Thermal, mechanical properties and shape memory performance of a novel phthalide-containing epoxy resins

Abstract

A novel phthalide-containing aromatic amine (PBMI-DDE) was synthesized by Michael addition of 3,3-bis[4-(4-maleimidophenoxy)phenyl]phthalide (PBMI) and 4,4′-diaminodiphenylether (DDE), its chemical structure was confirmed by nuclear magnetic resonance (NMR) spectrometer and Fourier transform infrared (FTIR) spectrometer. A serial of phthalide-containing epoxy resins were prepared with the PBMI-DDE/DDE blends in different molar ratios as curing agents. The cure behavior, thermal and mechanical properties, and shape memory performance of the cured resins were carefully characterized using differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), dynamic mechanical analyses (DMA), universal material testing machine and notched Izod impact test, respectively. DMA and TGA thermograms show the glassy storage modulus and the initial decomposition temperature increase while the rubbery storage modulus and the glass transition temperature are reduced as PBMI-DDE content increases. The investigations of mechanical properties exhibit a complicated trend with increasing PBMI-DDE content, and the epoxy resin with an equal molar ratio of PBMI-DDE/DDE has a maximum mechanical strength. The fracture morphology investigated by scanning electron microscope (SEM) indicates the existence of hole defects in the cured products with higher PBMI-DDE content. The shape memory performance of these fully cured epoxy networks is improved with PBMI-DDE content, and the shape fixity ratio (Rf) and shape recovery ratio (Rr) of the pure PBMI-DDE cured epoxy resins are both lager than 95% with a deformation strain above 12%.