Confinement of ionic liquid by networked polymers based on multifunctional epoxy resins

Networked polymers confining an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMImTFSI), were prepared by curing a mixture of bisphenol A diglycidyl ether (BADGE) and tetrafunctional epoxy resins with tetraethylenepentamine (TEPA) in the presence of ionic liquid. It was found that addition of the tetrafunctional epoxy resins was inevitable for better ionic liquid confinement. The ionic liquid confinement, ionic conductivity, mechanical strength, and morphology of the materials strongly depended on the ionic liquid content. At a low ionic liquid content (<40 wt %), the material tightly confined the ionic liquid and showed little ionic conductivity with a high Young's modulus, while at a high ionic liquid content (>40 wt %), it did not confine the ionic liquid showing higher ionic conductivity with a low Young's modulus. At a high ionic liquid content (>40 wt %), microphase separation between the ionic liquid and the epoxy networked polymer was observed by scanning electron microscopy (SEM). A transition of the microphase separation from discrete sphere to continuous structure was also observed between 40 wt % and 50 wt % ionic liquid contents. This morphology transition caused a drastic change of the material properties around these ionic liquid contents.