Comparative study on the curing kinetics and thermal properties of a new series of diglycidyl esters of bis(trimellitimide)s

Abstract

AbstractThe non‐isothermal curing behavior of a new series of epoxy‐imide resins based on trimellitimide structures, synthesized in a three‐step procedure, were evaluated by differential scanning calorimetry. The chemical structures of the synthesized intermediates and their corresponding epoxy‐imide resins were characterized and confirmed by Fourier‐transform infrared spectroscopy and 1H‐NMR spectroscopy. The imide‐containing resins, also a medium molecular weight bisphenol‐A based epoxy (as reference) were cured by dicyandiamide. The variation of apparent activation energies (Eα) with conversion was then calculated by various differential, as well as integral isoconversional methods. Furthermore, the thermal stability of understudied systems was evaluated by thermogravimetric analysis (TGA). The results showed that the determined melting temperatures of epoxy‐imide resins were significantly higher than that of the reference one, but were still within the range of powder coating application temperatures. In contrast with the reference, the imide‐containing systems showed the dependency of Eα as a function of the curing conversion and the values of Eα at the onset of their curing reactions were considerably higher than that of another, ca. 111.6–155.4 kJ/mol against 50.7 kJ/mol, which approached the reference value at the end of the curing reactions. The evaluation of reaction mechanisms with the progress of the curing reactions by the methods of Friedman and Malek revealed the traits of autocatalytic behavior, despite the predominance of the nth‐order reaction mechanism. The TGA data also showed that the cured epoxy‐imide samples had lower degradation rates, extended stability windows, and enhanced flame retardancy compared with the reference resin.