The use of front-surface specular reflection FT-IR spectroscopy to characterize surface orientation in thick samples of poly(ethylene terephthalate) (PET) has been investigated. It has been shown that, even for samples whose surface uniformity is less than perfect, absorption index spectra of excellent quality are obtained from the Kramers-Kronig transformation. These spectra provide detailed information, both qualitative and quantitative, on the molecular conformation and orientation of the polymer. Of particular interest are the strongly absorbing bands such as the carbonyl and ester peaks, which are generally saturated in transmission spectra. The reflection technique opens up the possibility of obtaining new information on conformational changes and orientation in PET through a detailed study of these peaks.
K. C. Cole, J. Guèvremont, A. Ajji, and M. M. Dumoulin, "Characterization of Surface Orientation in Poly(ethylene terephthalate) by Front-Surface Reflection Infrared Spectroscopy," Appl. Spectrosc. 48, 1513-1521 (1994)