Monitoring of curing process by fluorescence technique. Fluorescence probeand label based on 5-dimethylaminonaphthalene-1-sulfonamide derivatives (DNS)

The curing reaction of glycidyl ether bisphenol A (DGEBA) with n-butyl amin e and/or N-methylethylenediamine was monitored by fluorescence spectroscopy . 5-Dimethylaminonaphthalene-1-sulfonamide (DNS) fluorophore was used as a probe and/or label. Fourier transform infrared (FTIR) analysis revealed tha t the rate constant for the addition reaction of the primary amino group hy drogen of n-butylamine to the epoxide ring is more than four times larger t han that arising from a secondary amine. Significant differences have been observed between the fluorescence behavior of the DNS as a probe and label, especially in the system DGEBA-n-butyl amine. Integrated fluorescence inte nsity for the DNS label, in contrast to the DNS probe, indicates the most i mportant changes in chemical transformations of this reaction mixture (the onset of tertiary amino groups and maximum concentration of secondary amino groups). Similarly, the dependence of the half-bandwidth on the epoxy grou ps conversion for the DNS label shows these stages of the curing reaction a s well. In the system DGEBA-N-methylethylenediamine, the reactivity of the secondary amino group hydrogen is higher than that of the primary amino gro up. A change in slope of the dependence of integrated fluorescence intensit y on epoxy group conversion clearly indicates the gel point and entry of th e system into the glassy state. The DNS probe does not sense any of these c hanges. From the emission spectra of the DNS probe and/or label, the averag e value <v> = SigmaI(F)(v)v/SigmaI(F)(v) of the emission band position has been correlated with the epoxy group conversion determined by FTIR. Smooth dependencies were obtained in all cases. This enables one to monitor on lin e and in real time the epoxy group conversion.