• Polymer(Korea)
• /
• v.24 no.2
• /
• pp.159-167
• /
• 2000

The polymethylene-bridged dinuclear half-titanocenes [(CH$_2$)$_{n}$(C$_{5}$ H$_4$)$_2$][TiCl$_3$]$_2$ (n=5(10), 7(11), 9(12)) have been synthesized by treating the distannylated derivatives of the ligands with two equivalents of TiCl$_4$ in toluene. All complexes are characterized by IR, $^1$H NMR, $^{13}$ C NMR and mass spectrometry. In order to examine the catalytic properties of the dinuclear complexes styrene polymerization has been conducted in the presence of MMAO. From the polymerization experiments it was found that ( i ) all the prepared complexes 10-12 produced syndiotactic polystyrenes, ( ii ) the complex 12 holding the longest bridging ligand exhibited the highest activity but produced a polymer having the smallest molecular weight among the polymethylene-bridged dinuclear half-titanocenes. This behavior was attributed to the influence of electron-donating caused by the polymethylene bridge between two active centers as well as the effect of steric congestion around metal center caused by the proximal distance between two active sites.s.

• Polymer(Korea)
• /
• v.30 no.1
• /
• pp.64-69
• /
• 2006

A series of dinuclear half-sandwich titanium complexes with aryloxy substituent at titanium$[(\eta^5-cyclopentadienyl)(aryloxy)TiCl_2]_2[(CH_2)_n]$ (n=3, n=6, n=9) have been successfully synthesized and their styrene polymerization properties have been investigated. All complexes are characterized by $^1H\;NMR,\;^{13}C\;NMR$, elemental analysis, and mass spectrometry. In order to examine the catalytic properties of the dinuclear complexes styrene polymerization has beer conducted in the presence of MMAO. It was found that (i) all the prepared complexes were very effective catalyst for the production of SPS (syndiotactic polystyrene), (ii) the complex with the longest bridge between the two active sites exhibited greatest catalytic activity among the three catalysts, but produced SPS with the smallest molecular weight, (iii) the activities of dinuclear half-titanocens with aryloxy substitution at titanium metal were greater than those of the chloride substituted compounds. These results indicate that not only the nature of the bridge between the two active sites but also the property of substituents at the metal exert a significant influence on the polymerization behaviors of the dinuclear half-titanocene.

• Polymer(Korea)
• /
• v.35 no.1
• /
• pp.35-39
• /
• 2011

In this work, mesoporous carbons (CMK-3) were prepared by a conventional templating method using mesoporous silica (SBA-15) for using catalyst supports in polymer electrolyte membrane fuel cells (PEMFCs). The CMK-3 were chemically activated to obtain high surface area and small pore diameter with different potassium hydroxide (KOH) amounts, i.e., 0, 1, 3, and 4 g as an activating agent. And then Pt-Ru was deposited onto activated CMK-3 (K-CMK-3) by a chemical reduction method. The characteristics of Pt-Ru catalysts deposited onto K-CMK-3 were determined by surface area and pore size analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and inductive coupled plasma-mass spectrometry (ICP-MS). The electrochemical properties of Pt-Ru/K-CMK-3 catalysts were also analyzed by cyclic voltammetry (CV). From the results, the K3g-CMK-3 carbon supports activated with 3 g KOH showed the highest specific surface areas. In addition, the K3g-CMK-3 led to uniform dispersion of Pt-Ru onto K-CMK-3, resulted in the enhancement of elelctro-catalystic activity of Pt-Ru catalysts.

• Advances in nano research
• /
• v.4 no.1
• /
• pp.1-14
• /
• 2016

Superparamagnetic iron oxide nanoparticles (Nps), composed of magnetite, $Fe_3O_4$, or maghemite, ${\gamma}-Fe_2O_3$, core and biocompatible polymer shell, such as dextran or chitozan, have recently found wide applications in magnetic resonance imaging, contrast enhancement and hyperthermia therapy. For different diagnostic and therapeutic applications, current attempt is focusing on the synthesis and biomedical applications of various ferrite Nps, such as $CoFe_2O_4$ and $MnFe_2O_4$, differing from iron oxide Nps in charge, surface chemistry and magnetic properties. This study is focused on the synthesis of manganese ferrite, $MnFe_2O_4$, Nps by most commonly used chemical way pursuing better control of their size, purity and magnetic properties. Co-precipitation syntheses were performed using aqueous alkaline solutions of Mn(II) and Fe(III) salts and NaOH within a wide pH range using various hydrothermal treatment regimes. Different additives, such as citric acid, cysteine, glicine, polyetylene glycol, triethanolamine, chitosan, etc., were tested on purpose to obtain good yield of pure phase and monodispersed Nps with average size of ${\leq}20nm$. Transmission electron microscopy (TEM), X-ray diffraction, energy dispersive X-ray spectroscopy (EDX), $M\ddot{o}ssbauer$ spectroscopy down to cryogenic temperatures, magnetic measurements and inductively coupled plasma mass spectrometry were employed in this study.

• Applied Chemistry for Engineering
• /
• v.28 no.1
• /
• pp.23-28
• /
• 2017

Pyrolysis characteristics of waste plastic films were investigated by using a thermogravimetric analysis and pyrolyzer-gas chromatography/mass spectrometry. Thermogravimetric analysis results revealed that the pyrolysis of waste plastic films can be divided into two distinct reactions; (1) the decomposition reaction of starch at between 200 and $370^{\circ}C$ and (2) that of other plastic polymers such as PS, PP, PE at between 370 and $510^{\circ}C$. The kinetic analysis results obtained by using the revised Ozawa method indicated that the apparent activation energy of the pyrolysis reaction of waste plastic films was also changed dramatically according to the different decomposition reactions of two major waste plastic film components. Py-GC/MS results also revealed that the typical pyrolyzates of each polymer in waste plastic films were levoglucosan (starch), terephthalic acid (PET), styrene monomer, dimer, and trimer (PS), methylated alkenes (PP), and triplet peaks (PE) composed of alkadiene/alkene/alkane. The phthalate, used as a polymer additive, was also detected on the pyrogram of waste plastic films mixture.

• Journal of Ginseng Research
• /
• v.45 no.1
• /
• pp.1-21
• /
• 2021

Panax species have gained numerous attentions because of their various biological effects on cardiovascular, kidney, reproductive diseases known for a long time. Recently, advanced analytical methods including thin layer chromatography, high-performance thin layer chromatography, gas chromatography, high-performance liquid chromatography, ultra-high performance liquid chromatography with tandem ultraviolet, diode array detector, evaporative light scattering detector, and mass detector, two-dimensional high-performance liquid chromatography, high speed counter-current chromatography, high speed centrifugal partition chromatography, micellar electrokinetic chromatography, high-performance anion-exchange chromatography, ambient ionization mass spectrometry, molecularly imprinted polymer, enzyme immunoassay, 1H-NMR, and infrared spectroscopy have been used to identify and evaluate chemical constituents in Panax species. Moreover, Soxhlet extraction, heat reflux extraction, ultrasonic extraction, solid phase extraction, microwave-assisted extraction, pressurized liquid extraction, enzyme-assisted extraction, acceleration solvent extraction, matrix solid phase dispersion extraction, and pulsed electric field are discussed. In this review, a total of 219 articles published from 1980 to 2018 are investigated. Panax species including P. notoginseng, P. quinquefolius, sand P. ginseng in the raw and processed forms from different parts, geographical origins, and growing times are studied. Furthermore, the potential biomarkers are screened through the previous articles. It is expected that the review can provide a fundamental for further studies.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.338-338
• /
• 2013

Monolithic three-dimensional integrated circuits (3D-ICs) 구현 시 bonding 과정에서 발생되는 aluminum (Al) 이나 copper (Cu) 등의 interconnect metal의 확산, 열적 스트레스, 결함의 발생, 도펀트 재분포와 같은 문제들을 피하기 위해서는 저온 공정이 필수적이다. 지금까지는 polymer 기반의 bonding이나 Cu/Cu와 같은 metal 기반의 bonding 등과 같은 저온 bonding 방법이 연구되어 왔다. 그러나 이와 같은 bonding 공정들은 공정 시 void와 같은 문제가 발생하거나 공정을 위한 특수한 장비가 필수적이다. 반면, 두 물질의 합금을 이용해 녹는점을 낮추는 eutectic bonding 공정은 저온에서 공정이 가능할 뿐만 아니라 void의 발생 없이 강한 bonding 강도를 얻을 수 있다. Aluminum-germanium (Al-Ge) 및 aluminum-indium (Al-In) 등의 조합이 eutectic bonding에 이용되어 각각 $424^{\circ}C$ 및 $454^{\circ}C$의 저온 공정을 성취하였으나 여전히 $400^{\circ}C$이상의 eutectic 온도로 인해 3D-ICs의 구현 시에는 적용이 불가능하다. 이러한 metal 조합들에 비해 indium (In)과 tin (Sn)은 각각 $156^{\circ}C$ 및 $232^{\circ}C$로 굉장히 낮은 녹는점을 가지고 있기 때문에 In-Sn 조합은 약 $120^{\circ}C$ 정도의 상당히 낮은eutectic 온도를 갖는다. 따라서 본 연구팀은 In-Sn 조합을 이용하여 $200^{\circ}C$ 이하에서monolithic 3D-IC 구현 시 사용될 eutectic bonding 공정을 개발하였다. 100 nm SiO2가 증착된 Si wafer 위에 50 nm Ti 및 410 nm In을 증착하고, 다른Si wafer 위에 50 nm Ti 및 500 nm Sn을 증착하였다. Ti는 adhesion 향상 및 diffusion barrier 역할을 위해 증착되었다. In과 Sn의 두께는 binary phase diagram을 통해 In-Sn의 eutectic 온도인 $120^{\circ}C$ 지점의 조성 비율인 48 at% Sn과 52 at% In에 해당되는 410 nm (In) 그리고 500 nm (Sn)로 결정되었다. Bonding은 Tbon-100 장비를 이용하여 $140^{\circ}C$, $170^{\circ}C$ 그리고 $200^{\circ}C$에서 2,000 N의 압력으로 진행되었으며 각각의 샘플들은 scanning electron microscope (SEM)을 통해 확인된 후, 접합 강도 테스트를 진행하였다. 추가로 bonding 층의 In 및 Sn 분포를 확인하기 위하여 Si wafer 위에 Ti/In/Sn/Ti를 차례로 증착시킨 뒤 bonding 조건과 같은 온도에서 열처리하고secondary ion mass spectrometry (SIMS) profile 분석을 시행하였다. 결론적으로 본 연구를 통하여 충분히 높은 접합 강도를 갖는 In-Sn eutectic bonding 공정을 $140^{\circ}C$의 낮은 공정온도에서 성공적으로 개발하였다.

• Clean Technology
• /
• v.17 no.2
• /
• pp.124-133
• /
• 2011

In addition to six substances regulated in EU RoHS including lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE), priority substances are identified in new RoHS II as hexabromocyclododecane (HBCDD), dibutyl phthalate (DBP), butyl benzyl phthalate (BBP) and diethylhexyl phthalate (DEHP). In this study, 20 plastic samples were collected from 12 domestic electrotechnical companies and levels of four restricted substances were determined by gas chromatography-mass spectrometry, Among 20 parts that compose washer, refrigerator or microwave oven, HBCDD was detected in three samples of NBR material with the amount of 42~381 mg/kg while DBP and BBP was not detected in any samples collected respectively, implying that these substance may not be used widely in plastic materials for EEE. However, DEHP was detected in all samples of NBR, PP, PBT, EPDM and PVC materials with the amount of 42 up to 59,400 mg/kg that exceeds the limit value of 0.1 wt% (1,000 mg/kg). Presence of a restricted substance in polymer material makes a great negative influence on a number of final product. To cope with coming RoHS II as well as REACH, action not to use DEHP in plastic material or the relevant notification in case of REACH seems to be needed. Screening test of Arsenic compounds such as diarsenic pentaoxide, diarsenic trioxide, lead hydrogen arsenate, triethyl arsenate that are included in REACH SVHC was done by ICP measurement Arsenium was detected in four samples made of NBR and PBT materials in the level of 15~700 mg/kg. By considering the screening method used in this study, the amount of arsenium compounds in the thermistor made of PBT material has a high chance of exceeding the regulated limit value.