Ionogels by thiol-ene photopolymerization in ionic liquids: Formation, morphology and properties

A new class of ionogels with a thiol-ene matrix showing a phase-separated morphology was obtained from triallyl isocyanurate and trimethylolpropane tris(3-mercaptopropionate) via a photo-induced polymerization in ionic liquids (ILs). The compatibility between the polymer matrix and ILs decreased with the decrease of the Kamlet-Taft α parameter of the solvent; polymerization was faster in ILs with higher values of the Kamlet-Taft β parameter. The matrix had a “colloidal gel” structure built of interconnected microspheres forming a 3-dimensional network percolating throughout the IL. For the first time, spherical poly(thiol-ene) particles were obtained in ILs; the size of the particles depended on the monomer concentration and the IL ability to stabilize the colloidal microspheres through H bonding. The low solubility of ILs in the matrix along with sufficiently strong interactions matrix/IL resulted in the appearance of anti-plasticization effect. The obtained ionogels had high ionic conductivity (∼2.6 ÷ ∼ 7.0 mS cm−1 at 25 °C) and very high relative conductivity (higher than the highest possible values resulting from the IL content); this allows the majority of the IL conductivity in the ionogel to be retained.