Determination of exact absorption behaviour in the mid-infrared spectral range of poly(methylmethacrylate) by Fourier transform infrared reflection spectroscopy
✍ Scribed by Brogly, Maurice; Bistac, Sophie; Schultz, Jacques
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 318 KB
- Volume
- 44
- Category
- Article
- ISSN
- 0959-8103
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✦ Synopsis
In the present work we demonstrate that infrared absorption frequencies and band shapes of poly(methylmethacrylate) (PMMA) homopolymers vary strongly with the type of spectra recorded. The reason is that, in general, any measured optical quantity, such as absorption, transmittance or reÑectance, is a complicated function of the refractive index, n(l), and the absorption index, k(l), of the material. KramersÈKronig analysis is applied to external reÑection spectra from a single polymer surface measured near the normal incidence angle. Absorption spectra, k(l), are then deduced and used to calculate grazing angle specular reÑectance, attenuated total reÑectance, di †use reÑectance and transmission spectra. Then, it is shown that the calculated spectrum for each experiment accurately predicts the experimental one, proving that di †erences are optical artifacts and not true sample di †erences. Exact peak absorption for PMMA is 1730 cm~1 and should be taken as a reference value for the calculation of frequency shifts for further physico-chemical interpretation such as speciÐc interactions or molecular orientation.