Ionic systems in materials research : new materials and processes based on ionic polymerizations and/or ionic liquids

Systems based on ionic interactions are usually related to reversible processes and/or transitory chemical states and, nowadays, they are believed to be key factors for the understanding and for the development of processes in several branches of chemistry and materials research. During the last decades, scientists have developed different approaches for the preparation of new materials and/or substances with outstanding properties based on ionic and other non-covalent interactions. In this thesis, different chemical systems, based on ionic interactions, have been employed for the preparation of different materials and for the development of more efficient synthetic methods in materials research. On the one hand "classical" and emerging applications of ionic interactions are utilized for the preparation of polymeric moieties and other materials, and on the other hand some of the results derived from these single approaches are combined to produce and investigate more complex systems. These systems may find applications in different fields of science and technology: From drug delivery and medical therapies to engineering devices and novel catalytic reactions systems. Thus, this dissertation is divided in three sections. In the first section, the synthetic approach for the well-established anionic polymerization procedure is enhanced by incorporating this technique into a high-throughput work-flow. The development of this experimental approach has allowed and accelerated the systematic synthesis of new block copolymer libraries. Some of the obtained block copolymers were utilized to prepare self-assembled micelles, which were investigated and characterized in detail. Furthermore, the proposed experimental approach was also applied for the development of a new synthetic route to prepare well-defined end-functionalized polymeric architectures bearing supramolecular moieties (e.g., terpyridine groups). In addition, this technique has shown to be a very useful tool for performing detailed kinetic investigations in a short time. Thus, the high-throughput approach was established for one of the most demanding experimental techniques in polymer synthesis. This new tool may help to speed-up research in this field, which will allow a better understanding of structure-property relationships in polymer science. In the second part of the thesis, ionic liquids are investigated as reaction media to carry out polymerizations by different reaction mechanisms. Due to their outstanding chemical and physical stabilities, ionic liquids are proposed as new ionic systems that can offer multiple advantages in polymer synthesis. Thus, it is demonstrated that ionic liquids can be efficiently utilized to perform homogeneous and heterogeneous polymerization reactions. In the homogeneous case, another important ionic polymerization mechanism, cationic ring opening polymerization, was selected as an example for the development of efficient and environmentally-friendly polymerization processes based on ionic liquids as reaction media and microwave irradiation as a heating source. Polymerizations performed in ionic liquids have shown faster reaction rates when compared to other solution polymerization methods, and also allow the synthesis of well-defined and chain extended polymers due to the fact that the investigated polymerization reactions reveal a "living" character. Furthermore, it is shown that the proposed synthetic method is not only limited to one reaction mechanism and can be readily extended to other types of polymerizations, such as free radical processes. Due to the fact that not all monomers and/or polymers are soluble in specific ionic liquids, it is also demonstrated that heterogeneous polymerization processes can be carried out in these substances. For these cases, ionic liquids do not only act as a reaction medium, but they also behave as surfactants to stabilize these heterogeneous systems. This has allowed the synthesis of polymer beads with controlled particle sizes and surface areas. For all the investigated polymerization reactions in ionic liquids, suitable and efficient approaches for the ionic liquid recycling and polymer isolation were developed by the use of water as secondary substance during the separation processes, which entirely avoids the use of volatile organic solvents. In addition, it is also demonstrated that, with the approaches proposed, cleaner and more efficient polymerization processes can be developed due to the known "green" characteristics of ionic liquids (e.g., negligible vapor pressure, negligible flammability, and liquids in a broad range of temperatures) and to the high efficiency of microwave irradiation in the presence of ionic liquids. The proposed environmentally-friendly polymerization processes certainly arise as alternative methods for reducing emissions of harmful volatile organic compounds still widely used throughout the polymer industry and for energy savings. In the last part of the thesis, the materials and/or concepts developed in the first two sections are combined in order to obtain more complex materials and systems. Specifically, amphiphilic block copolymers that were synthesized in the first part of this thesis, or obtained by other methods, are utilized for the preparation of self-assembled micelles in ionic liquids. This has revealed interesting properties due to the fact that these block copolymer micelles, with and without encapsulated guest molecules in their respective core, can be thermo-reversible transferred between two different phases (an aqueous phase and an ionic liquid phase). Furthermore, it is also demonstrated that the investigated block copolymer micelles provide confined environments that protect the encapsulated guest molecules from (sudden) external changes in the surroundings. Finally, the surfactant properties revealed by ionic liquids are utilized for the preparation of composite materials, which is illustrated by two examples: The utilization of ionic liquids has allowed for the efficient and homogeneous dispersion of inorganic materials (e.g. magnetite) into a polymeric matrix. Thus, polymer composites with both magnetic and conductive properties were prepared by an inexpensive method. In addition, this latter concept is also extended to the preparation of composite materials in a liquid state. As a result, novel magnetorheological fluids based on ionic liquids were prepared by dispersing magnetic particles in ionic liquids. The use of ionic liquids has allowed for the preparation of dispersions with low sedimentation rates and magnetorheological fluids with enhanced properties. A combination of the outstanding properties of ionic liquids with the magnetorheological technology led to the fabrication of new and "smart" fluids, which may find applications in several areas of research and technology, such as medical therapies (drug delivery and cancer therapeutic methods), engineering devices (dampers and breaks), as well as accurate transportation and delivery of substances in multiphase biological and chemical systems.