Kai Pahnke

Consecutive modular ligation as an access route to palladium containing polymers

Polymers with palladium ligating moieties in the lateral chain were synthesized via consecutive CuAAC ligation. An in-depth catalyst screening was performed to optimize the reaction conditions. The obtained polymers, quantitatively loaded with palladium complexes, feature high molar masses of up to Mn = 30 000 g mol−1. The complex formation is underpinned by model complex studies. 2,6-Bis(1-(p-tolyl)-1H-1,2,3-triazol-4-yl)pyridine was used as the model ligand. Reaction of the ligand with [Pd(cod)Cl2] resulted in the corresponding palladium model complex.

Entropy-Driven Selectivity for Chain Scission: Where Macromolecules Cleave

We show that, all other conditions being equal, bond cleavage in the middle of molecules is entropically much more favored than bond cleavage at the end. Multiple experimental and theoretical approaches have been used to study the selectivity for bond cleavage or dissociation in the middle versus the end of both covalent and supramolecular adducts and the extensive implications for other fields of chemistry including, e.g., chain transfer, polymer degradation, and control agent addition are discussed. The observed effects, which are a consequence of the underlying entropic factors, were predicted on the basis of simple theoretical models and demonstrated via high-temperature (HT) NMR spectroscopy of self-assembled supramolecular diblock systems as well as temperature-dependent size-exclusion chromatography (TD SEC) of covalently bonded Diels-Alder step-growth polymers.

Investigation of thermoreversible polymer networks by temperature dependent size exclusion chromatography

Herein we present an advanced analytical protocol for investigating the debonding of thermoreversible polymer networks to enable their in-depth understanding in applications ranging from self-healing materials to 3D additive manufacturing technology. Specifically, the debonding (or de-crosslinking) of a thiocarbonylthio-based hetero Diels-Alder (DA) network is studied in situ by temperature dependent size exclusion chromatography (TD SEC). As the network can be disassembeld at elevated temperatures, its fragments are readily accessible for in-depth analysis by triple-detection TD SEC with refractive index, UV/Vis-and viscosity detection. Critically, the different stages of de-crosslinking can be assessed via the released fragments in terms of their chemical composition and conformation. The results indicate that very broadly distributed and highly branched fragments are released during the initial stages of the disassembly, while more narrowly distributed polymers are expelled at higher degrees of de-crosslinking. In contrast to spectroscopic methods, the introduced chromatography-based approach is potentially applicable to systems of variable chemistries and captures the diverse nature of the de-crosslinking products.

Exploring the Influence of Entropy on Dynamic Macromolecular Ligation

The present thesis reports previously unforeseen effects of physical molecular parameters on reaction entropy and thus chemical equilibria with extensive implications on diverse fields of research via the study of dynamic ligation techniques, especially in the realm of macromolecular chemistry. In addition, a novel, expedient and thermoreversible Diels-Alder linker species for application in, e.g., polymeric materials or ligation chemistry is explored.