I’m trying to interpret the FT-IR result to confirm carboxyl acid or carboxylate in the polymer. As you see the frequency(1500cm-1 ~ 2000cm-1) in the figure, there are two peak, 1640cm-1. 1730cm-1. According to papers, The 1730cm-1 is evidently from the carboxylic acid group. but there are two interpretations of the frequency 1640cm-1. Most researchers said the frequency is from the amide group, other researchers said the frequency is attributed to carboxylate. Actually, I want to interpret the frequency to carboxylate, because I assume there is no amide group now. So I wonder whether I could interpret the two frequencies to carboxylic acid and carboxylate or not. And can the carboxylic acid and carboxylate group be confirmed both in a sample?
Dear Jeon Han Gyeol Thank you for asking this interesting technical question. The band an 1730 cm–1 is clearly indicative for a C=O stretching frequency (see e.g. the useful link cited below). However, only you can answer the question whether your polymer contains carboxylate or amide functional groups, because only you know which starting materials were employed. Amide bands can only be observed when nitrogen-containing starting materials such as amines or isocyanates are employed in the polymerization reaction. Thus is would be helpful if you could provide a few more details about the synthesis in order to give you a more specific answer.
IR SPECTRUM TABLE BY FREQUENCY RANGE
https://www.sigmaaldrich.com/DE/de/technical-documents/technical-article/analytical-chemistry/photometry-and-reflectometry/ir-spectrum-table
Please stay safe and healthy!
Carboxylic acid, say, RCOOH, or carboxylate RCOO-, both habe C=O and comes in the region you have observed in the IR spectrum. C=O and C-OH are different. C-O bond is longer than C=O. CO shows in the region 1000-13000 cm-1. If OH is there, that will appear in the range 3200-3400, say around 3300 cm-1. Next you have to look for C-C-O symmetric and asymmetric stretch around 820 -880 and 1000-1100 cm-1. Now analyze your sample to conclude about its formation and purity. Also use few more other spectroscopic and analytical methods to substantiate the presence of your compound or functional groups.
Best
Balakrishna
Frank T. Edelmann Thank you for answering again! The blue line indicates polymer such as starch that doesn't have amide band, And the orange indicates a material that reacted with the polymer and citric acid!
Balakrishna Maravanji Thank you for advising me!
Good question. If you know about the detailed composition of polymer in respect of specific polymer linkage between the monomers you will be at able to recognize the peaks. The effect of any kind of association ( like inter or intra molecular H-bonding etc.) is also important in such cases because such interactions cause the peak shift.
Dear Ashfaq Ahmad Khan Nur Cebi
Thank you for your help! It was so helpful to me!
Excellent question and a very helpful answer provided by professor @Frank Edelmann.
Dear Jeon Han Gyeol thank you for your kind response and recommendation. I just came across two very interesting freely available articles which might also be of interest to you.
Please have a look e.g. at the following study in which the cross-linking of starch with citric acid has been investigated. The FT-IR of the products are discussed here in detail:
Effect of starch addition on properties of citric acid-bonded particleboard made from bamboo
https://bioresources.cnr.ncsu.edu/resources/effect-of-starch-addition-on-properties-of-citric-acid-bonded-particleboard-made-from-bamboo/
(see attached pdf file)
The authors of this paper come to the conclusion that according to the FTIR analysis the intensity of the carbonyl groups increased with increasing starch content. This was seen as a clear indication of the crosslinking between starch and citric acid.
Also useful with respect to your question could be the following research paper:
Citric acid as multifunctional agent in blowing films of starch/PBAT
Article Citric acid as multifunctional agent in blowing films of starch/PBAT
This article has been posted by the authors as public full text on RG, so that it can be freely downloaded as pdf file. Please see particularly Figure 2S in the Supplementary Material. It shows an FT-IR spectrum which is rather similar to yours in the carbonyl region.
Please stay safe and healthy!
Frank T. Edelmann They were useful paper to me. I should have found on one's own since it is my work... Thank you Pf.! I wll do my best!
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