Evolution of hybrid guanidine ligands: influence on the catalyst and performance in copper complex mediated atom transfer radical polymerisation
| Autor: | Kröckert, Konstantin Wilhelm |
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| Jazyk: | angličtina |
| Rok vydání: | 2023 |
| Předmět: | |
| DOI: | 10.18154/rwth-2023-06060 |
| Popis: | Dissertation, RWTH Aachen University, 2023; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2023). = Dissertation, RWTH Aachen University, 2023 In the last two decades, the design of N-donor ligands was optimised to improve copper complexes as atom transfer radical polymerisation (ATRP) catalysts. It has been shown that this is the key to lowering the catalyst loading and enhancing the polymerisation control. This allows the preparation of tailored polymers for high-value applications such as coatings and adhesives. In this thesis, a series of bidentate and tetradentate guanidine ligands was prepared to investigate the influence of several structural features on the ATRP catalyst activity. Therefore, structure-activity correlations and highly active systems are presented. As bidentate ligands, guanidine-pyridinyl, and guanidine-quinolinyl systems have been studied. Dimethylamine substituents were introduced at the 4-positions of the aromatic systems to increase their donor strength. The flexibility in the backbone differs between these systems, and the guanidine moieties were varied (tetramethylguanidine (TMG) and dimethylethylguanidine (DMEG)). The molecular structures of the copper complexes were investigated in the solid state as well as in solution studies, and the redox potentials, which correlate to the catalytic activities, were determined. The activities of these systems increase for dimethylamine substituted relative to unsubstituted ligands, for TMG vs. DMEG, and pyridinyl vs. quinolinyl moieties. These changes in the ligand design affect the positions of coordinating N-donors and lead to elongated Cu−Br bond lengths. Thus, a relation between the ligand design, the coordination sphere around the copper, and the catalyst activity was found. The N donor ligand TMGm4NMe2py combines all activity-increasing features, leading to the most active ATRP catalyst based on bidentate systems. Moreover, synthetic routes to the new tetradentate ligands TMG-4NMe2uns-penp and TMG-4NMe2apme were developed. Molecular structures of copper complexes based on the comparable ligands TMG-4NMe2uns-penp, TMG-uns-penp, and TMG3tren were discussed, and the corresponding potentials of the redox couples were determined. Dimethylamine substitution leads to a higher catalyst activity. Furthermore, the results indicate that TMG moieties in tripodal ligand systems potentially induce a faster exchange within the ATRP equilibrium than traditionally used ligands. It derives from a larger halide distance that induces a better stabilisation of the required copper(I) activator species and an easier cleavable Cu−Br bond of the copper(II) deactivator species. With these catalysts, controlled conditions for the standard ATRP of styrene were found. Moreover, the highly active systems are suitable as catalysts for continuous regeneration ATRP techniques. Published by RWTH Aachen University, Aachen |
| Databáze: | OpenAIRE |
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