Influence of counteranion and humidity on the thermal, mechanical and conductive properties of covalently crosslinked ionenes

Abstract

Thiol-ene photopolymerization was used to generate a series of covalently crosslinked, imidazolium-containing ionene networks. A variety of counteranions were chosen so as to investigate the influence of size and basicity on the thermal, mechanical and conductive properties of the resulting networks. Anhydrous conductivities at 20 °C were found to be on the order of 10−6 to 10−10 S/cm and correlated to some degree with Tg; however, Tg-normalization of the curves indicated that this relationship between polymer structure and conductivity was more complex. VFT fitting, along with free ion concentration and ion mobility data, were investigated in order to provide additional insight. Also of interest in this study was the influence of humidity on ionic conductivity. Hydrophilic networks with anions such as [Cl], [NO3] or [OMs] were found to exhibit 3- to 5-orders of magnitude enhancement in ionic conductivity (up to 10−3 S/cm) when the relative humidity was increased to 70% while the more hydrophobic networks ([PF6] and [NTf2]) were not influenced. Further experimentation (water uptake, DSC) indicated that the observed enhancements in conductivity were likely due to a combination of plasticization and water-assisted ion transport.