Dear Kiruthika Mohan

The infrared spectrum of a polymer or rubber is a profile of its absorption characteristics plotted against infrared wavenumber (or frequency). It is generated when infrared radiation interacts with the molecular moieties that constitute the polymer or rubber material. It is a distinctive property (a “fingerprint”) of the polymer or rubber sample in the form, manner and environment in which it is being examined. It is based on the absorption of infrared radiation at frequencies that match those of the normal modes of vibration within the macromolecule. These absorption features are characteristic of the molecular configuration, sequencing and conformation, and state of order. Absorptions by internal vibrations predominate in the mid-infrared region (ca. 4000–400 cm−1); they involve a few selected atoms in a molecular (functional) grouping, which is a sub-set of those constituting the macromolecule. External vibrations, such as lattice vibrations, which involve segments of macromolecules in crystalline regions, tend to occur at low wavenumbers (

If you want to identify the presence of your polymer, you need to know the ref IR of your polymer's environment. Its characteristic peaks can be overlaped with that of environment, so that different characteristic bands should be used subject to the environment.

I assume you are working with unknown samples. In order to identify the presence of a particular polymer you should start by focusing on what type of polymer you have (Is it a hydrocarbon polymer, a polyester, a polyamide, etc. ?) and then go into a more detailed interrogation (Is it crystalline or amorphous? Which is the major constituent? Is it a copolymer? etc. ). The appearance of the vibrational spectrum of a polymer is the result of a complex superposition of many effects. A polymer sample involves a large collection of molecules of differing chain length, which will determine the appearance of the fine detail of its spectrum. The vibrational spectra may also be affected by their thermal/processing/environmental history, the method of sample preparation/examination, and so on. Full or close identification is usually achieved by empirical or computerized pattern-matching a spectrum with that of a standard reference spectrum. In short, you should go with a systematic approach and use the rules that normally apply to pick out characteristic bands and then work out, at least generically, what the material is.

Here are some helpful references:

• N.J. Everall, P.R. Griffiths, J.M. Chalmers, Vibrational Spectroscopy of Polymers: Principles and Practice, Wiley, 2007.
• A.H. Kuptsov, G.N. Zhizhin, Handbook of Fourier Transform Raman and Infrared Spectra of Polymers (1st Ed.), Elsevier, 1998.
• J.L. Koenig, Spectroscopy of Polymers (2nd Ed.), Elsevier, 1999.

Dear Ali, please check:

B. Smith, Infrared Spectrum Interpretation, a Systematic Approach (CRC Press, U.S.A., 1999).

It's a lovely book, not only to start with FTIR for polymers and organics, but it will accompany you always. It presents a useful guide to identify different groups based on characteristic bands for organics.

Thank you everyone for your response...

I am working with pre-processed environmental samples (soil and water) for polymer identification.

As Ioana Maria Cortea mentioned, I have used pattern-matching software called openspecy for matching the spectrum. Even if the pearson coeffeicient is taken as 0.5 and above to filter the number of matches, it is still difficult to narrow down the matches.

Is it possible for one spectrum of unknown sample to show match with spectrums of different types of polymer?

Kiruthika Mohan, please see the below discussion on RG, perhaps it is of help:

https://www.researchgate.net/post/What_percentage_of_library_matches_are_generally_acceptable_in_microplastics_analysis