Structure and molecular mobility in liquid crystalline copolyesters

Zachmann, H. G.; Spies, C.; Thiel, Steffen

doi:10.1088/0031-8949/1993/t49a/042

Cited by 5 publications

(8 citation statements)

References 15 publications

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“…It is worth mentioning that the Δε β values derived for the PET- co -PHB 70:30 copolyester are higher than the reported ones by Gedde et al for PET- co -PHB 20:80 (Δε β ≈ 0.8) . It is noted that in PET- co -PHB copolymers a high degree crystallinity can develop, provided the molar fraction of PHB is higher than 80% . On the other hand, it has been shown that Δε β decreases as crystallinity increases, owing to the immobilization of the dipoles within the crystalline phase .…”

Section: Discussionmentioning

confidence: 63%

“…A recovery of the liquid crystalline order is achieved once again, provided the sample is heated above 100 °C. The glass transition temperature of the amorphous state, ( T g ) I = 95 °C, is higher than the corresponding one of the liquid crystalline state, ( T g ) LC = 60 °C. , …”

Section: Resultsmentioning

confidence: 80%

“…PET- co -PEN- co -PHB Ternary Copolyester. The ternary copolyester PET- co -PEN- co -PHB (35:35:30) is a material in which both the liquid crystalline and the amorphous states can be frozen-in by appropriated thermal treatments. , At thermal equilibrium, the terpolymer is liquid crystalline up to T > 160 °C. A progressive isotropization of the system is observed at higher temperatures, which is completed to 290 °C.…”

Section: Resultsmentioning

confidence: 99%

“…Much research activity continues to be directed to the understanding of the structure and chain dynamics in copolymers formed by poly(ethylene terephthalate) (PET), poly(ethylene 2,6-naphthalenedicarboxylate) (PEN), and poly( p -hydroxybenzoic acid) (PHB). − X-ray diffraction and neutron scattering studies have analyzed the crystallization behavior and the transitions into the liquid crystalline states and on the melting of these copolyesters. ,− These investigations reveal the following: (1) the copolyesters form liquid crystalline states only if the content of PHB is larger than 30−40%; (2) the copolyesters crystallize, on cooling from the mesophase, when the PEN or PET content exceeds 50%; (3) for PET- co -PEN copolymers no liquid crystalline states are formed; and (4) a simultaneous crystallization of both components never occurs . The mechanical properties of these materials have been investigated using the microhardness technique, and a relationship between this property and changes in the microstructure has been observed. , …”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Influence of Liquid Crystalline Order on the Dielectric Relaxation of Random Copolyesters of PET, PEN, and PHB

et al. 1996

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The dielectric constant and dielectric loss values for random copolyesters of poly(ethylene terephthalate) (PET), poly(ethylene 2,6-naphthalenedicarboxylate) (PEN), and poly(p-hydroxybenzoic acid) (PHB) have been determined in the 103−106 Hz frequency range. The variation of the dielectric properties with temperature has been related mainly to two processes: (1) The α relaxation, which is associated to the glass transition and which has been shown to be dependent on the molecular order of the systems. Copolymers with liquid crystalline order exhibit an α relaxation process occurring at lower temperatures than the amorphous ones. (2) The β process which has been assigned to a local motion of the ester groups attached to both sides of the aromatic rings. The β process also depends on the molecular order. The existence of a liquid crystalline state increases the dipolar correlation of both the β and the α relaxation processes.

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Section: Discussionmentioning

confidence: 63%

Section: Resultsmentioning

confidence: 80%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Influence of Liquid Crystalline Order on the Dielectric Relaxation of Random Copolyesters of PET, PEN, and PHB

et al. 1996

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A comparative dielectric study on the molecular dynamics of the liquid crystalline and the amorphous state of copolyesters

Ahumada

Ezquerra

Nogales

et al. 1995

Macromol. Rapid Commun.

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The complex dielectric permittivity has been measured in the lo3 -lo6 Hz frequency range for selected random copolyesters of poly(ethy1ene terephthalate). The variation of the dielectric properties with temperature has been qualitatively related mainly to two processes. The a relaxation, which is associated with the glass transition, has been shown to be dependent on the molecular order of the systems. TheP relaxation process has been assigned to local motions of the ester groups attached to both sides of the aromatic rings. The P process is also shown to exhibit a dependence on molecular order.

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Thermally stimulated depolarization currents in poly (ethyleneterephthalate‐ran‐p‐hydroxybenzoates)

D’Souza

2001

Polymer Engineering & Sci

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Thermally stimulated polarization (TSPC) and depolarization currents (TSDC) are measured on polyethylene terephthalate (PET) copolymerized with p‐hydroxy benzoic acid (PHB). These systems are important since they comprise components of many commercial polymer liquid crystals (PLCs). There has been some speculation about the origins of the multiple transition peaks in TSDC of PLCs and secondary peaks have frequently been designated as resulting from Maxwell‐Wagner interphase polarization. The applicability of this designation for main chain PLCs has been investigated. TSDC as a function of field strength and window polarization has been conducted and the transitions have been identified as glass transition peaks as opposed to space charge relaxations. A comparison of the TSDC current versus the polarization current (TSPC) reveals that TSPC is not generated for transitions associated with the PHB component.

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Structure and molecular mobility in liquid crystalline copolyesters

Cited by 5 publications

References 15 publications

Influence of Liquid Crystalline Order on the Dielectric Relaxation of Random Copolyesters of PET, PEN, and PHB

Influence of Liquid Crystalline Order on the Dielectric Relaxation of Random Copolyesters of PET, PEN, and PHB

A comparative dielectric study on the molecular dynamics of the liquid crystalline and the amorphous state of copolyesters

Thermally stimulated depolarization currents in poly (ethyleneterephthalate‐ran‐p‐hydroxybenzoates)

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