Zum Mechanismus der Polymerkristallisation

Zusammenfassung Auf der Grundlage der Ergebnisse von Röntgenkleinwinkel-Streuexperimenten und elektroenenmikroskopischen Untersuchungen an verzweigtem Polyethylen wird ein neues Modell zum Ablauf des partiellen Kristallisierens und Schmelzens entwickelt. Im Modell wird der Aufbau der Lamellarstruktur als sukzessive Einschubkristallisation beschrieben, die durch die Konzentration an nichtkristallisierfähigen Einheiten in den amorphen Bereichen gesteuert wird. Die Kinetik der Einschubkristallisation läßt sich durch dilatometrische Experimente verfolgen. Aus vergleichenden Röntgenkleinwinkel- und Ramanstreuexperimenten kann auf eine Anreicherung der Cobausteine an den Lamellenoberflächen geschlossen werden.Preprint zur 30. Hauptversammlung der Kolloid-Gesellschaft, 6.–9. Oktober 1981 in Ulm.     

Integrating DNA Photonic Wires into Light‐Harvesting Supramolecular Polymers

An approach combining DNA nanoscaffolds with supramolecular polymers for the efficient and directional propagation of light‐harvesting cascades has been developed. A series of photonic wires with different arrangements of fluorophores in DNA‐organized nanostructures were linked to light‐harvesting supramolecular phenanthrene polymers (SPs) in a self‐assembled fashion. Among them, a light‐harvesting complex (LHC) composed of SPs and a photonic wire of phenanthrene, Cy3, Cy5, and Cy5.5 chromophores reveals a remarkable energy transfer efficiency of 59 %. Stepwise transfer of the excitation energy collected by the light‐harvesting SPs via the intermediate Cy3 and Cy5 chromophores to the final Cy5.5 acceptor proceeds through a Förster resonance energy transfer mechanism. In addition, the light‐harvesting properties are documented by antenna effects ranging from 1.4 up to 23 for different LHCs.     

Helicoidal Patterning of Nanorods with Polymer Ligands

Chiral packing of ligands on the surface of nanoparticles (NPs) is of fundamental and practical importance, as it determines how NPs interact with each other and with the molecular world. Herein, for gold nanorods (NRs) capped with end‐grafted nonchiral polymer ligands, we show a new mechanism of chiral surface patterning. Under poor solvency conditions, a smooth polymer layer segregates into helicoidally organized surface‐pinned micelles (patches). The helicoidal morphology is dictated by the polymer grafting density and the ratio of the polymer ligand length to nanorod radius. Outside this specific parameter space, a range of polymer surface structures was observed, including random, shish‐kebab, and hybrid patches, as well as a smooth polymer layer. We characterize polymer surface morphology by theoretical and experimental state diagrams. The helicoidally organized polymer patches on the NR surface can be used as a template for the helicoidal organization of other NPs, masked synthesis on the NR surface, as well as the exploration of new NP self‐assembly modes.     

A Main‐Group Element Radical Based One‐Dimensional Magnetic Chain

The first main‐group element radical based one‐dimensional magnetic chain ( 1K )_n was realized by one‐electron reduction of the pyridinyl functionalized borane 1 with elemental potassium in THF in the absence of 18‐crown‐6 (18‐c‐6). The electron spin density of ( 1K )_n mainly resides at the boron centers with a considerable contribution from central benzene and pyridine moieties. The spin centers exhibit an antiferromagnetic interaction as demonstrated by magnetic measurements and theoretical calculations. In contrast, the reduction in the presence of 18‐c‐6 afforded the separated radical anion salt 1K(Crown) , in which the potassium cation was trapped by THF and 18‐c‐6 molecules. Further one‐electron reduction of 1K(Crown) and ( 1K )_n led to the diamagnetic monomer and polymer, respectively.