Effect of a curing accelerator on the glass transition temperature of non-stoichiometric epoxy amine networks

Networks were prepared from Bisphenol A diglycidylether and 4,4′-diaminodiphenylmethane both in the presence of different amounts of imidazole and in the absence of any accelerator. The ratio of epoxy groups to amino hydrogen was varied: the networks were made with amino hydrogen excess, a stoichiometric ratio of epoxy groups to amino hydrogen, and an epoxy excess. The resulting networks were investigated by thermomechanical analysis, by torsion pendulum analysis and by uniaxial compression modulus measurements in the rubbery-plateau zone. Further characterization was done by sol gel analysis of the cured samples. It was shown that imidazole does not significantly influence the glass transition temperature and the soluble content of the samples of an excess of amino hydrogen was used. In the case of a stoichiometric ratio of epoxy groups to amino hydrogen and in the case of an epoxy excess, imidazole considerably influences the glass transition temperature of the networks. A dependence of the soluble content of the samples on imidazole concentration used for network synthesis was found mainly in epoxy excess systems.