Cure properties of epoxies with varying chain length as studied by DSC

The cure of diglycidyl ether of bisphenol A (DGEBA) and a homologous series of poly(ethylene oxide) diglycidyl ether (PEODE) epoxy resins with 4,4'-di aminodiphenyl sulfone (DDS) was studied by scanning and isothermal differen tial scanning calorimetry (DSC). The heat of polymerization was relatively independent of monomer structure and chain length when determined by isothe rmal DSC. Variations in the heats of polymerization determined by the scann ing method were attributed to degradative reactions at higher temperatures during the scan. The activation energies determined by scanning DSC experim ents were relatively constant at 61 +/- 3 kJ/mol, However, using an isother mal cure method, the activation energies were found to vary with monomer st ructure and extent of cure, The isothermal kinetics were analyzed in terms of the autocatalytic model on the basis of competing reaction paths involvi ng catalysis by either initial impurities or hydroxyl groups produced in si tu. The activation energies of both reaction paths were found to vary with monomer structure and degree of conversion. (C) 1999 John Wiley & Sons, Inc .