Molecular Design of High-Performance Imidazolium Ionenes as Gas Separation Membranes and 3D Printing Materials
This dissertation details the development and performance of a library of imidazolium ionenes for advanced engineering applications, with an emphasis on membrane-based gas separations and additive manufacturing. Several distinct sets of high-performance ionenes, polymers which contain ionic groups along the backbone chain rather than as pendants, were methodically designed and synthesized. These materials combine structural features commonly associated with state-of-the-art gas-separation membranes with chemical functionalities associated with high-performance engineering polymers. These functional features are spaced by incorporated ionic groups along the main chain, specifically imidazolium cations paired with fluorinated, delocalized anions. The modular synthetic methods and diverse processability of these new ionenes demonstrate that the rational design of materials can lead to enhanced performance and unique properties and behaviors. Through variation of substituents, connectivity along the backbone, and the sequence of functional and ionic segments, this work demonstrates the expansive opportunities for incorporating, distributing, and alternating structural features. These ionenes possess excellent thermal and mechanical properties, while the tailorability and synthetic modularity ionenes provide access to an array of interesting behaviors and molecular architectures. These ionic polymers materials exhibit self-assembly and local structuring when impregnated with “free” imidazolium-based ionic liquids (IL) or multivalent organic salts, which contributes additional tunability and alters intermolecular interactions in the ionene matrix. These HP-ionenes and IL composites were thoroughly characterized to develop structure-property relationships and to understand the coordination between the dispersed, discrete additives and the polymeric ionene matrix. Using the information gathered from characterization of these ionenes and IL composites, the specific suitability of processing techniques for each series of functional imidazolium ionenes was explored, yielding applied studies of these advanced materials as films/coatings, fibers, 3D printing resins, and self-healing elastomers.