Diffusion and Diffusion-Controlled Kinetics during Epoxy-Amine Cure

The molecular diffusion and the diffusion-controlled kinetics during curing of an epoxy-amine resin have been studied. The diffusivity was estimated using an approach based on the dielectric analysis of the resin system. At low conversions, the decline of the diffusion coefficient is relatively slow while, at higher conversions, the diffusivity drops significantly even with a small advancement of cure. The normalized diffusion coefficient was in agreement with the predictions of the free-volume model of Huguenin and Klein but disagrees with those of the cooperative rearrangement model of Havlíček and Dušek. This discrepancy was attributed to an assumption of the cooperative rearrangement model. Based on the Rabinowitch model and the diffusion coefficient obtained, a diffusion-controlled kinetic model has been developed which accounts for the diffusional limitations on the cure kinetics and adequately predicts the experimental conversion profiles even at high conversions.