• Polymer(Korea)
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• v.35 no.2
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• pp.176-182
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• 2011

Liquid crystalline aromatic polyesters (LCPs) are representative examples of thermotropic liquid crystalline polymers, whose structure-property relationships have been the subject of many researches. In this study, we synthesized organo-soluble liquid crystalline aromatic polyesters, and their composites with acetylene-terminated thermoset resins were prepared and characterized. Soluble LCPs were synthesized by employing 6-hydroxy-2-naphthoic acid, terephthalic acid, isophthalic acid, and 4-aminophenol as monomers via condensation polymerization based on transesterfication and transamidation. Acetylene-terminated thermoset resins were synthesized by the reaction of 4-ethynylaniline with terephthaloyl dichloride, isophthaloyl dichloride or 4,4'-biphenyldicarbonyl dichloride. We prepared the soluble LCP/thermoset composites by solution blending followed by thermal treatment. The thermal stability, thermal expansion coefficient, and dielectric properties of the composite were studied.

• Elastomers and Composites
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• v.44 no.3
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• pp.329-335
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• 2009

Four series of novel liquid crystalline polyurethanes were synthesized by the polyaddition reaction of diisocyanates such as 2,6-tolylene diisocyanate (2,6-TDI), 2,5-tolylene diisocyanate (2,5-TDI), 2,4-tolylene diisocyanate (2,4-TDI), and 1,4-phenylene diisocyanate (1,4-PDI) with 4,4'-bis(5-hydroxypentoxy)biphenyl (BP5). 4,4'-bis(5-hydroxypentoxy)biphenyl exhibited a smectic type mesophase. Mesophase was found for all synthesized liquid crystalline polyurethanes except 1,4-PDI/BP5. The structures and the thermal properties of polyurethanes were studied by using FT-IR and ^1H$ NMR spectroscopy, DSC measurements and a polarizing microscope equipped with a heating stage.

• 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.20 no.6
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• pp.603-611
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• 2009

Thermotropic liquid crystalline behavior of a homologous series of penta-O-4-{4'-(cyanophenylazo)phenoxy}alkyl-D-glucopyranoses(CAGETn, n = 2~10, the number of methylene units in the spacer) has been investigated. The CAGETn with n of 2 and 7 exhibited enantiotropic nematic phases whereas other derivatives showed monotropic nematic phases. This is the first report of glucose derivatives that form thermotropic nematic phases. The isotropic-nematic transition temperatures ($T_{iNS}$) of CAGETns and their entropy variation at $T_{iN}$ showed the odd-even effect as a function of n. This behavior was rationalized in terms of the change in the average shape of the side chains as the parity of the spacer is varied. This rationalization also accounts for the observed variation of nematic-crystalline phase transition temperatures ($T_{NkS}$) and associoated entropy change at $T_{Nk}$. The entropy change at $T_{iN}$ or $T_{Nk}$ reaches a mininum at n = 3, before it increases again for n = 4. This may be attributed to the difference in the arrangement of the side groups. The mesophase properties of CAGETns were entirely different from those reported for partially or fully alkylated glucopyranoses. This result suggests that the degree of substitution and chemical structure of the substituents play an important role in the formation of the mesophase structures in the liquid crystals.

• Polymer(Korea)
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• v.36 no.1
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• pp.76-87
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• 2012

Three kinds of hydroxypropyl cellulose (HPC) derivatives, [6-{4-(4-cyanophenylazo)phenoxy}]hexyloxypropyl celluloses (CAHPCs) with degree of etherification (DET) ranging from 0.4 to 3, fully substituted acrylic acid esters of HPC (HPCA) and CAHPCs (CAHPCAs) were synthesized. The crosslinked HPCA (HPCAG) and CAHPCAs (CAHPCAGs) were also prepared by exposing thermotropic mesophases of HPCA and CAHPCAs to UV light. Both CAHPCs and CAHPCAs with DET ${\leq}$ 1.2, as well as HPC and HPCA, formed enantiotropic cholesteric phases whose optical pitches(${\lambda}_m$'s) increase with temperature, wheras both CAHPCs and CAHPCAs with DET ${\geq}$ 1.4 showed monotropic nematic phases. CAHPCAGs with DET ${\leq}$ 1.2, as well as CAHPCAs with DET ${\leq}$ 1.2, exhibited reflection colors in a wide temperature range. On the other hand, CAHPCAGs with DET ${\geq}$ 1.4, as well as CAHPCAs with DET ${\geq}$ 1.4, showed Schileren textures typical of nematic phase, indicating that the liquid crystalline structure is virtually locked upon photocrosslinking. The isotropization temperatures($T_i$'s) of both CAHPCAs and CAHPCAGs decreased with increasing DET. The $T_i$ of CAHPCAG, however, was higher than that of CAHPCA at the same DET. Moreover, the temperature dependence of ${\lambda}_m$ of CAHPCAGs was much weaker than that of CAHPCAs.

• Polymer(Korea)
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• v.32 no.5
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• pp.489-496
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• 2008

The thermotropic liquid crystalline behavior of a homologous series of poly[1-{4-(4' nitrophenylazo) phenoxycarbonylalkanoyloxy}ethylene]s (NAPEn, n = $2{\sim}8$,10, the number of methylene units in the spacer) have been investigated. All of the homologues formed monotropic nematic phases. The glass transition temperatures decreased with n. This is attributed to a plasticization of the backbone by the side chains. The isotropic-nematic phase transition temperatures decreased with increasing n up to 7 and showed the odd-even effect. However it became almost constant when n is more than 7. This behavior was rationalized in terms of the change in the average shape of the side chain on varing the parity of the spacer. This rationalization also accounts for the observed variation of the entropic gain for the clearing transition. The mesophase properties of NAPEn were entirely different from those reported for the polymers in which the azobenzene groups are attached to polyacrylate, polymathacrylate, and polystyrene backbones through polymethylene spacers. The results indicate that the mode of chemical linkage of the side group with the main chain plays an important role in the formation, stabilization, and type of mesophase.

• Applied Chemistry for Engineering
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• v.22 no.4
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• pp.358-366
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• 2011

A homologous series of linear liquid crystal dimers, the ${\alpha},{\omega}$-bis(4-cyano-azobenzene-4'-oxy)alkanes (CATWETn, where n, the number of methylene units in the spacer, is 2~10) were synthesized, and their thermotropic liquid crystalline phase behavior were investigated. The CATWETn with n of 3 and 6 exhibited monotropic nematic phases, whereas other derivatives showed enantiotropic nematic phases. The nematic-isotropic transition temperatures of the dimers and their entropy variation at the phase transition showed a large odd-even effect as a function of n. This phase transition behavior was rationalized in terms of the change in the average shape of the spacer on varying the parity of the spacer. The thermal stability and degree of order in the nematic phase and the magnitude of the odd-even effect of CATWETn were similar to those for the methoxy-, nitro-, and pentyl-substituted dimers, while they were significantly different from those for the monomesogenic compounds, 1-{4-(4'-cyanophenylazo)phenoxy}alkylbromides and the side-chain liquid-crystalline polymers, the poly[1-{4-(4'-cyanophenylazo)phenoxyalkyloxy}ethylene]s. The results were discussed in terms of 'virtual trimer model' by Imrie.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3653-3659
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• 2015

This paper describes the reactive compatibilization of blends of a wholly aromatic thermotropic copolyester liquid crystalline polymer (TLCP) with random copolymers of ethylene and acrylic acid (EAA) and their salts. Blends were prepared by melt mixing in an intensive batch mixer, and the formation of a graft copolymer due to acidolysis between the TLCP and the acrylic acid group of the ionomer was evaluated. Chemical reaction was assessed by torque measurement during melt mixing and by thermal analysis and morphological observation. The Na-salt of the EAA ionomers was especially effective at promoting a grafting reaction. The extent of reaction depended not only on the cation, but also composition of the ionomer and reaction time. The product of the grafting reaction between the TLCP and a sodium-neutralized ionomer proved to be an effective compatibilizer for TLCP and EAA ionomers.

• Polymer(Korea)
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• v.28 no.1
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• pp.92-102
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• 2004

(6-Cholesteryloxycarbonylpentoxypropyl)celluloses (CHPCs) with degree of esterification (DE) ranging from 2.25 to 2.91 were synthesized by reacting hydroxypropyl cellulose with 6-cholesteryloxycarbonylpentanoyl chloride. The acrylic esters of CHPCs (CHPCEs) and their photocrosslinked films with liquidcrystalline order were also synthesized. The thermotropic properties of mesophase for both uncrosslinked and crosslinked samples and the swelling behavior of the crosslinked samples in acetone were investigated. The hydroxypropyl cellulose exhibited an enantiotropic cholesteric phas, while all the uncrosslinked cholesterylbearing samples exhibited a monotropic cholesteric phases; the 6-cholesteryloxycarbonylpentanoyl chloride also showed a monotropic smectic phase. The hydroxypropyl cellulose formed a right-handed helix whose optical pitch (λ$\sub$m/) increases with temperature, whereas all the uncrosslinked derivatives farmed left-handed helices whose λ$\sub$m/'s decreased with temperature. The thermal stability of the mesophase and the magnitude of λ$\sub$m/ at the same temperature for both CHPCs and CHPCEs decreased with increasing DE. All the crosslinked samples, in constrast with CHPCEs, did not display reflection colors but exhibited an anisotropic swelling characteristic of crosslinked gel retaining liquid-crystalline order.

• Korean Chemical Engineering Research
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• v.48 no.5
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• pp.615-620
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• 2010

In this study, five series of novel polyurethanes was synthesized by the polyaddition reaction of diisocyanates such as 2,6-tolylene diisocyanate(2,6-TDI), 2,5-tolylene diisocyanate(2,5-TDI), 2,4-tolylene diisocyanate(2,4-TDI), and 1,4-phenylene diisocyanate(1,4-PDI), hexamethylene diisocyanate(HDI) with 4,4'-Bis(3-hydroxypropoxy)biphenyl (BP3), 4,4'-bis(3-hydroxypropoxy)biphenyl exhibited a smectic type mesophase. Monotropic mesophase was found for all synthesized liquid crystalline polyurethanes except HDI/BP3. In contrast, 1,4-PDI/BP3 without a methyl substituent in the phenylene unit exhibited no explicit mesomorphic behavior, which was confirmed by DSC and polarizing microscopy experiments. Structures of the compound were identified by FT-IR and $^1H$-NMR spectroscopies. Their phase transition temperatures and thermal stability were also investigated by differential scanning calorimetry(DSC), polarized optical microscopy(POM) and x-ray diffraction analysis.