• Elastomers and Composites
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• v.40 no.3
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• pp.212-221
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• 2005

Polyurethanes containing mesogen unit (MPU-6) were prepared from 4,4'-diphenylmethane diisocyanate (MDI) and 4,4'-bis(6-hydroxy hexoxy)biphenyl (BP-6) having flexible chain composed of 6 carbons. Intrinsic viscosities of MPU-6s were in the range of $0.23{\sim}0.56 dL/g$. The mesomorphic behaviors of MPU-6 were observed in X-ray and polarizing microscopy analysis. However, MPU-6s demonstrated a 'virtual liquid crystal' behavior, which did not exhibit mesophase on slow heating and slow cooling. MPU-6 having lower molecular weight exhibited higher crystallization rate and melting crystallization temperature due to increased mobility of polymer chains. The increased mobility of polymer chains facilitate the orientation of mesogen units that may act as a nucleating agent.

• Korean Chemical Engineering Research
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• v.54 no.2
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• pp.268-273
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• 2016

To improve mechanical strength of carbon foams, the carbon black (CB) added carbon foams were fabricated by impregnating different contents of carbon black (CB) and mesophase pitch using polyvinyl alcohol (PVA) solution into polyurethane foam and being followed by heat treatment. The cell wall-thicknesses of carbon foams were controlled by adding amounts of CB, and it was confirmed that the compressive strength of carbon foams was increased as increasing cell wall-thickness. The compressive strength had the highest value of $0.22{\pm}0.05MPa$ with the highest bulk density of $0.44g/cm^3$ when adding 5 wt% CB in carbon foam. However, the thermal conductivity was decreased by adding CB in carbon foam. The results indicated that the thermal conductivities of carbon foams were reduced by increased interlayer spacing ($d_{002}$) with the addition of CB in carbon foams.

• Polymer(Korea)
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• v.28 no.1
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• pp.41-50
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• 2004

A new hydroxypropyl chitosan capable of forming a thermotropic liquid crystalline phase and two kinds of derivatives based on the hydroxypropyl chitosan (6-cholesteryloxycarbonylpentoxypropyl) chitosans (CHPCTs) and acrylic acid esters of CHPCT (CHPCTEs) were synthesized. The crosslinked films with liquid crystalline order were also prepared by photocrosslinking CHPCTE in mesophase. The liquid crystalline properties for all the samples and the swelling behavior of the crosslinked samples in acetone were investigated. In contrast with the hydroxypropyl chitosan, all the uncrosslinked cholesteryl-bearing samples farmed monotropic cholesteric phases with left-handed helicoidal structures and exhibited reflection colors over the full cholesteric range. This is the first report of a thermotropic cholesteric liquid crystalline chitosan derivative with reflection bands in the visible region. Both the optical pitches (λ$\_$m/'S) of CHPCT and CHPCTE decrease with temperature or with cholesteryl content at a given temperature. However, the λ$\_$m/ of CHPCT was larger than that of CHPCTE at the same temperature and at the same cholesteryl content. All the crosslinked samples did not display reflection colors, indicating that the cholesteric structure of CHPCTE significantly changes upon crosslinking. The two-dimentional anisotropic swelling characteristic of liquid crystalline networks was observed for all the crosslinked samples.

• Polymer(Korea)
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• v.30 no.4
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• pp.338-349
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• 2006

Fully or nearly fully(8-cholesteryloxycarbonyl)heptanoated polysaccharide derivatives were synthesized by reacting cellulose, amylose, chitosan, chitin, alginic acid, pullulan or amylopectin with (8-cholesteryloxycarbonyl)heptanoyl chloride (CH8C), and their thermotropic liquid crystalline behaviors were investigated. Like in the case of CH8C, all the polysaccharide derivatives formed monotropic cholesteric phases with left-handed helicoidal structures whose optical pitches $({\lambda_m}'s)$ decrease with increasing temperature. Amylopectin derivative also formed a monotropic cholesteric phase with lefthanded helicoidal structures but, in contrast with the other derivatives, did not display reflection colors over the full cholesteric range, suggesting that the helicoidal twisting power of the cholesteryl group highly depends on the branched structure in amylopectin. The thermal stability and degree of order in the mesophase, the magnitude of ${\lambda}_m$ at the same temperature, and the temperature dependence of the ${\lambda}_m$ observed for polysaccharide derivatives were entirely different from those reported for the polymers in which the cholesteryl groups are attached to flexible or semiflexible backbones through flexible spacers. The results were discussed in terms of the difference in the chemical structures of the main and side chains and flexibility of the main chain.

• Polymer(Korea)
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• v.31 no.1
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• pp.58-67
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• 2007

Fully cholesteryloxycarbonated and (8-cholesteryloxycarbonyl) heptanoated disaccharide derivatives were synthesized by reacting cellobiose, maltose, and lactose with cholesteryl chloroformate or 8- cholesteryloxycarbonylheptanoyl chloride, and their thermotropic liquid crystalline properties were investigated. All the cholesteryloxycarbonated derivatives (CH1DSs) formed enantiotropic cholesteric phases, whereas all the (8-cholesteryloxycarbonyl) heptanoated derivatives (CH8DSs) exhibited monotropic cholesteric phases with left-handed helicoidal structures whose optical pitches (${\lambda}m's$) decrease with increasing temperature. All the CH1DSs, contrast with the CH8DSs, did not display reflection colors over the full cholesteric range, suggesting that the helicoidal twisting power of the cholesteryl group highly depends on the length of the spacer joining the cholesteryl group to the disaccharide chain. The thermal stability and degree of order in the mesophase and the temperature dependence of the ${\lambda}m$ observed for EH8DSs were entirely different from those reported for the cholesterol-bearing dimers and triplet and the (8-cholesteryloxycarbonyl) heptanoated polysaccharide derivatives. The results were discussed in terms of the difference in the number of the mesogenic units per mole of repeating unit and the flexibility of the main chain.

• Polymer(Korea)
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• v.31 no.4
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• pp.356-367
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• 2007

Three kinds of amylose derivatives such as: cholesteryloxycarbonated amyloses(CAMs) with degree of esterification(DE) ranging from 1.8 to 3, (6-cholesteryloxycarbonyl)pentanoated amyloses(PAMs) with DE ranging from 0.3 to 3, and fully cholesteryloxycarbonated PAMs(CPAMs) were synthesized, and their thermotropic liquid crystalline properties were investigated. CAMs with $DE{\geq}2.6$, PAM with DE=1.6 and all the CPAMs formed enantiotropic cholesteric phases, whereas PAM with $DE{\geq}2.2$ exhibited monotropic cholesteric phases. PAM with $DE{\geq}2.2$ and CPAMs with (6-cholesteryloxycarbonyl)pentanoyl DE (DS) more than 1.0 formed cholesteric phases with left-handed helical structures whose optical pitches (${\lambda}_{m'}s$) decrease with increasing temperature. However, the ${\lambda}_{m'}s$ of these samples decreased with increasing DS at the same temperature. On the other hand, CAMs, PAM with DE=1.6, and CPAM with DS=0.3 did not display reflection colors over the full cholesteric range, suggesting that the helicoidal twisting power of the cholesteryl group highly depends on the length of the spacer joining the cholesteryl group to the main chain and DS. The thermal stability and degree of order in the mesophase observed for the amylose derivatives highly depended on DE or DS. The results were discussed in terms of the difference ul the hydrogen bond, the internal plasticization, and the decoupling of the motion of side group with the main chain.

• Polymer(Korea)
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• v.34 no.2
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• pp.116-125
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• 2010

The thermotropic liquid crystalline behavior of the homologous series of combined-type liquid crystalline polymers, tri-O-{4-(4'-cyanophenylazo)phenoxy}alkyl celluloses (CACETn, where n, the number of methylene units in the spacer, is 2~10) have been investigated. The CACETn with n of 5 and 7 exhibited enantiotropic nematic phases, while other polymers showed monotropic nematic phases. The isotropic-nematic transition temperature($T_{iN}$) increased when n is increased up to 4, but it decreased with increasing n more than 5. The entropy change at $T_{iN}$ also reaches a minimum at n=5, before it increases again for n=6. The sharp change at n=5 may be attributed to the difference in arrangement in the side groups. The nematic-crystalline transition temperatures, in contrast with $T_{iNS}$, exhibited a distinct odd-even effect, suggesting that the average shape of the side chains in the crystalline phase is different from that in the nematic phase. The mesophase properties of CACETn were significantly different from those reported for tri-O-alkyl celluloses and poly[1-{4-(4'-cyanophenylazo)phenoxyalkyloxy}ethylene]s. The results were discussed in terms of the difference in the chemical structures of the main and side chains and the number of the mesogenic units per repeating unit.

• Applied Chemistry for Engineering
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• v.26 no.6
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• pp.698-705
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• 2015

Two series of symmetric dimesogenic compounds containing a butylene or 1-methylbutylene spacer as a flexible group were synthesized. The mesogenic groups of synthesized compounds consist of an azobenzene group with a terminal substituent. Chemical structures as well as, thermal, mesomorphic, and photochemical properties of the synthesized compounds were investigated using FT-IR, $^1H-NMR$, differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and UV-visible spectrometry. P-H, P-F, and $P-OC_6H_{13}$ showed monotropic liquid crystal phases, whereas the others showed enantiotropic liquid crystal phases. Compounds with butylene group as a flexible spacer exhibited wider mesophase temperature ranges and higher thermal transition temperatures than compounds containing a 1-methylbutylene group. Compounds with a high absolute value of the Hammett substituent constant exhibited high thermal transition temperatures and improved stability in the liquid crystal phase. Furthermore, in the absence or presence of UV light illumination, terminal substituents of the azomesogenic group were important factors in deciding the maximum absorbance wavelength (${\lambda}_{max}$) and the rate of photoisomerization (K).

• Journal of the Korean Electrochemical Society
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• v.4 no.3
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• pp.104-108
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• 2001

Naphthalene derived mesophase pitch WP) was spun into short fibers by using melt-blown technology. The pitch fibers oxidative stabilization were carried out heating rates of $2^{\circ}C/min,\;5^{\circ}C/min\;and\; 10^{\circ}/min$. The heating rate was a key factor to maximate the capacity of the Li-ion secondary battery through controlling the morphology of the graphitized fiber. The diameters of the melt-blown fibers prepared were in the range of $4{\mu}m\~16{\mu}m$ with functions of air jet speed, air temperature and the temperature of the nozzle. The graphitized fibers of $10{\mu}m$ diameters showed various morphological structure with heating rate of the stabilization. Radial, radial-random and skin-core cross-sectional structure of the fibers were observed at the respective heating rate of $2^{\circ}C/min\;5^{\circ}C/min\;and\;10^{\circ}C/min$. Most crystalline structure of graphite was obtained from the fiber stabilized at heating rate of $10^{\circ}C/min$ exhibiting the best anode performance with 400 mAh/g of capacitance and $96.8\%$ of charge/discharge efficiency.

• Applied Chemistry for Engineering
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• v.19 no.5
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• pp.504-511
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• 2008

Two kinds of nitroazobenzene derivatives: 4-{4'-(nitrophenylazo)phenoxy}alkanoic acids (NAAn, n = 2~8, 10, number of methylene units in the alkyl chain) and 4-{4'-(nitrophenylazo)phenoxy}alkanoyl chlorides (NACn, n = 2~8, 10) were synthesized, and their thermotropic liquid crystalline behaviors were investigated. NAA6 formed an enantiotropic nematic phase, while the remainders, except NAA2, showed monotropic nematic phases. Isotropic-nematic transition temperature ($T_{iN}$) and change of entropy (${\Delta}S$) at $T_{iN}$ for both of NAAn and NACn varied by the change of n, and pronounced odd-even effects of n were also observed. However, the $T_{iN}$ and ${\Delta}S$ values of NAAn were much higher than those of NACn. This fact may be attributed to the hydrogen bonding between carboxyl groups. Thermal properties and degree of order in the mesophase and the magnitude of the odd-even effects of both NAAn and NACn were significantly different from those reported for 4-(alkoxy)-4'-nitroazobenzenes. It was discussed in terms of the differences in the molecular anisotropy and the temperature-dependent flexibility of the substituted groups.