Influence of “Free” Ionic Liquid Concentration on the Photopolymerization Kinetics of Ionic Liquid Monomers

In recent years, ionic liquids (ILs) have been explored as materials in a variety of applications.  Although the focus of much of this research has been the use of bulk ionic liquids in electrochemical, separations, and solvent applications, polymers have also been synthesized from ionic liquids containing polymerizable functionalities.  Polymerized ionic liquids (Poly(ILs)) have been explored for use in fields as diverse as catalysis, energy generation, and biological engineering.  However, despite the potential applications of these materials, little research has been completed on the polymerization kinetics of poly(ILs).  Previous research has demonstrated that ionic liquid solvents increase the radical polymerization rate of a variety of vinyl monomers.  In our study, a series of styrene functionalized branched, cyclic, and n-alkyl imidazolium bis(trifluoromethylsulfonyl)imide (Tf₂N) ionic liquids were photopolymerized in the presence of the non-polymerizable ionic liquid [C₂mim][Tf₂N].  Mixtures of varying polymerizable ionic liquid:non-polymerizable ionic liquid molar ratio were polymerized and the conversion of the monomers measured using real-time Fourier transform infrared spectroscopy (FTIR).  These data were used to determine the effects of non-polymerizable ionic liquid solvents on both the monomer conversion and reaction rate of the IL monomers.