• Bulletin of the Korean Chemical Society
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• v.15 no.6
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• pp.419-421
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• 1994

• Bulletin of the Korean Chemical Society
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• v.14 no.4
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• pp.425-427
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• 1993

• Bulletin of the Korean Chemical Society
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• v.19 no.11
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• pp.1153-1155
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• 1998

• Bulletin of the Korean Chemical Society
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• v.12 no.3
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• pp.255-256
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• 1991

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.243.1-243.1
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• 2011

We demonstrate a facile and robust layer-by-layer (LbL) assembly method for the fabrication of nonvolatile resistive switching memory (NRSM) devices based on superparamagnetic nanocomposite multilayers, which allows the highly enhanced magnetic and resistive switching memory properties as well as the dense and homogeneous adsorption of nanoparticles, via nucleophilic substitution reaction (NSR) in nonpolar solvent. Superparamagnetic iron oxide nanoparticles (MP) of about size 12 nm (or 7 nm) synthesized with oleic acid (OA) in nonpolar solvent could be converted into 2-bromo-2-methylpropionic acid (BMPA)-stabilized iron oxide nanoparticles (BMPA-MP) by stabilizer exchange without change of solvent polarity. In addition, bromo groups of BMPA-MP could be connected with highly branched amine groups of poly (amidoamine) dendrimer (PAMA) in ethanol by NSR of between bromo and amine groups. Based on these results, nanocomposite multilayers using LbL assembly could be fabricated in nonpolar solvent by NSR of between BMPA-MP and PAMA without any additional phase transfer of MP for conventional LbL assembly. These resulting superparamagnetic multilayers displayed highly improved magnetic and resistive switching memory properties in comparison with those of multilayers based on water-dispersible MP. Furthermore, NRSM devices, which were fabricated by LbL assembly method under atmospheric conditions, exhibited the outstanding performances such as long-term stability, fast switching speed and high ON/OFF ratio comparable to that of conventional inorganic NRSM devices produced by vacuum deposition.

• Journal of the Korean Chemical Society
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• v.35 no.4
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• pp.362-367
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• 1991

Rates of nucleophilic substitution reaction ([Pd (ONN) Cl] + Y$^-\;{\rightleftharpoons}$ [Pd (ONN)Y] + Cl$^-$ ; Y = SCN$^-$, CN$^-$, N$_3^-$, imidazole, pyridine) have been measured in methanol by spectrophotometric method at various temperatures. A set of nucleophilic reactivity constants, n$_{Pd}^{\circ}$ has been calculated. These values show an order of nucleophilicity CN$^-$ > SCN$^-$ > N$_3^-$ > Imidazole > Pyridine. The enthalpy of activation are small positive values and the entropy of activation are large negative values. From these results, it can be inferred that the nucleophilic substitution reaction proceeds through an associative (A) mechanism.

• Journal of the Korean Chemical Society
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• v.17 no.3
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• pp.174-181
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• 1973

Dichlorodiacetatotitanium(IV) dissolves in alcohols with chemical reaction. Such solvolytic reaction of $TiCl_2(OAc)_2$with various alcohols has been studied by means of solution NMR spectroscopy and chemical analysis of the isolated products. The reaction of $TiCl_2(OAc)_2$ with primary alcohols has shown to be a quantitative two-step ligand substitution process as shown in the following: $TiCl_2(OAc)_2+ROH{\to}TiCl_2(OAc)_2(OR)+AcOH$ $TiCl_2(OAc)_2(OR)+ROH{\to}TiCl_2(OAc)_2+AcOH$The molecular form initially soluble in organic solvents has been found to be the monosubstituted species $TiCl_2(OAc)(OR)$. Alcoholysis with t-butyl alcohol has shown remarkable differences. When the mole ratio of t-butyl alcohol to $TiCl_2(OAc)_2$ is less than 1/2, the following reaction is dominant. $TiCl_2(OAc)_2+t-ButOH{\to}TiCl_2(OAc)_2+t-ButCl$However, at higher mole ratio another substitution process resembling the first step reaction with primary alcohols is competitively accompanied. The reaction with t-butyl alcohol also differs from that with primary alcohols in that only one either of the two chloro-or acetato-ligands in $TiCl_2(OAc)_2$ is subjected to substitution.

• Journal of the Korean Chemical Society
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• v.37 no.2
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• pp.244-248
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• 1993

Nitroalcohols were prepared by a substitution reaction from the corresponding bromoalcohols. The second nitro group was introduced via different methods depending on the carbon chain length. 3,3-Dinitro-1-propanol was obtained by an intramolecular varient of the alkaline nitration method. Whereas 5,5-dinitro-1-pentanol was given by the catalytic oxidative nitration. 3,3-Dinitro-1-propanol and 5,5-dinitro-1-pentanol were converted to 3,3-dinitro-1,6-hexanediol and 4,4-dinitro-1,8-octanediol via Michael reaction with acrolein followed by the reduction of the resulting aldehydes. Acetyl group was a good protecting group for the substitution reaction while THP was for the catalytic oxidative nitration.

• Elastomers and Composites
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• v.43 no.4
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• pp.281-287
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• 2008

Using solid state $^{13}C$ NMR, polybutadiene rubber vulcanizates were qualitatively and quantitatively analyzed. In the filled conventional system of BR vulcanizate accelerated with TBBS, addition to the olefinic double bond and substitution in the $\alpha$ position to the double bond occurred simultaneously. Also the latter $\alpha$ substitution reaction was faster than the former addition reaction at initial reaction time. In addition, it was suggested that double bond-addition-polysulfide structures might be modified into 5-membered and 6-membered cyclic structures in overcure time. These chain modifications were correlated with the decrease in the chemical crosslink density in overcure time.

• Analytical Science and Technology
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• v.17 no.5
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• pp.375-380
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• 2004

Kinetics have been studied by high vacuum and high pressure apparatus under various temperatures and pressures for the nucleophilic substitution reaction. Rate constants, activated parameters and Hammett ${\rho}$-values are determined. The values of ${\Delta}V^{\ddag}$, ${\Delta}{\beta}^{\ddag}$ and ${\Delta}S^{\ddag}$ are all negative. The Hammett ${\rho}$-values are negative for the nucleophile (${\rho}x$) over the pressure range studied. Consequently the rate constant increases as the pressure increases, and some decrease in vacuum. So these reactions proceed in typical $S_N2$ reaction mechanism.