is 975. In 1 kg of PEG you will have 1000/975 mol of PEG. You shoud multiply by 2 because every chain of PEG has 2 hydroxyl end groups. Then you multiply by 56 to calculate the mass (g) of KOH that will be required for the neutralization of the acid that can sterify 1 Kg of PEG.
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