Fluorescence Characteristics of Cure Products in Bis(maleimide)/Diallylbisphenol A Resin

Curing bis(maleimide) (BMI) with diallylbisphenol A (DABPA) results in the formation of a high-performance thermoset resin. A variety of reactions in which maleimide units are converted to succinimide moieties have been proposed. In order to make spectral assignments for the fluorescence behavior observed during the cure of BMI/DABPA resin and to assess the likelihood that certain types of reactions take place during resin cure, several succinimide model compounds were synthesized from N-phenylmaleimide (NPM) and characterized. These model compounds gave fluorescence signals which were red-shifted by 40 nm or more from the emission maximum in DABPA resin, while no fluorescence was observed from the BMI. The BMI was found to quench the fluorescence from DABPA and a Stern−Volmer quenching constant was determined for this pair. Relative fluorescence quantum yields were determined for the model compounds. The DABPA resin component was found to have the highest quantum yield and is likely to be responsible for most of the fluorescence near 356 nm when the resin is excited near 280 nm. A succinimide derivative which arises from a Diels−Alder−Ene reaction sequence was found to have a higher quantum yield than other succinimides which were investigated. This type of structure might be responsible for most of the fluorescence observed in the long wavelength regions. Fluorescence peak shapes and peak positions were found to have a concentration dependence.