June 07, 2020, 03:21:57 AM
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Topic: Monomers/Polymer Quantitative Measurement with 1H NMR Spectrum?  (Read 176 times)

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Offline Alex1991

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Hello guys,

my name is Alex and i am currently doing my studies in chemistry.
I am contacting you now as i am currently doing quantitative research on my polymer synthesis, more precisely monitoring the conversion from my monomers to polymer and also determining how much of my monomers i have still present.

In the attachment you will find the spectra of the polymer where you can besides the structure and reaction, also see the percentages of the monomers still present together with % of the polymer which represents the conversion. The measurements were done by a lab technician from a separated NMR department.

The problem is now, that the lab technician doesn't know exactly how do the equations for the calculation of % of polymer or remaining monomers looks like as he is using a special program to do that, where he just selects the peaks belonging to different structures.

As I would like to understand how this is done, could you please help me and explain to me how this is done and if it is not too much to ask, write the equations which you think are used for this calculations?

Thank you very much for your answer!
Best regards,
Alex

Offline wildfyr

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Re: Monomers/Polymer Quantitative Measurement with 1H NMR Spectrum?
« Reply #1 on: March 29, 2020, 10:37:54 PM »
You need the precise peak ppm locations in order to even have a chance at this. Also need the same for the monomer NMRs. You have to see which of these extra peaks are just junk and which are monomer, than take the ratio to the polymer peak.

The easiest and frankly more accurate answer here, BTW is to use gravimetry and GC to sort this out. You just add, say, 10mg of crude sample to a gc solvent, shoot it in, and use a standard to see what the concentration of volatile monomer is.

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