Chemico-diffusion kinetics of model epoxy-amine resins

The curing reaction of stoichiometric mixtures of the diglycidyl ether of bisphenol-A with difunctional diamino diphenyl methane and monofunctional aniline was studied using isothermal differential scanning calorimetry over a range of temperatures. High temperature data, beyond the diffusion controlled range, was used to fit the kinetics to an autocatalytic rate equation to determine the chemically-controlled rate constants. In order to model the effect of diffusion on reaction rate, the Couchman-Karasz equation was used to fit the glass transition temperature (T-g) of partially cured samples to the degree of conversion. This T-g/conversion relationship was used in the Williams-Landel-Ferry (WLF) equation to calculate the diffusional rate constant during cure. The chemical and diffusional rate constants were combined in the Rabinowitch equation to model the overall rate constant for the reaction. This model predicts rate/ conversion data and has reasonable agreement with the experimental curves. Differences between theory and experiment were discussed in terms of the dependence of the diffusion coefficient on molecular size and the non-universality of the WLF constants. (C) 1997 Elsevier Science Ltd.