A quantitative comparison of Raman and Fourier transform near-infrared (FT-NIR) spectroscopic techniques for the analysis of epoxy curing is performed. It is shown that the Raman technique yields a linear calibration curve much like FT-NIR. Band assignments in the Raman spectrum of diglycidyl ether of bisphenol-A (DGEBA) were performed by studying Raman spectra of smaller model compounds.

Fiber‐optic Raman spectroscopy was used to monitor the curing of epoxy resins in situ for eventual application to polymer composite processing. A 200‐μm diameter quartz fiberoptic sensor immersed in liquid resin was used to obtain Raman spectra for a concentration series of diglicidyl ether of bisphenol‐A in its own reaction product with diethylamine using an 820 nm continuous‐wave diode laser excitation. A Raman peak at 1240 cm−1 was assigned to a vibrational mode of the oxirane (epoxide) ring and its normalized intensity was found to be linearly related to the concentration of epoxide groups in the resin mixtures. Raman peaks at 1112 and 1186 cm−1 associated with phenyl and gem‐dimethyl resin backbone vibrations, respectively, did not change in intensity due to the curing reaction and were used as internal references to correct the Raman spectra for intensity changes due to density fluctuations and instrumental variations during the experiments. Fiber‐optic Raman spectroscopy was used to monitor the extent of reaction in situ for the room‐temperature cure of phenyl glicidyl ether with diethylamine. The extent of reaction of the epoxide groups calculated from the Raman spectra were in excellent agreement with kinetic data from Fourier transform near‐infrared absorbance measurements made under the same conditions. © 1994 John Wiley & Sons, Inc.

In situ measurements were made of several organic chemical reactions in supercritical water using fiber-optic probes, near-infrared excitation and CCD array detection. The reactions studied include the conversion of cyclohexene to cyclohexane and benzene in the presence of a platinum catalyst, conversion of cyclohexanol to cyclohexene in the presence of a cobalt catalyst and the homopolymerization of styrene. Transition to the supercritical state was marked by a sudden decrease in the background and the appearance of intense Raman bands for dissolved organic compounds. The results indicate that this method of study is both sensitive and rapid enough to permit kinetic measurements, even when reactions are completed in less than 2 min.

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