Step-scan FTIR and photoacoustic detection to assess depth profile of photooxidized polymer

The extent of degradation of photooxidized materials must be determined pre cisely in order to evaluate its lifetime. Generally, an heterogeneous degre e of oxidation is recorded through the sample thickness. Because, oxidation can be much more important near the surface, a photoacoustic (PA) detectio n of the IR spectrum of the material appears particularly well adapted. A P A detector attached to a step-scan (SS) FTIR spectrometer was used to recor d the IR spectrum of a photooxidized styrene-isoprene copolymer. In order t o evaluate the ability of this technique to perform a depth profile of an o xidized material, the sample was also analyzed using transmission micro-FTI R analysis of cross-sectioned layers. These two techniques allow a complete analysis of the material from its surface to its core. Our main finding is that a PA detection is more suitable to determine the superficial extent o f degradation, whereas the micro-FTIR appears more adapted to analyze the h ulk properties of the material. (C) 2001 Elsevier Science B.V. All rights r eserved.