Joint-linker type ionic gels using polymerizable ionic liquid as a crosslinker via thiol-ene click reactions

In this work, we report the synthesis of ion-conductive gels, or ionic gels, via thiol-ene click reactions. The novel gel systems consist of the multifunctional thiol monomers tris[(3-mercaptopropionyloxy)-ethyl]-isocyanurate (TEMPIC), pentaerythritol tetrakis(3-mercaptopropionate) (PEMP), and dipentaerythritol hexakis(3-mercaptopionate) (DPMP) as joint molecules and bifunctional allyl ionic liquid (IL) as a crosslinker. The thiol-ene reaction was carried out in lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) in a propylene carbonate (PC) (1 M) solvent system via a photopolymerization process. The chemical structure and mechanical, thermal, and conductive properties of the gels were investigated using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), compression tests, and impedance spectroscopy, respectively. The mechanical and conductive properties of the ionic gels were found to be largely dependent on the monomer content and functionalities of the joint molecules. TGA revealed good thermal stability of the gels up to 100^◦C. An ionic conductivity of 4.89 mS cm⁻¹ was realized at room temperature (298 K) for low-functional thiol monomers, and a further increase in ionic conductivity was observed with an increase in Li+ ion content and temperature.