Polymer Composition by FT-IR

Hi All,
Can someone help me with that? Sorry for the long explanation of my case…

I am trying to employ FT-IR (ATR) for comparing the real composition against the theoretical composition of a copolymer series. I have synthesized the homopolymers of monomers X and Z and then the copolymers at different theoretical composition (5, 10, 25 and 50 mol% of monomer Z) of both monomers.
Then I got the spectra of all samples employing the ATR technique and identified the following peaks:
- (1461cm-1) present in all samples/spectra's, which I have used as an internal reference.
- (985cm-1) present in spectra of homopolymer X and the copolymers. I have assigned it as a characteristic peak from the monomer X.
- (1104cm-1) present in spectra of homopolymer Z and the copolymers. I have assigned it as a characteristic peak from the monomer Z.

Finally I plotted the absorbance ratio of “monomer Z” (1104/1461) and “monomer X” (985/1461) against the theoretical composition. The final plots are non-linear ones – the “monomer Z” one shows a negative deviation from the linear behavior and the “monomer X” one shows a positive deviation.

Is this a correct approach and can I suggest that the copolymers are "monomer X" richer?

Thanks!

I am sorry to tell you that FTIR is very bad for quantitative analysis. Besides ATR is useless because there is not light path using it.

I have not used an FTIR for this purpose but from what I recall it should be possible. What I would like to say is that if you have substantially different reactivity in your monomers then yes it is possible to have that occur. The magnitude of this effect relies greatly on the geometry and kinetics of the process.