Hyun Min Jung

One-pot synthesis of diarylalkynes using palladium-catalyzed sonogashira reaction and decarboxylative coupling of sp carbon and sp2 carbon.

Decarboxylative coupling of sp-sp2 carbons is possible by palladium catalyst. Employing propiolic acid (1) as a difunctional alkyne, and using the consecutive reactions of the Sonogashira reaction and the decarboxylative coupling, unsymmetrically substituted diaryl alkynes were obtained in moderate to good yield.

Enzymatic resolution of secondary alcohols coupled with ruthenium-catalyzed racemization without hydrogen mediator

Abstract ( η 5 -Indenyl)RuCl(PPh 3 ) 2 was found to catalyze the racemization of secondary alcohols in the presence of triethylamine and oxygen. Unlike previously reported metal-catalyzed racemizations, ketones were not required as hydrogen mediators in our process. The Ru-catalyzed racemization was coupled with enzymatic acetylation for the dynamic kinetic resolution of secondary alcohols to give chiral acetates in good yields (60–98%) with high enantioselectivities (82–99% ee ).

Enhanced Catalytic Performance by Zirconium Phosphate‐Modified SiO2‐Supported RuCo Catalyst for Fischer–Tropsch Synthesis

Our zirconium phosphate (ZrP)‐promoted Ru/Co/ZrP/SiO2 catalyst reveals a high catalytic activity and stability during Fischer–Tropsch synthesis. Surface modification with ZrP on SiO2 support with an appropriate amount of phosphorous component prevents cobalt particle aggregation and enhances its stability. These positive effects of ZrP are mainly induced by the spatial confinement of cobalt particles in a thermally stable ZrP matrix, and the catalytic performance was greatly improved when the P/(Zr+P) molar ratio was 0.134 on the CoZrP(0.5) catalyst.

Fluoropropane sultone as an SEI-forming additive that outperforms vinylene carbonate

Vinylene carbonate (VC) has been the best performing solid electrolyte interphase (SEI) additive for the current lithium-ion batteries (LIBs). However, it is also true that the current LIB technology is being stagnated by the limit set by VC. This study introduces 3-fluoro-1,3-propane sultone (FPS) as a novel SEI additive to replace VC and another popular SEI additive, 1,3-propane sultone (PS). Both density functional calculations and electrochemical experiments confirm that the presence of an electron withdrawing fluorine group is favourable in terms of anodic stability and SEI forming ability. In the cyclability of LiCoO2/graphite cells over a wide temperature range (25–60 °C), FPS exhibits remarkable enhancement compared with PS, and is even superior to VC. During elevated temperature (90 °C) storage of the cells, VC suffers from severe swelling, whereas FPS causes little thermal degradation. Considering the high anodic stability, the excellent cyclability, and the good thermal stability, FPS is an outstanding SEI additive that can expand the performance boundary of the current LIBs.

Carbon nanotubes produced by tungsten-based catalyst using vapor phase deposition method

Abstract We have demonstrated that W-based catalysts can produce carbon nanotubes (CNTs) effectively. Well-aligned, high-purity CNTs were synthesized using the catalytic reaction of C 2 H 2 and W(CO) 6 mixtures. The CNTs had a multiwalled structure with a hollow inside. The graphite sheets of CNTs were highly crystalline but the outmost graphite sheets were defective.

Facile fabrication of superhydrophobic coatings with polyimide particles using a reactive electrospraying process

A facile method for polyimide (PI) coating with enhanced hydrophobicity through the deposition of morphology controlled PI particles is presented. An electrospraying process combined with in situ imidization was employed in the fabrication of the PI particles for controllable morphologies as well as hydrophobic multilayered films. We confirmed that in situ imidization accompanying evaporation of the solvent affected the surface morphology of the PI particles during the reactive electrospraying process. The competition of in situ imidization and solvent evaporation in the heating process induces not only the formation of a dimple structure but also the formation of a hollow structure, which was affected by the droplet size. The multilayered film produced by deposition of the PI particles had a microstructured surface with spherical protrusion, micro-dimples, and micro-channels. The multilayered film of PI particles exhibited a hydrophobic surface with water contact angle of 151° due to the microstructured surface of PI coating which was simply but effectively generated by reactive electrospray technique.

Enhanced dielectric properties of polyimide/BaTiO3 nanocomposite by embedding the polypyrrole@polyimide core-shell nanoparticles

A three-phase polymer composite with a ferroelectric phase (BaTiO3) and conductive core-shell polypyrrole@ polyimide (PPy@PI) nanoparticles embedded in a polyimide (PI) matrix was prepared by using a simple direct mixing and solution casting process. PPy@PI nanoparticles as the conductive filler were synthesized to obtain homogeneous dispersion in the PI matrix. The dependence of the dielectric behavior on the BaTiO3 and PPy@PI contents was studied over a wide frequency range from 10 kHz to 1 MHz. The incorporation of low loading levels of PPy@PI nanoparticles to the PI/BaTiO3 system led to a significant enhancement in the dielectric constant with suppressed loss. The dielectric constant (Dk) of the PI/BaTiO3/PPy@PI (25/75/5) hybrid was 58.53 at 10 kHz, i.e., three times higher than that of the PI/BaTiO3 (25/75) nanocomposite without PPy@PI. The fairly improved dielectric properties were due to the synergistic enhancement of the ferroelectric ceramic filler, BaTiO3, and conductive filler, PPy@PI nanoparticles, as well as due to homogeneous dispersion. Such polymer composites have the potential for use in fabricating embedded capacitors, and specimens with various shapes can be easily obtained owing to the flexibility of the nanocomposite.

Amide-based oligomers for low-viscosity composites of polyamide 66

Melt viscosity control of polyamides is an important issue concerning polymer processing and quality composites which are directly influenced by the melt viscosity in extrusion and injection molding processes. In this work, a series of linear and cyclic PA6 (nylon6), PA46 (nylon46), and PA66 (nylon66)-based amide oligomers consisting of <10 repeat units are prepared. The melt viscosities of the composites of each oligomer in a PA66 matrix are investigated. The linear oligomers have a larger viscosity-decreasing effect than cyclic oligomers containing the same repeat unit. Linear PA6 and PA46-based oligomers show a greater melt viscosity reduction than PA66-based ones, especially in PA6-based linear oligomer (A6-L), which shows a reduction of >30%. This result suggests that proper hydrogen bonding mismatching in the polymer chain network plays an important role for lowering viscosity. A6-L/PA66 composites impregnated with 40 wt% glass fiber show a twofold increase in the melt flow index while maintaining their mechanical strengths.