The development of easier, greener, quicker syntheses for complicated and sophisticated materials is a significant driving force behind modern polymer and material chemistry. Economic and environment considerations have brought ionic liquids into the spotlight as an alternative to traditional solvents due to their unique reusability, particularly in the field of polymer chemistry. Interestingly, the use of ionic liquids as polymerization solvents for polypeptides and especially polypeptoids has been rather absent in the literature, despite the fact that these polymerizations are strongly influenced by solvent conditions. We report the use of ionic liquids as a re-usable, extreme low vapor pressure, and tunable solvent for the synthesis of polypeptoids. Specifically, we compared the polymerization potential of several different polypeptoids in various ionic liquids against the best known solvent for these polymerizations: benzonitrile. Here we demonstrate not only the possibility of using ionic liquids as a greener alternative, but because we could tune the hydrophilicity of the solvent without drastically changing the structure and properties (e.g., polarizability, reactivity, or vapor pressure) of the solvent, we could determine a unique feature of this type of polymerizations. Interestingly, we found that benzonitrile and hydrophobic ionic liquids were the best suited for the polymerization of polypeptoids—which are not readily soluble once polymerized. Deeper investigation of this phenomenon by DLS and TEM revealed that these polymerizations likely proceed by a precipitation polymerization mechanism, producing nano- to micrometer sized particles, depending on the polymer and solvent utilized. This work not only gives new application of ionic liquids for use in the polymerization of polypeptoids, but reveals deeper insight to the special polymerization kinetics of polypeptoids systems.

Polymerization of N-NCAs in ionic liquids: Heterophase synthesis of polypeptoids

249th National Meeting (2015)

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