Abstract
The optical properties and microstructure degradation of 4,4′-diaminodiphenylmethane (DDM)-cured epoxy after 170 keV vacuum electron irradiation were investigated in the paper. It was found that the colorless DDM-cured epoxy turned to be green after electron irradiation. Ultraviolet–Visible (UV–vis) spectra analysis showed that irradiation resulted in two absorption peaks appearing at wavelengths of 406 and 636 nm, respectively. The main absorption at the peak of 636 nm was attributed to n → π* transition and mainly responsible for the green color appearance. Distinguishable cyclohexadienyl-type radicals were detected using electron paramagnetic resonance spectra (EPR), wherein the central peak in the EPR spectrum was assigned to the green chromophore. It is an interesting result that the annealing kinetics of the radical and optical properties after irradiation with fluence of 5 × 1014cm−1 were coincidently found to follow a sum of an exponential and a linear mode with the storage time at room temperature and to have almost equal characteristic time constant. And after infrared spectroscopy analysis, the annealable green chromophore was proposed to be assigned to the quinone-type radical.
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