Glass and sub-glass relaxation changes induced by thermal ageing of epoxy-amine polymer networks – A DMA study

Four epoxy-amine networks were characterized by Dynamical Mechanical Analysis (DMA) and by Dielectric Relaxation Spectroscopy (DRS). The epoxy-amine networks were cured with DGEBA and four aliphatic amine hardeners: three ethylamine hardeners of increasing complexity: ethylene diamine (EDA), diethylene triamine (DETA), triethylene tetramine (TETA), and 4,7,10-Trioxa-1,13-tridecanediamine (TTDA). DGEBA-DETA was aged at 160 °C. Its α relaxation temperature was shown to decrease with time, implying a predominant chain scissions mechanism through the thermal oxidation. DGEBA-DETA and DGEBA-TETA were also shown to display a sub-glassy relaxation made of two components. After ageing at 160 °C, the lowest one around −50 °C, associated to the local motions of hydroxypropyl ether segments, increases in intensity. The second one around 30 °C, with unknown origin but probably from motions in more densely crosslinked areas within the network, disappears with ageing. Those results are discussed regarding the molecular aspects of oxidation.