• Applied Chemistry for Engineering
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• v.22 no.5
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• pp.514-517
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• 2011

Herein, we fabricated magnesium oxalate nanostructures by chemical etching of a magnesium foil in alcoholic solvents containing acidic media. Interestingly, we could obtain magnesium oxalate nanowires in ethanolic oxalic acid. Growth mechanism for magnesium oxalate nanowires was investigated in terms of etching time. Annealing conditions were determined from TGA results. Magnesium oxalate nanowires were converted to magnesium oxide nanowires by thermal treatment and the magnesium oxide nanowires were examined by FE-SEM and FT-IR measurement.

• Journal of the Korean Chemical Society
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• v.37 no.8
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• pp.695-701
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• 1993

Rate constants of solvolysis of 2-thiophenesulfonyl chloride were determined in aqueous binary mixtures with methanol, ethanol, acetone in water and in methanol. These data are interpreted using the equation of Grunwald-Winstein and Kivinen relationship. Also, kinetic solvent isotope effects in water and in methanol and product selectivities in alcohol-water mixtures were determined. Kinetic solvent isotope effect for hydrolysis of 2-thiopenesulfonyl chloride was 2.24 and 1.47 for methanol and water, respectively. Selectivity values for formation of ester relative to acid in ethanol-water mixtures show maximum S value. From kinetic solvent isotope effect in methanol and water, selectivity data in aqueous alcoholic solvents and solvent effects, it is proposed that the reaction channel favoured in low polarity solvents is general-base catalysis and/or is possibly addition elimination (S$_A$N) reaction pathway and in high polarity solvents iS S$_N$2 reaction mechanism.

• Applied Chemistry for Engineering
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• v.16 no.4
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• pp.581-587
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• 2005

In order to obtain a highly purified p-dioxanone (PDX) as monomer of biodegradable polymer, suitable solvent must be selected. The selection was based on the solubility of impurities, and partial layer melt crystallization were carried out under the presence of solvent. The solubility of PDX in various solvents such as ethyl acetate, tetrahydrofuran, acetone, alcohols (methanol, ethanol, 1-propanol, 1-butanol and 1-pentanol) were measured over the temperature range of $-10{\sim}15^{\circ}C$. As solubility parameters, the mixing and dissolution enthalpy between the PDX and the solvents was studied based on empirical equations and the regular solution theory. The solubility and the temperature dependency of the solubility with the solvents of acetone, ethylacetate, and tetrahydrofuran of PDX were shown to have relatively high values compared to the alcohol type solvents. Also, in same alcohols, the smaller molecules and higher polarity gave higher solvency. In partial layer melt crystallization, small amount of ethylacetate selectively dissolved impurities and gave highly purified p-dioxanone, over 99.9% purity.

• Polymer(Korea)
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• v.35 no.5
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• pp.458-466
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• 2011

In the mixed system of supercritical carbon dioxide/organic solvents, poly(vinyl alcohol)(PVA) film of high degree of hydrolysis could be dyed with a dichroic dye of C. I. direct black 22(DB22) and as a result, high durability was obtained. Especially, as a dye dispersant in a supercritical fluid phase, a mixed solvent system of ethylene glycol: dimethyl sulfoxide=4 : 6 weight ratio was investigated. Then the optimum pressure for dyeing could be reduced down to 200 bar. Using this supercritical fluid system, the maximum dyeing appeared as the transmittance of less than 1% and the waste amount was reduced to the level of 1/10. After 500% drawing of this PVA film, both the polarizing efficiency of 94% and the single piece transmittance of 30% were obtained. The limitation of DB22 and further improvements were also discussed.

• The Korean Journal of Rheology
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• v.11 no.1
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• pp.28-33
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• 1999

Introducing boric acid to the polyviny alcohol(PVA) solutions has a profound effect on the rheological properties through crosslinking between hydroxyl groups of PVA. This study investigates the effect of boric acid on the rheological properties of polyvinyl alcohol(PVA)/dimethyl sulfoxide(DMSO)/water systems in the absence of cations. The viscosity of PVA/ DMSO/water systems containing 1 wt.% boric acid was decreased with increasing water content. PVA/DMSO systems containing 1 wt.% boric acid exhibited rheological properties similar to elastic gels by forming crosslinked structures. On the other hand, PVA/water systems containing 1 wt.% boric acid exhibited rheological properties typical of viscous materials. In-corporation of boric acid into PVA/DMSO system caused a notable change in the viscosity of the system, whereas boric acid had little effect on the viscosity of PVA/water system. PVA/DMSO/boric acid system gave the greatest storage modulus among the PVA solution systems. Increasing water level in the mixed solvent of DMSO and water diminished the storage modulus of the systems.

• Journal of the Korean Chemical Society
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• v.27 no.6
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• pp.399-404
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• 1983

Raman spectra for the carbonyl stretching mode of the amides, and amide-solvent systems have been recorded to investigate the effect of alkyl substitutions at the carbonyl carbon and at the nitrogen on the amide hydrogen-bonding. The data have shown that the interaction affinities are in the order of amide-amide > amide-water > amide-alcohol in formamide system, and amide-water > amide-amide > amide-alcohol in acetamide and propionamide systems. The strength of the proton acceptor of the carbonyl oxygen is increased by the presence of alkyl group to the carbonyl carbon and the proton donorcity of the amide is decreased by the alkyl substitution at the nitrogen. The above results are in good agreement with the ab initio SCF MO calculation.

• Journal of Hydrogen and New Energy
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• v.31 no.3
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• pp.276-283
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• 2020

Alcohol-based solvents including ethanol (EtOH) and tert-butyl alcohol (TBA) are investigated instead of isopropanol (IPA), which is a common solvent for polytetrafluoroethylene (PTFE), as an alternative solvent for preparing the catalyst slurry with PTFE binder. As a result, the performance at 0.2 A/㎠ from the single cells from using catalyst slurries based on EtOH and TBA showed very similar value to that from the slurry using IPA, which implies the EtOH and TBA can be used as a solvent for the catalyst slurry. It is also confirmed by the very close values of the total resistance of the membrane electrode assemblies from the slurries using different solvents. In the energy dispersive spectrometry (EDS) image, the shape of crack and dispersion of PTFE are changed according to the vapor pressure of the solvent.

• Journal of the Korean Chemical Society
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• v.29 no.6
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• pp.565-574
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• 1985

The rates of reaction between 4-substituted-2,6-dinitrochlorobenzenes with para-substituted anilines in methanol-acetonitrile mixtures were measured by conductometry. It was observed that the rate constant increases in the order of X = 4-$NO_2 {\gg}4-CN {\gg}4- CF_3$, where X is a substituent in the substrate. The rate constant also increases in the order of Y = p-O$CH_3{\gg}p- CH_3{\gg}H {\gg}p-Cl{\gg}m- NO_2$, where Y is a substituent in the aniline ring. Kinetic studies in the methanol-acetonitrile solvent system with various nucleophiles showed that the N-C bond forming step is making a great contribution to the overall second order rate constant. The electrophilic catalysis by methanol probably consists of the hydrogen bonding between alcoholic hydrogen and leaving chloride in the transition state. The nucleophilic catalysis by methanol may be ascribed to the formation of hydrogen bonds between alcoholic oxygen and hydrogens of amines in the transition state. All these experimental facts are supporting the operation of $S_N$Ar machanism with the second step being the rate determining. This mechanism can be successfully fitted to the PES model.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.10a
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• pp.352-355
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• 2003

비자성이며 비전도성의 물리적 성질을 갖는 자연산 퀄쯔(quartz)와 용암석 스코리아를 대상으로 마그네타이징 처리를 하여 분석하였다. 마그네타이징 처리를 위하여 강력한 기계화학적 분쇄 반응을 시켰으며, 분쇄 반응시 알코올계의 솔벤트를 반응 용매로 사용하였다. 퀄쯔와 스코리아의 마그네타이징 처리에서 비교적 비중이 큰 퀄쯔의 경우와 비중이 작은 스코리아의 경우에도 분쇄된 분말이 물에 뜨는 것을 확인할 수 있으며, 친유성으로 기름에 대한 흡착 성질이 우수함을 확인하였다. 자연산 퀄쯔와 함께 스코리아를 바탕물질로 하여 기계-화학적 반응 기술로 고 분산성 흡착반응에 의한 고분자 물잘 생성을 유도하여 나노복합체를 제조하였다. 반응의 처리조건과 적용과정에 따라서 기계-화학적 반응을 통하여 얻어진 물질은 자기적 성질과 유전체 및 전기적 성질을 동시에 나타낸다. 부착성 융합 복합물질의 특징을 고려하여 시그니토마그네틱스(Segneto-magnetics)로 분류되는 합성분말은 특히 유류성분에 대하여 높은 흡착성을 가지며, 강한 자기적 성질을 띄는 10-50 nm 두께의 하나 또는 그 이상의 이질적 융합 화합물 층이 석영이나 수정체의 표면에 합성되어 특유의 자기, 전기적 성질을 나타낸다.

• Polymer(Korea)
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• v.24 no.5
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• pp.610-620
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• 2000

Vinyl acetate (VAc) was polymerized at 30, 40, and 5$0^{\circ}C$ using 2,2'-azobis (2,4-dimethylvaleronitrile) (ADMVN) and tertiary butyl alcohol (TBA) as the initiator and the solvent, respectively. High molecular weight (HMW) atactic poly(vinyl alcohol) (PVA) was prepared by saponifying the poly(vinyl acetate) (PVAc) synthesized. The effect of polymerization conditions were investigated in terms of conversion, degree of branching for acetyl group of PVAc, and molecular weight of both PVAc and PVA. The polymerization rate of VAc in TBA was proportional to the 0.49th power of ADMVN concentration in good accordance with the theoretical value of 0.5. HMW-PVA with high yield could be obtained successfully, probably due to lower polymerization temperature and decreased chain transfer reaction rate which was achieved by adopting ADMVN and TBA. PYAc having average degree of polymerization (P$_{n}$) of 10000~13000 was obtained at the conversion of 35~70%. Saponification of so prepared PVAc yielded PVA having P$_{n}$ of 2400~6100. The syndiotactic diad content increased with decreasing polymerization temperature and increasing VAc concentration due to a steric hindrance effect of TBA during polymerization.