Woo Jin Chung

New Infrared Transmitting Material via Inverse Vulcanization of Elemental Sulfur to Prepare High Refractive Index Polymers

Polymers for IR imaging: The preparation of high refractive index polymers (n = 1.75 to 1.86) via the inverse vulcanization of elemental sulfur is reported. High quality imaging in the near (1.5 μm) and mid-IR (3-5 μm) regions using high refractive index polymeric lenses from these sulfur materials was demonstrated.

Interactions of arenes and thioethers resulting in facilitated oxidation

Synthesis of 6-endo and 6-exomethylthio-2-endoarylbicyclo[2.2.1]heptanes was accomplished stereoselectively. The ionization energies, determined by photoelectron spectroscopy, and electrochemical oxidation potentials, determined by cyclic voltammetry, were lower for the 6-endomethylthio compounds than for their 6-exomethylthio analogues. Calculations supported the notion that facilitation of electron transfer in the 6-endomethylthio compounds results from through-space S...pi interaction.

Synthesis of ferromagnetic polymer coated nanoparticles on multi-gram scale with tunable particle size

The synthesis of ferromagnetic cobalt nanoparticles with polymeric ligands with tunable particle size is reported on multi-gram scales. End-functional polystyrene ligands were prepared via atom transfer radical polymerization. Mechanistic studies on this system were conducted as well as direct comparisons of polymer vs. small molecule ligand effects on nanoparticle formation.

Multiscale Structural Architectures of Novel Sulfur Copolymer Composite Cathodes for High-Energy Density Li-S Batteries Studied by Analytical Multimode STEM Imaging and Tomography

Li-S rechargeable batteries are considered to be a promising light-weight, low-cost, and environmentally friendly candidate for next generation energy storage owing to high theoretical specific capacity of 1,672 mAh/g and high specific energy of 2,567 Wh/kg, which is 5 times that of current Li-ion technology. However, practical use of Li-S batteries remains limited because they suffer from gradual capacity fading caused by insulating properties of sulfur and polysulfide shuttle. Recently, poly(sulfur-random-(1,3diisopropenylbenzene) (poly(S-r-DIB)) copolymers have been introduced for their use as active materials in cathodes for Li-S batteries, and were found to be capable of realizing enhanced capacity retention (1005 mAh/g at 100 cycles) and a five-fold increase in lifetime (over 500 cycles) as compared to conventional sulfur-carbon cathodes [1, 2]. These materials are typically organized in a rough hierarchical 3D architecture which contains multiple components and is quite challenging to understand and characterize.

An unusual epimerization of a thioether

Reaction of 6-exo-methylthio-2-exo-phenylbicyclo[2.2.1]heptan-2-endo-ol with sodium azide and acid afforded the corresponding 2-exo-azide. This azide was reduced and acetylated to give a crystalline derivative whose structure was unequivocally established by X-ray crystallographic analysis. Surprisingly, the isomeric 6-endo-methylthio-2-exo-phenylbicyclo[2.2.1]heptan-2-endo-ol on reaction with sodium azide and acid yielded the same azide as the 6-exo-methylthio analogue. Evidence for the mechanism of thioisomerization is presented.