A Study of Epoxy‐Amine Cure Kinetics by Combining Isoconversional Analysis with Temperature Modulated DSC and Dynamic Rheometry

Abstract

AbstractThe kinetics of curing of diglycidyl ether of bisphenol A (DGEBA) with m‐phenylenediamine (m‐PDA) has been studied by using DSC under isothermal and nonisothermal conditions. An advanced isoconversional method has been applied to the data in order to evaluate a dependence of the effective activation energy on the extent of conversion. The method has been applied to the stoichiometric system as well as to the system with an excess of the amine. The nonstoichiometric system demonstrates an effective activation energy that is practically independent of the extent of conversion. The resulting value (≈55 kJ · mol−1) provides an estimate for the curing reaction of the primary amine. The stoichiometric system demonstrates a decreasing activation energy for both isothermal and nonisothermal cures. The value varies from ≈55 kJ · mol−1 to as low as ≈20 kJ · mol−1. The decrease is explained by shifting the rate determining step from a kinetic to a diffusion regime. The diffusion control is associated with the processes of gelation and vitrification that occur on curing and cause a dramatic decrease in molecular mobility. Dynamic rheometry and temperature modulated DSC have been employed to study these processes.Eα‐dependencies obtained for curing the stoichiometric (open symbols) and nonstoichiometric (solid symbols) epoxy systems (circles: nonisothermal conditions; triangles: isothermal cures).magnified imageEα‐dependencies obtained for curing the stoichiometric (open symbols) and nonstoichiometric (solid symbols) epoxy systems (circles: nonisothermal conditions; triangles: isothermal cures).