Thermal, mechanical and conductive properties of imidazolium-containing thiol-ene poly(ionic liquid) networks

A series of imidazolium-based bis(trifluoromethylsulfonyl)imide [NTf2] poly(ionic liquid)s (PILs) were prepared by conducting the solventless thiol-ene 'click' photopolymerization of bisallylimidazolium [NTf2] and pentaerythritol tetrakis(3-mercaptopropionate) (PTMP). The thiol:ene molar ratio was varied in order to examine changes in the thermal, mechanical and conductive properties of the resulting polymer networks. The 1.0:2.0 thiol-ene PIL network exhibited the highest glass transition temperature (T-g of -5.0 degrees C) and storage modulus (E' of 924 MPa at 100 degrees C) values. Temperature-dependent ionic conductivities were found to rely on both the T-g/crosslink density as well as the IL content, with the highest ionic conductivity observed for the 1.0:3.0 thiol-ene PIL network (1.42 x 10(-5) S/cm at 25 degrees C). Application of Vogel-Fulcher-Tammann and Williams-Landel-Ferry theories revealed the impact of both T-g/crosslink density and free ion concentration on temperature-dependent conductivity data, and indicated lower free volumes and fragilities for the thiol-ene networks relative to other non-network PILs. (C) 2016 Elsevier Ltd. All rights reserved.