• Polymer(Korea)
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• v.35 no.5
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• pp.444-450
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• 2011

A high molecular weight natural sodium alginate (HMWSAs) was depolymerized by hydrogen peroxide ($H_2O_2$) with ultrasonic irradiation. The effects of the reaction conditions such as reaction temperature, reaction time, hydrogen peroxide concentration and ultrasonic irradiation time on the molecular weights and the end groups of the depolymerized alginates were investigated. It was revealed that depolymerization occurred through the breakage of 1,4-glycosidic bonds of sodium alginate and the formation of formate groups on the main chain under certain conditions. The changes in molecular weight were monitored by GPC-MALS. The molecular weight of 2 wt% alginate solution decreased from 450 to 15.9 kDa for 0.5 hrs at 50 $^{\circ}C$ under an appropriate ultrasonic irradiation. The PDI(polydispersity index)s of the alginate depolymerized in this study were considerably narrow in comparison with those obtained from the other chemical degradation method. The PDIs were in the range of 1.5~2.5 in any reaction conditions employed in this study.

• Polymer(Korea)
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• v.28 no.2
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• pp.170-176
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• 2004

The effect of reaction conditions on the size and size distribution of superparamagnetic iron oxide coated with siloxane was big investigated by using dynamic light scattering. The hydrogen bond between the hydroxyl groups on tile surface of the magnetite and silanol was confirmed by FT-IR. The size of nanoparticles increased with the reaction temperature, but decreased with monomer contents and agitation speeds. There was not a big difference in size of nanoparticles, prepared by different reaction conditions, but its distribution was in the range of 14∼41nm. All samples exhibited the superparamagnetic nature. The magnetic susceptibility of the nanoparticles increased with the reaction temperature while it decreased with the monomer content and agitation speed.

• Analytical Science and Technology
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• v.21 no.5
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• pp.432-437
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• 2008

In this study, polysilanes were synthesized by electroreduction with different monomers such as $CH_3HSiCl_2$, $PhSiCl_3$, $CH_3SiCl_3$ and $(CH_3)_2SiCl_2$ by Mg electrodes under ultrasonic radiation. The effects of monomers and additives (p-dibromobenzene (DBB), naphthalene (NAPH) and anthracene (ANTH)) on the reaction rate were investigated. Polymerization of $PhSiCl_3$ among the four monomers showed the highest rate. p-dibromobenzene (DBB) was proved the most effective additive. Based on the observations, some possible reaction mechanisms of the polymerization were proposed.

• Journal of the Korean Magnetics Society
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• v.13 no.2
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• pp.59-63
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• 2003

Superparamagnetic properties of self-aggregated cobalt nanoparticles in the perfluorinated ion-exchange polymeric membrane (MF-4SK) prepared by ion-exchange and recovery methods were investigated by transmission electron microscopy (TEM) and superconducting quantum interference device (SQUID) magnetometer at various temperatures. Our experimental results show that cobalt nanoparticles in MF-4SK for the concentration of $7.8{\times}10^{19}$ atoms per 1 g of polymer membrane exhibit superparamagnetic properties above the average blocking temperature ($T_{B}$), which is determined to be around 185 K at applied field of 500 Oe. The average particle radius of 4.0 nm achieved from Langevin function fit is in good agreement with TEM observations. This experimental evidence suggests that cobalt nanoparticles in polymer film obey a single domain theory. The results are discussed in the light of current theory for the superparamagnetic behavior of magnetic nanoparticles.

• Journal of Soil and Groundwater Environment
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• v.10 no.5
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• pp.45-51
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• 2005

The sorption/desorption characteristics of phenanthrene on the natural manganese oxide (NMD) were investigated in the presence of phenolic compounds. 4-chlorophenol (4-CP) was effectively oxidized by NMD catalyzed reaction and transformed into humic-like macromolecular compound through inter-or cross-coupling reaction between byproducts. As 4-CP was degraded with time, sorbed amount of phenanthrene on NMD was significantly increased, resulting from the formation of oxidative coupling products. These results imply that NMD can be used for simultaneous treatment of phenolic contaminants and polycyclic aromatic hydrocarbons (PAHs) in soils, sediments, or water. Also, sorbed phenanthrene on NMD in the presence of 4-CP showed high degree of desorption resistance, indicating that sequestration process of phenanthrene was ongoing with time.

• Journal of the Korean Chemical Society
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• v.41 no.2
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• pp.88-97
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• 1997

The silyltriflates$(Ph_{3-n}SiH(OTf)_n)$have been produced by the reaction of triphenylsilane and triflic acid$(CF_3SO_3H)$at low temperature. These highly reactive compounds are a valuable reagent for the synthesis of numerous new functional substituted silane derivatives. The reaction of silyltriflates with alkenyl- and alkynylmagnesium bromide as well as organolithium compounds gave new silanes$Ph_2SiHR(R=\;C(CPh,\;CH=CH_2,\;CH_2CH=CH_2,\; (CH_2)_2CH=CH_2,\;(CH_2)_3CH=CH_2)$in high yields. The hydrosilation of prepared alkenyl- and alkynylsilanesPh_2SiHR$in the presence of a platinum catalyst(Pt/C) at high temperature$(200{\circ}C)$gave carbosilane polymers$((Ph_2SiCH=CPh)_n$and$(Ph_2Si(CH_2)m)n;\;m=2∼4, n{\ge}10)$along with five- and six-membered silaalkane ring compounds derived from intramolecular hydrosilation reactions. All of the prepared compounds are confirmed by NMR, UV, IR and mass spectroscopy as well as elemental analysis.

• Elastomers and Composites
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• v.45 no.2
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• pp.80-86
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• 2010

Carbon nanotubes (CNTs) exhibit excellent mechanical, electrical, and magnetic properties as well as nanometer scale diameter and high aspect ratio, which make them an ideal reinforcing agent for high strength polymer composites. The functionalized CNTs are believed to be very promising in the fields such as preparation of functional and composite materials. CNT-Polymer composites are expected to have good processability characteristics of the polymer and excellent functional properties of the CNTs. However, since CNTs usually form stabilized bundles due to Van der Waals interactions, are extremely difficult to disperse and align in a polymer matrix. The biggest issues in the preparation of CNT-reinforced composites reside in efficient dispersion of CNTs into a polymer matrix, and the alignment and control of the CNTs in the matrix. There are several methods for the dispersion of nanotubes in the polymer matrix such as solution mixing, bulk mixing, melt mixing, in-situ polymerization and chemical functionalization of the carbon nanotubes, etc. These methods and preparation of high performance CNT-polymer composites are described in this review.

• Polymer(Korea)
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• v.36 no.4
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• pp.455-460
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• 2012

Poly(N-isopropylacrylamide) (PNIPAM) hydrogel has been studied as an important drug delivery system due to its volume transition or temperature-responsive swelling properties, whose phase separation temperature is similar to the body temperature. However, because of hydrophilic PNIPAM, hydrophobic drugs are difficult to be uniformly loaded in the networks. Antioxidant alpha-lipoic acid (LA) can be prepared as a polymer(polylipoic acid, PLA) by ring opening polymerization, which is hardly developed as a material due to its low molecular weight and easy depolymerization. To overcome this limitation, a hydrophobic active ingredient, LA was reacted with NIPAM into stable hydrogels. Simple thermal radical reaction successfully resulted in a hydrogel (PNIPAM/PLA), which was confirmed by DSC, FTIR, and Raman spectroscopy. The PNIPAM/PLA showed temperature-responsive properties, and their volume swelling decreased with an increase in lipoic acid content. These hydrogels can carry hydrophobic drugs with PNIPAM and the hydrogels could be useful as final drug delivery systems having lipoic acid as an antioxidant.

• Food Science and Preservation
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• v.6 no.3
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• pp.328-332
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• 1999

This study was investigated pattern changes of tannin isolated from astringent persimmon fruits. The contents of total phenolics and soluble tannins decreased as the maturing and softening of persimmon fruits proceeded. Green and mature persimmon tannins reacted with acetaldehyde. The more contents of tannin increased, the more reactions became. And the reaction of green Persimmon tannin was more active than mature persimmon tannins. But tannin from soft persimmon fruits did not react with acetaldehyde. Tannins were more polymerized during maturing and softening of fruits. So there was a little difference in chromatography of persimmon tannins. Also green and mature persimmon tannins obtained 4 bands respectively after thin layer chromatography analysis. But there was only 2 bands in soft persimmon tannin. As softening of persimmon fruits proceeded, most of tannins reacted with acetaldehyde, so coagulated. Also the component of soluble tannins was changed during softening of persimmon fruits.

• 전기의세계
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• v.13 no.3
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• pp.63-69
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• 1964

한나라의 과학수준이 rocket기술이나 가속기의 출력 energy로서 운운 되었을 때가 있었는데 그때의 기속기는 원자핵 반응을 인공적으로 실험해 보는데 없어서는 안되는 것이기 때문이었다. 2차대전중 원자폭전의 출현을 보게 한 원자로의 발전은 대전후에는 평화적인 이용면에 따르는 응용 분야가 없는 고 energy의 소립자 연구라든지 isotope생산, 고분자화학 및 의료용등에는 대전중에 발전된 잔자기술의 이용으로 더 큰 가속기의 출현이 필요하였다. 특히 이 Electron Accelerator(이하 Linac라고 함)는 높은 고압과 큰 자석을 쓰지 않는 면에서 손쉽게 우리 신변에서 초고압 X선 이상의 효과로 쓸수있게해 주어서 그 이용면은 매우 다급해졌다. 여기서 우리나라의 입장에서 이러한 것을 살펴볼 때 첫째의 radar기술이 충분히 있으면서 이러한 것을 평화적 생산면에서 아직 활용하지 못하고 있으며 한편에서는 외국으로 부터 강력 동위원소를 도입하여 오고 있는데 Linac를 제작하여 여기서 이용하면 이러한 동위원소의 강도 이상의 것을 우리나라 기술로서 제작할 수 있다. 여기서 그 원리와 제작면에 있어서의 문제점 및 국제적인 이용 현황을 소개해 보겠다.