Effects of network segment structure on the phase homogeneity of crosslinked poly(ethylene oxide)/epoxy networks

Differential scanning calorimetry (d.s.c.), optical microscopy and scanning electron microscopy (OM and SEM), and Fourier Transform infrared (FTi.r.) studies have been performed to demonstrate several cases of cured poly(ethylene oxide)/(diglycidylether of bisphenol-A) epoxy networks. To evaluate effects of structural change of the crosslinked epoxy segments on the morphology of polymer/epoxy networks, three different types of hardening agents were used. An interesting miscible phase was observed in aromatic amine-cured PEO/DGEBA and anhydride-cured PEO/DGEBA. Structurally, it can be viewed that the PEO chains interpenetrate with entanglement into the crosslinked epoxy network. Thermodynamically, the glass transition results indicate that the PEO chains also intimately mingle with the epoxy-DDS network chain segments to achieve a homogeneous solid state. By comparison, aliphatic amine curing led to phase separation. Apparently, different structure of hardeners led to different chain segments of cured epoxy, which in turn could influence the ultimate phase morphology of cured PEO/epoxy solids. For the miscible polymer/epoxy networks, the cure temperature (thus cure kinetic rate) was found to exert no effects on influencing phase homogeneity. Factors controlling homogeneity of polymer/epoxy after cure were studied and discussed in this report.