Charge ahead : Moderated ionic bonding for processable polyelectrolyte complex materials

Although materials science has a long history, polymers are a relatively recent addition to the world of materials. Early developments focused on processing or modifying naturally occurring resins and proteins to create what we now recognize as historic ’plastics'. However, demand for more accessible materials drove the development of modern plastics. Over the past 150 years, plastics have transformed industries and everyday life. Yet today, plastics often end up in undesirable places—especially natural and marine environments. While many are recyclable, a fully circular system remains out of reach. Thermosetting plastics are particularly challenging due to their irreversible chemical cross-links. Replacing these with reversible interactions could allow for true recyclability across all polymers. This thesis explores ionic interactions, modified by hydrophobic and steric screening groups, as reversible cross-linkers. We introduce 'compleximers', a new class of polymers that merge the recyclability of thermoplastics with the structural stability of thermosets. Part I presents experimental studies on compleximers, focusing on synthesis, processing, properties, and behavior under heat and plasticization. In Chapter 2, we create compleximers by forming polyelectrolyte complexes from hydrophobically modified polyelectrolytes. Once dried and desalted, these materials can be hot-pressed into plastics without added solvents, and can be reshaped multiple times without loss of mechanical strength. We also study ionic liquids as plasticizers, showing they introduce a glass transition temperature while preserving solvent resistance and network integrity. In Chapter 3, we examine the effects of ionic liquid plasticizers on relaxation dynamics using rheological time-temperature superposition (TTS), fluorescence recovery after photobleaching (FRAP), fluorescence lifetime imaging (FLIM), and broadband dielectric spectroscopy (BDS). We find that plasticizers speed up relaxations but do not significantly alter activation energies. Each method probes distinct processes, from bulk relaxation (rheology) to small-molecule mobility (FRAP, BDS). Chapter 4 introduces a more flexible, fluorine-free compleximer and examines its temperature-dependent modulus in the context of strong glass formers. We reveal a novel inverse relationship between material fragility and relaxation spectrum width, contrary to trends in literature. A new scaling description connects fragility, glass transition steepness, and relaxation spectrum width across various ionic materials.Because experimental variation of structural parameters is limited, Part II uses molecular dynamics simulations to study compleximer architecture. Chapter 5 explores the effects of neutral side-chain length, plasticizer content, and charge density. Reducing charge density or adding neutral chains lowers density and coordination, accelerating dynamics and reducing the glass transition temperature. We also compare the dynamics of ionic liquids, polymerized ionic liquids, and compleximers. Finally, Chapter 6 discusses open scientific challenges, potential applications, and future directions for compleximers. This work highlights a promising route toward recyclable polymeric materials with robust yet reversible network structures.