A polymer chain containing 45 monomer units out of which only one monomer has -COONa group rest 44 monomer units are having -SO3Na group. Is it possible to detect the C=O group via FTIR? Any suggestion to detect the presence of this C=O group? Thank you in advance.
Hi Ranjit De,
Depending on the FTIR equipment you intend to conduct the analysis, yes, it would be possible to detect the C=O group of your polymer. No problem.
However, if you could conduct 13C NMR experiments, you would observe the ~190-160 ppm signal related to C=O group. I guess the 13C NMR strategy would be more efficient.
Regards
To detect -COONa when it's content is just above 2-molar% by using FTIR is a challenging task, yet, I think it is possible.
In your favor work the following factors:
1. The extinction coefficient of COO- is rather high (above 100)
2.The position of COO- band is around 1600-1550 cm-1 (as. C=O stretching)
is far away from -SO3Na (1250-1100 cm-1)
But the main problem you'll face is that -SO3Na grouppings - possess the surfactant properties. This means that all the --SO3Na units will be on the surface of your material, while the -COONa - in the bulk (inside). So, in order to detect the -COONa - you will have to cut your sample (for to get inside) - and to measure the spectrum by ATR-FTIR technique. According to my experience - this is the only way to solve your problem by using FTIR.
Good Luck to you ! And please write me - if the approach which I described turned to be successful.
Leonid
Dr. Leonid V Vladimirov,
Thank you very much for the valuable suggestion. I shall proceed for ATR-FTIR. Should it be okay to use the powder form of the polymer sample? May I know the reason behind your suggestion to go for the ATR-FTIR technique? Also, how do I cut my sample to get inside to measure the ATR-FTIR spectrum. Thank you again.
Ranjit
A sample of your polymer will contain a good number of macromolecules which means that the single carbonyl of -COONa will recur many times to an amount that can be detected by FTIR. A band, of reasonable length, will appear in the region 1600-1700 cm-1 or close to this range in the IR spectrum.
When I was a postgraduate student, I found out that C-13 NMR was the most reliable technique of characterization. So if it is within reach, then apply it to get good results.Wishing you success.
Dr. Leonid V. Vladimirov, thank you for your suggestion. It seems that the FTIR using ATR technique works well. Both the KBr pallet and ATR techniques are tried, ATR technique turned out to show very low noise and clear distinction between peaks. Thanks for this. Now, I need to decide whether the peaks appearing around 1701 and 1599 cm^(-1) are to be considered from -COOH group or -COONa group as I have converted the -COONa group to -COOH group by treating it with HCl (at pH 1). I expect the >C=O group is from -COOH. But how to confirm? Thanks in advance.
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