Synthesis of a novel siloxane-containing diamine for increasing flexibility of epoxy resins

A new siloxane-containing curing agent (ETSO-DDM) was synthesized from epoxy-terminated siloxane oligomer (ETSO) and 4,4′-diaminodiphenyl methane (DDM) with a hot-melt method. And its structure was characterized by means of FT-IR, ¹H NMR, and ¹³C NMR spectra. The thermal stabilities and the mechanical behaviors of diglycidylether of bisphenol A (DGEBA) epoxy resins cured with ETSO-DDM were examined. The thermal stability factors, such as the initial decomposition temperature (IDT), temperature of maximum rate of degradation (T_max), and decomposition activation energy (E_t), of the DGEBA/ETSO-DDM systems were increased with increasing the ETSO content up to 5 wt% ETSO. The mechanical properties were increased and the internal stress of the cured epoxy resins was decreased as the ETSO content increased. This could be interpreted in terms of the introduction of soft siloxane segment into the epoxy network, which can be attributed to the increasing of the flexibility or decreasing of the internal stress in the DGEBA/ETSO-DDM systems.