A novel probe design for in situ fiber-optic Raman spectroscopy has been tested and employed for real-time monitoring of an epoxy curing. The epoxy system consists of diglycidylether of bisphenol-A and polyoxypropylenetriamine. The probe consists of a single fiber optic and a small section of Teflon® tubing. The tube acts as a waveguide and sample holder. Raman signal enhancements of 15 × were observed with the employment of the tube compared to those of spectra acquired with the single fiber alone. This analysis studied the C-H stretching region of the epoxide, where previously studies have centered around the fingerprint region. The small volume of the probe and large surface area allow it to be used effectively as a method of polymer thin-film measurement. It is also effective in bulk polymer measurements because of a negligible amount of heat trapped in the sample during curing. This gives the probe a temperature and reaction rate characteristic of the polymer surrounding it. Multivariate analysis was employed to interpret and analyze the numerous spectra taken during analyses. Multivariate techniques show that both curing and sample internal temperature information can be derived from the Raman spectra.
Jeffrey F. Aust, Karl S. Booksh, and Michael L. Myrick, "Novel In Situ Probe for Monitoring Polymer Curing," Appl. Spectrosc. 50, 382-387 (1996)