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I’m having trouble identifying the peak around 3,75 ppm in the 1H-NMR spectrum of polystyrene measured at 400 Hz in CDCl3. Could someone please provide their perspective on it? I see it appear in a lot of polystyrene spectra but never know what it could be caused by. Thanks in advance!

NMR of polystyrene (1)

NMR of polystyrene (2) this time without bromine as an end group

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  • $\begingroup$ Maybe it's from terminal groups. $\endgroup$
    – Mithoron
    Commented Dec 24, 2023 at 12:41
  • $\begingroup$ I thought so too, just a bit confused which ones, and why would those peaks be so shifted. $\endgroup$
    – yumocci
    Commented Dec 29, 2023 at 16:39

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There can be multiple causes of this kind of trace impurity in a 1H-NMR spectrum. For example trace solvents.

What I think is the most likely cause (it depends on the synthesis used), is that this peak is caused by a trace initiator or trace terminating agent. For example a brominated alkene chain.

I wouldn't worry about it too much as the integral is very small.

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  • $\begingroup$ Got it! Thank you so much for your answer. $\endgroup$
    – yumocci
    Commented Dec 25, 2023 at 8:13

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