(526i) Effect of Molecular Architecture on Photopolymerization and Gelation of Coordinated Ionic Liquids

Coordinated ionic liquids (ILs) containing reactive sites provide a tunable medium for bulk polymerization and network formation. In contrast to traditional ILs, which are composed of an organic cation and an anion, coordinated ILs can be formed from uncharged ligands coordinated with metal cations and weakly coordinated anions. When the metal-ligand coordinated cation contains a polymerizable group (such as a vinyl or acryloyl moiety), polymerized ILs can be formed that contain a coordinated IL species in each repeat unit. In this study, dynamic rheology and real-time Fourier transform infrared (RT-FTIR) spectroscopy are used to monitor the in situ photopolymerization and gelation of coordinated ILs containing varying molar ratios of substituted vinylimidazoles (including 1-vinylimidazole, 2-methyl-1-vinylimidazole, 2-phenyl-1-vinylimidazole, and 2,4,5-trimethyl-1-vinylimidazole) with both monovalent and divalent metal bistriflimide salts (such as LiTf₂N, KTf₂N, and Ca(Tf₂N)₂). We demonstrate that monomer substitution, choice of metal cation, and concentration of bistriflimide salt all affect the coordinated IL viscosities and photorheological response when exposed to varying lengths and intensities of UV light. The approximate polymer content produced under each set of exposure conditions is obtained through measures of monomer conversion using parallel RT-FTIR experiments. We observe that some samples undergo simultaneous polymerization and gelation, which can be attributed to metal ion coordination with imidazole pendant groups on neighboring polymer chains forming physical crosslinks. The gel time, gel strength, and bistriflimide salt concentration necessary for gelation are also shown to be directly affected by vinylimidazole substitution and selection of metal cation. Our results seek to demonstrate that coordinated ILs provide a highly tunable and largely unexplored chemical space for light-induced synthesis of polymerized ILs.