Dear All,
I want to know the MW of polyethylene glycol. Please suggest me how to calculate the molecular weight from proton NMR.
Thanking you.
The method I mentioned earlier works only if you can resolve/identify/integrate the end group -CH2OH; this may require high-field NMR. Some articles suggest using the end --CH2OH (this may also require high field NMR, and dry sample/solvent). There is also a paper that suggests using a shift reagent. Quantitative 13C has also been shown to be useful for analyzing PEG. I am attaching some references and spectra.
P.S. The TFA-d is move the OH resonance away from the OCH2's so its integral is not included; it should also remove any possible contribution of moisture. Some people also use dry DMSO-d6 as solvent which hydrogen-bonds with OH.
A simple way to estimate the average molecular weight of PEG from a 1D 1H NMR spectrum is described in the attached. As long as you can identify the end -CH2OH
resonance, this should work. Good luck! AF
Thank you all for your valuable suggestions.
Must we add TFA-d?
Is it possible without that?
The method I mentioned earlier works only if you can resolve/identify/integrate the end group -CH2OH; this may require high-field NMR. Some articles suggest using the end --CH2OH (this may also require high field NMR, and dry sample/solvent). There is also a paper that suggests using a shift reagent. Quantitative 13C has also been shown to be useful for analyzing PEG. I am attaching some references and spectra.
P.S. The TFA-d is move the OH resonance away from the OCH2's so its integral is not included; it should also remove any possible contribution of moisture. Some people also use dry DMSO-d6 as solvent which hydrogen-bonds with OH.
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