• Journal of the Korean Magnetic Resonance Society
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• v.24 no.4
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• pp.96-103
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• 2020

A new NMR method to monitor solvent-localized NMR signals in the two-phase liquid system is suggested. This method based on intermolecular single-quantum coherence (iSQC). Here, we exploited the feature of the local action of distant dipolar field (DDF) effect in order to filter out specific NMR signals dissolved in different solvents. This solvent specific iSQC spectroscopy was carried out on a model two-phase liquid system (D-glucose in water/palmitic acid in chloroform), and showed solvent-localized NMR signals. We believe our approaches might be useful in metabolic analysis such as two-phase liquid extraction scheme for labile chemical species.

• Bulletin of the Korean Chemical Society
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• v.16 no.3
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• pp.243-248
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• 1995

Single crystal EPR spectra of K12[As2W18O66Cu3(H2O)2]${\cdot}$11H2O exhibit an orientation-dependent fine structure of an S = 3/2 system which is accounted for by the exchange and magnetic dipole interactions among the three Cu2+ ions. The hyperfine structure and the lines from the S = 1/2 manifolds have not been observed. The isotropic exchange parameters determined from the magnetic susceptibility data at 5-300 K are J1 = J2 =-7.8 cm-1. The magnitude of J values suggests that the unpaired electrons on three Cu2+ ions interact through a sequence of six bonds involving two tungsten atoms and three oxygen atoms. The Cu-Cu distance, 4.37 $\AA$, determined from the EPR spectra is considerably smaller than the value from the X-ray crystal structure determination, 4.76 $\pm$ 0.03 $\AA$, indicating that the point-dipole model underestimates the dipolar interaction.

• Bulletin of the Korean Chemical Society
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• v.20 no.3
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• pp.307-313
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• 1999

2,4-Di-(2'-vinyloxyethoxy)benzylidenemalononitrile (la), methyl 2,4-di-(2'-vinyloxyethoxy)benzylidenecyanoacetate (lb), 3,4-di-(2'-vinyloxyethoxy)benzylidene malononitrile (2a), methyl 3,4-di-(2'-vinyloxyethoxy)benzylidenecyanoacetate (2b), 2,5-di-(2'-vinyloxyethoxy)benzylidenemalononitrile (3a), methyl 2,5-di-(2'-vinyloxyethoxy)benzylidenecyanoacetate (3b), 2,3-di-(2'-vinyloxyethoxy)benzylidenemalononitrile (4a), and methyl 2,3-di-(2'-vinyloxyethoxy)benzylidenecyanoacetate (4b) were prepared by the condensation of 2,4-di-(2'-vinyloxyethoxy)benzaldehyde, 3,4-di-(2'-vinyloxyethoxy)benzaldehyde, 2,5-di-(2'-vinyloxyethoxy) benzaldehyde, and 2,3-di-(2'-vinyloxyethoxy)benzaldehyde with malononitrile or methyl cyanoacetate, respectively. Trifunctional divinyl ether monomers 1-4 were polymerized readily with boron trifluoride etherate as a cationic initiator to give optically transparent swelling poly(vinyl ethers) 5-8 havina oxybenzylidenemalononitrile and oxycyanocinnamate, which is presumably effective chromophore for second-order nonlinear optical applications. Polymers 5-8 were not soluble in common organic solvents such as acetone and DMSO due to crosslinking. Polymers 5-8 showed a thermal stability up to 300 ℃ in TGA thermograms, which is acceptable for electrooptic device applications.

• Journal of Industrial and Engineering Chemistry
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• v.67
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• pp.347-357
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• 2018

Steady shear response of a magnetorheological fluid (MRF) system containing porous mono-disperse magnetite ($Fe_3O_4$) spheres synthesized by solvothermal method is demonstrated. In applied magnetic field the interaction between the spherical particles leads to form strong columnar structures enhancing the yield strength and viscosity of the MRFs. The yield strengths of the MRFs also scale up with the concentration of magnetic particles in the fluid. Considering magnetic dipolar interaction between the particles the magneto-mechanical response of the MRFs is explained. Unlike metallic iron particles, the low-density corrosion resistant soft-ferrimagnetic $Fe_3O_4$ spherical particles make our studied MRF system efficient and reliable for shock-mitigation/vibration-isolation applications.

• Journal of the Korean Chemical Society
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• v.24 no.1
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• pp.8-14
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• 1980

Solvolysis rate constants for methylchloroformate, $CH_3O$(CO)Cl, methylthiono-chloroformate, $CH_3O$(CS)Cl, and methylthiolchloroformate, $CH_3S$(CO)Cl, have been determined conductometrically in acetone-water and acetonitrile-water mixtures, and activation parameters, ${\Delta}H^{\neq}$ and ${\Delta}S^{\neq}$, have been derived. Results show that in water-rich regions the order of rate increases as $$CH_3O(CO)Cl while in dipolar aprotic solvent-rich region this order reverses. The plots of log k vs. solvent parameters, Y, $\frac{D-1}{2D+1}$ and log($H_2$) show that the order of rate increase in water-rich region is the results of increase in $S_N1$ character. It is concluded that $CH_3S$(CO)Cl solvolyzes via $S_N1$ mechanism whereas $CH_3O$(CO)Cl reacts via $S_N2$ and $CH_3O$(CS)Cl via intermediate mechanism in water-rich region.

• Applied Chemistry for Engineering
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• v.18 no.1
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• pp.77-83
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• 2007

It is essential that second order nonlinear optical materials have low optical propagation losses in the wavelengths of second harmonic generation for practical applications in waveguides. Three dipolar chromophores substituted with nitro, cyano, and alkyl sulfone as an electron withdrawing group were prepared. The UV-Vis absorption spectra of the cyano and alkylsulfone chromophores showed a blue-shift compared to the nitro chromophore. The introduction of oxadiazole segment in the chromophore structure led to similar spectral shift. The blue-shift can produce low optical loses at second harmonics. The chromophores were successfully attached to a polyimide, yielding side chain polymers. The nonlinear optical property of the prepared optical polymers was determined by measuring electro-optic coefficient at 1.55 mm. The polymers exhibited high glass transition temperature of over $185^{\circ}C$ and thermal stability to $300^{\circ}C$ through differential scanning calorimeter analysis and thermal gravimetric analysis.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1563-1565
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• 1999

Linear and nonliear complex permittivities have been measured for amorphous copolymers of vinylidene cyanide (VDCN) with vinyl acetate (VAc), vinyl propionate (VPr), vinyl benzoate (VBz), styrene (St) and methyl methacrylate (MMA). It is found that the third order permittivity ${\varepsilon}_3$ depends upon frequency according to a function ${\Delta}_{{\varepsilon}_3}/(1+i{\omega}{\tau}_^3)$ while the linear permittivity obeys a Debye function ${\Delta}_{{\varepsilon}_1}/(1+i{\omega}{\tau}_1)$. Experimental results are well fitted by the above predicted functions except at low frequencies where dc conduction dominates. The ${\tau}_1$ and ${\tau}_3$ are nearly equal, and depend upon temperature according to a WLF form. The relaxation strength ${\Delta}_{{\varepsilon}_1}$ depends upon comonomers ranging from $130_{{\varepsilon}_0}$(VAc) to $20{{\varepsilon}_0}$(MMA). The ${\Delta}_{{\varepsilon}_3}$ is negative and depends more strongly upon comonomers. Combined knowledge about linear and nonlinear permittivities predicts very large correlation factors which indicates strongly cooperative dipolar motions in those amorphous copolymers.

• Journal of the Korean Chemical Society
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• v.34 no.5
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• pp.469-475
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• 1990

The reaction of 2,6-dichloroquinoxaline (13) with m-chloroperbenzoic acid gave 2,6-dichloroquinoxaline 4-oxide (14), whose reaction with pyrrolidine or indoline provided 2-substituted 6-chloroquinoxaline 4-oxides (15). The isoxazolo[2,3-a]quinoxalines (16) and pyrrolo[1,2-a]quinoxalines (17) were selectively synthesized from the 2-substituted 6-chloroquinoxaline 4-oxides (15) and dimethyl acetylenedicarboxylate. Moreover, the pyrrolo[1,2-a]quinoxalines (17) were found to be produced by the ring transformation of the isoxazolo[2,3-a]quinoxalines (16).

• Textile Coloration and Finishing
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• v.28 no.2
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• pp.63-69
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• 2016

Poly(butylene terephthalate)(PBT) surface was modified by UV/ozone irradiation and the effect of UV energy on the surface properties of the irradiated PBT films were characterized by the reflectance, surface roughness, contact angles, ESCA, and ATR analyses of the film surface. The surface reflectance, at the short wavelength of visible spectrum of particularly 400nm, decreased with increasing UV energy. And the irradiation roughened the film surface uniformly in the nano scale. The maximum surface roughness increased from 110nm for the unirradiated sample to 303nm at the UV energy of $10.6J/cm^2$. The surface energy of PBT film increased from $50.5mJ/m^2$ for the unirradiated PBT to $58.8mJ/m^2$ at the irradiation of $21.2J/cm^2$. The improvement in hydrophilicity was caused by the introduction of polar groups containing oxygens such as C-O and C=O bonds resulting in higher $O_{1s}/C_{1s}$. The increased dyeability of the modified film to cationic dyes may be resulted from the photochemically introduced anionic and dipolar dyeing sites on the PBT films surfaces.

• Polymer(Korea)
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• v.39 no.1
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• pp.165-168
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• 2015

Thermoresponsive polymers were successfully synthesized by a combination of atom transfer radical polymerization (ATRP) and Cu(I)-catalyzed 1,3-dipolar cycloaddition of azide and alkynes (click chemistry). Poly(2-hydroxyethyl methacrylate) (PHEMA) was synthesized by ATRP, followed by introduction of alkyne groups using pentynoic acid, leading to HEMA-alkyne. Homopolymers having secondary amine groups, tertiary amines with hydroxyethyl and hydroxypropyl groups were synthesized by adding 2-azido-N-ethyl-ethanamine, 2-[(2-azidoethyl)amino]ethanol, and 2-[(2-azidoethyl)amino]propanol, respectively, to the PHEMA-alkyne backbone using click chemistry. Molecular weight (MW), molecular weight distribution (MWD), and click reaction efficiency were determined by gel permeation chromatography (GPC) and $^1H$ NMR spectroscopy. The transmission spectra of the 1.0 wt% aqueous solutions of the resulting polymers at 650 nm were measured as a function of temperature. Results showed that the lower critical solution temperature (LCST) could be easily controlled by the length of the hydroxyalkyl groups.