The unique, environmentally-sound applications of ionic liquids (ILs) are well-known, and include use as green solvents for a variety of chemical processes. Because ILs are stable liquids over a wide temperature range, they offer technological advantages over some chemicals used in their liquid phase, such as plasticizers, where polymer flexibility can be enhanced. Common problems with plasticizers include evaporation and leakage from the surface, instability at high temperatures, lack of lubrication at low temperatures, migration within the polymer, and toxicity. We have addressed couple of these issues using poly(methyl methacrylate), PMMA. Systems studied include bulk PMMA, and PMMA plasticized with butyl methylimidazolium hexafluorophosphate [bmim+][PF6-], hexyl methyl imidazolium hexafluorophosphate [hmim+][PF6-], and a traditional plasticizer, dioctyl phthalate (DOP). Experiments indicate that high temperature stability is improved significantly by replacing DOP with an IL. The effect of IL on glass transition temperature and elastic modulus were also determined. Ionic liquids as plasticizers may revolutionize the usage of flexible polymers at high temperatures, without brittleness or loss of mechanical strength.