FLUORESCENCE STUDIES OF DIAMINODIPHENYL SULFONE CURING AGENT FOR EPOXY CURE CHARACTERIZATION

Fluorescence emission and excitation of a commonly used aromatic diamine curing agent, 4,4'-diaminodiphenyl sulfone (DDS), were studied during the curing process with a bifunctional epoxide or a tetrafunctional epoxide. As the curing proceeds, both the emission and the excitation spectra exhibit red shifts of about 25 nm for DDS due to the conversion of the primary amine groups in DDS to tertiary amine groups. Matrix effects such as the polarity decrease and the viscosity increase on the fluorescence spectra of the tertiary amino DDS (tt-DDS) were found to be small. The excitation spectra provide sharper peaks than the emission spectra, even though the overall spectral red shift in both spectra for DDS is about 25 nm. Based on the spectra of the model DDS cure species and the curing kinetics, the excitation spectra were simulated as a function of the extent of amine reaction. The result shows that the excitation spectral shift can be easily correlated to the extent of amine reaction. The extent of epoxide reaction based on IR analysis was found to be correlated almost linearly with the DDS excitation spectral shift. These results on the excitation spectra provide a basis for cure monitoring of the epoxide-diamine networks from the intrinsic fluorescence of the diamine curing agent DDS.