Comparative DSC kinetics of the reaction of DGEBA with aromatic diamines. II. Isothermal kinetic study of the reaction of DGEBA with m-phenylene diamine

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In the first part of the present series the non-isothermal kinetics of the reaction of an epoxy resin based on diglycidyl ether of bis-phenol A (DGEBA) with m-phenylene diamine (mPDA) was studied. A four step kinetic analysis was applied using differential scanning calorimetry (DSC) data. It allowed us to confirm the validity of the three molecular autocatalytic model of this reaction, as well as to obtain reliable kinetic data in programmed temperature mode.The isothermal study of the DGEBA–mPDA reaction was performed applying a similar kinetic approach: (i) analysis at the peak maximum of the DSC curves; (ii) apparent activation energy analysis of the isothermal DSC data; (iii) integral and differential curve fitting methods; and (iv) modeling of the reaction and comparison of the model with the experiment.It was established that the overall kinetic parameters measured under programmed temperature conditions sufficiently well described the isothermal shift of the DSC curves along the logarithmic time scale, especially the initial stage of the reaction. A more precise analysis of the data showed that the isothermal DSC kinetics obeyed a formal model whose power exponent was approximately 2.5, or it was not well represented by the mechanistic-like three molecular autocatalytic velocity equation. Nevertheless, the activation energy of the autocatalytic rate constant determined at constant temperature mode, i.e. Ea,i=50.67kJmol−1, was found out in close agreement with the one obtained previously in programmed temperature mode, Ea,n=50.50kJmol−1. On the contrary, the ratio of the impurity catalytic to autocatalytic rate constant was slightly temperature dependent.