<title>FTIR of polymers: a 15-year perspective</title>

Abstract

Originally, JR spectra of polymers were measured using a dispersive instrument equipped with an optical element of prisms or gratings to geometrically disperse the infrared radiation'. Using a scanning mechanism, the dispersed radiation is passed over a slit system which isolates the frequency range falling on the detector. In this manner, the spectrum, that is, the energy transmitted through a sample as a function of frequency is obtained. This dispersive JR method is highly limited in sensitivity because most of the available energy is being thrown away , i. e , it does not fall on the open slits and hence does not reach the detector. To improve the sensitivity of JR, a multiplex optical device was sought which allows the continuous detection of all of the transmitted energy simultaneously. The Michelson interferometer is such an optical device and the JR instrumentation which resulted is termed an Fourier Transform infrared (FT-JR) spectrometer2 The Fourier transform process was well known to Michelson and his peers, but the computational difficulty of making the transformation prevented the application of this powerful technique to spectroscopy. An important advance was made with the discovery of the fast Fourier transform (FFT) algorithm by Cooley and Tukey3 which breathed new life into the field of spectroscopy using interferometers by allowing the calculation of the Fourier transform to be carried out rapidly. As computers have improved, the time required for a Fourier transform has been reduced to such an extent that the spectra can be calculated during the time needed for the moving mirror to return to its starting position. When we acquired our first FT-JR instrument, we were impressed with the performance and depressed by the lack of software to manipulate the spectra. Since the infrared spectral data from FT-JR are recorded in digital form, a variety of digital data processing techniques are available to eliminate spectral distortions. These distortions can arise from such things as sample scattering and reflection or from sampling devices such as ATR, photoacoustic, and diffuse reflection. The digital data processing techniques are also used to isolate spectral features for study and quantification.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.