Cure characterization of unsaturated polyester resin by fluorescence spectroscopy

A strong fluorescence emission was observed during cure of an unsaturated polyester resin containing about 30% styrene by weight. As the cure proceeded, the emission intensity at 306 nm increased. Model compound studies confirmed that the unsaturated polyester component exhibited negligible fluorescence when excited at 250 nm where styrene has strong absorption. Based on the studies of styrene/polystyrene mixtures, the fluorescence emission at 306 nm was attributed to a reduced inner‐filter effect of styrene monomer. Fluorescence intensity changes following cure at 75°C were correlated to the extent of styrene conversion determined by FT‐IR spectroscopy, demonstrating that the fluorescence measurement is more sensitive to styrene conversion in the later stages of cure than conventional IR measurements. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2446–2450, 2004