Cure monitoring of epoxy resins by excimer fluorescence

Abstract Experimental studies are reported of the steady-state fluorescence of the excimer probe 1,3-bis-1-pyrene propane (BPP) during cure of Epon 828, a bis-diglycidylether epoxy, using 4,4′-methylene-bis-cyclohexylamine (MBCH) as hardener. We find that the ratio of excimer to monomer emission is of limited use for monitoring the viscosity increase that occurs during the cure reaction. However, the monomer emission of the excimer probe shows a substantial increase in intensity during the cure reaction which correlates quantitatively with the known change in viscoelastic properties of the Epon 828/MBCH system. Comparison with similar fluorescence enhancement of the probe 1,4-dimethylaminophenyl-6-phenyl-1,3,5-hexatriene (DMA-DPH) during cure of the Epon 828/MBCH epoxy suggests that the observed enhancement of the monomer intensity of BPP is also due to a decrease in non-radiative decay of singlets as the matrix viscosity increases.