Comparative studies of chemical kinetics of an epoxy‐amine system

Chemical reaction kinetics of an aliphatic diepoxy‐diamine system (DGEBD/4D) has been studied between 50°C and 95°C by two different calorimetric techniques; DSC in isothermal conditions on the one hand, conservation in thermostated tubes with successive extractions of samples studied by DSC in the dynamic temperature mode on the other hand. Experiments show that the kinetics determined by isothermal DSC are systematically faster than those obtained with the other technique, this advance starting during the initial phase of the reaction. We show that this gap comes from the mass difference between the samples used in the two techniques, and can be explained by two different reasons. On the one hand, there appears a delay in the attainment of the thermal equilibrium at the beginning of the kinetics in the thermostated tubes, the samples having a greater mass. On the other hand, experiments have shown that there is a catalytic effect caused by the contact of reactive system with air (probably due to the action of atmospheric water). The area/volume ratio of samples being greater for samples studied by isothermal DSC, the catalytic effect is favoured to a greater extent in the case of this technique, which induces a faster rate of reaction at the beginning of the kinetics. So, as the kinetic curves x = f(t) have different forms, they are described by different kinetic models. The Spacek‐model adequately describes the kinetic curves determined by isothermal DSC, with exponent values p = 1.20 and q = 0.45. The curves obtained by the technique of conservation in thermostated tubes are well described by the second order autocatalytic model, the ratio of the reactivities of primary and secondary amines having the value n = 1.1. Furthermore the Tg variation curve with the extent of reaction in the thermostated tubes agrees very well with the equation proposed by Pascault and Williams.