In situcure monitoring of epoxy resins using fiber‐optic Raman spectroscopy

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Abstract
Fiber‐optic Raman spectroscopy was used to monitor the curing of epoxy resinsin situfor 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−1was 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−1associated with phenyl andgem‐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 reactionin situfor 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. This article is a US Government work and, as such, is in the public domain in the United States of America.