Characterization of Epoxy Cure by UV-Visible and Fluorescence Spectroscopy: Azochromophoric Labeling Approach

摘要

Cure composition, reactivity ratio, activation energy, and weight-coverage molecular weight in two epoxy networks are investigated by an azochromophore labeling technique. The chromophore, p,p'-diaminoazobenzene (DAA), is used to mimic the reactivity of the curing agent, diaminoidiphenyl sulfone (DDS). Reaction of DAA with epoxide produces red shifts, which have been deconvoluted on the basis of band assignments of model compounds. Thus, we obtain compositional analyses of cure products. Fluorescence due to the DAA label increases sharply due to the increasing fluorescence quantum yield of cure products containing tertiary amine rather than to viscosity changes. Fluorescence intensity has been used to estimate composition, based on kinetic differential equations, and these results have been compared with those obtained by UV-vis spectral deconvolution. Primary and secondary amines react at similar rates. The activation energy was estimated to be 16 kcal/mol on the basis of initial rate constants of the amine-epoxy reaction. Our experimental data were compared with the theoretically predicted weight-average molecular weight and soluble fractions. Finally, we compared UV-vis and IR techniques for the extent of cure in two epoxy systems. IR and thermal analyses suggest that DAA reacts a little faster than DDS. This difference in rates can be corrected by using a calibration curve.