Low temperature phase transition in some thermotropic polyesters quenched from the liquid crystalline state

Frosini, Vittorio; Marchetti, A.; Petris, S. De

doi:10.1002/marc.1982.030031109

Cited by 29 publications

(5 citation statements)

References 2 publications

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“…After cooling the polyesters from the liquid isotropic melt or from the liquid crystalline state, glasslike modifications may be obtained. Evidence of mesomorphic structures in the glassy state has been found6, 16 and changes in heat capacity with the appearance of a glass transition have been shown in several copolyesters.17~'s Modes of motion in the main chain 17-'' or in the spacers 19,20 have been related with these findings. We have analyzed the existence and the nature of the relaxations in PTE-TOB by using DMTA and TSDC, at low and intermediate temperatures, in which differential calorimetry presents some shortcomings.…”

Section: X-ray Diffractograms For An Original Samplementioning

confidence: 94%

Relaxations in liquid crystalline poly(tetraethylene oxide terephthaloyl‐bis‐4‐oxybenzoate)

Gómez

Marco

Fatou

et al. 1995

J Polym Sci B Polym Phys

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The relaxation behavior of poly(tetra ethylene oxide terephthaloyl‐bis‐4‐oxybenzoate), PTETOB, was analyzed by thermally stimulated depolarization currents, TSDC, and dynamic mechanical techniques, DMTA, and the results compared with those obtained by differential scanning calcrimetry, thermo‐optical analysis, and x‐ray diffraction. In the low temperature region, −173–30°C, three main transitions were observed and assigned to the γ relaxation, the glass transition of the mesophase and the glass transition temperature of the amorphous material. The complex behavior observed in the range 110–160°C was as signed to a crystal‐crystal transition which competed with the formation of a mesophase and afterward the formation of a smectic A mesophase. At higher temperatures, was observed the transition from the smectic A mesophase to a nematic one, prior to the isotropization temperature. In the TSDC experiments the formation of a permanent electret was detected and the charges trapped in the mesophase were canceled only at the isotropization temperature. © 1995 John Wiley & Sons, Inc.

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Section: X-ray Diffractograms For An Original Samplementioning

confidence: 94%

Relaxations in liquid crystalline poly(tetraethylene oxide terephthaloyl‐bis‐4‐oxybenzoate)

Gómez

Marco

Fatou

et al. 1995

J Polym Sci B Polym Phys

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“…18 It should be noted that in main mesogen-nonmesogen liquid crystal polymers smectic phases were observed only in a very few cases. A recent review including this topic was given by Noel,20 where he summarized the works from Ober and Lenz, 21 Roviello and Sirigu, 22 Frosini and Marchetti, 23 of the ordered structure in this series of PEIMs. In particular, we try to understand what kind of ordered structure exists and what the effect of the even-odd alternation does in the monotropic liquid crystal state.…”

Section: Introductionmentioning

confidence: 99%

Ordered structures in a series of liquid-crystalline poly(ester imides)

Pardey¹,

Shen²,

Gabori³

et al. 1993

Macromolecules

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A series of poly(ester imide)s (PEIMs) has been synthesized from N-[4-(chloroformyl)phenyl] -4-(chloroformyl)phthalimide and different diols with methylene units of 4 to 12 (n). PEIMs with both even and odd methylene units exhibit a monotropic mesophase behavior during cooling due to the supercooling necessary for crystallization. Identification of this mesophase as a monotropic liquid crystal with smectic A order has been carried out via differential scanning calorimetry, wide angle X-ray diffraction (WAXD), small angle X-ray scattering, polarized light microscopy, and transmission electron microscopy. It is found that the methylene units in these chain molecules are also largely responsible for the formation of this liquid crystal phase. After investigating different types of main chain mesogen-nonmesogen liquid crystal polymers, a general concept considering the contributions to enthalpy aind entropy changes during the liquid crystal transitions may be associated with the relative rigidity, linearity, and regularity of the mesogenic groups compared to the methylene units. Detailed WAXD study of fiber and powder patterns indicates that the degree of orientation and the order correlation lengths along and perpendicular to the direction of chain molecules (chain lateral packing and layer structure) not only increase with the number of methylene units but also show an even-odd alternation. A possible chain packing model is suggested. The morphology and defects of this smectic A liquid crystal phtwe are also discussed.

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“…It has been pointed out that different solid modifications can be obtained for low molecular weight liquid crystals depending on the cooling rate and the temperature to which the sample is cooled from the anisotropic melt. 4 The existence of several crystalline polymorphs has also been reported for some liquid crystalline polymers.5 6 Thermotropic polyesters are one of the most commonly studied families of main-chain liquid crystalline polymers, and terephthaloylbis(oxybenzoic acid) is one of the principal mesogens used. Recently, the synthesis and characterization of this type of polymer, with linear methylene spacers ranging from 3 to 12 units, has been the subject of a number of publications.7-11 The thermal transitions and the effect of the flexible spacer length on the type of mesophase formed have been investigated.…”

Section: Introductionmentioning

confidence: 99%

Polymorphism in liquid crystalline poly[tetramethylene terephthaloyl bis(4-oxybenzoate)]

Pino¹,

Gómez²,

Cavazzini³

et al. 1992

Macromolecules

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Low temperature phase transition in some thermotropic polyesters quenched from the liquid crystalline state

Cited by 29 publications

References 2 publications

Relaxations in liquid crystalline poly(tetraethylene oxide terephthaloyl‐bis‐4‐oxybenzoate)

Relaxations in liquid crystalline poly(tetraethylene oxide terephthaloyl‐bis‐4‐oxybenzoate)

Ordered structures in a series of liquid-crystalline poly(ester imides)

Polymorphism in liquid crystalline poly[tetramethylene terephthaloyl bis(4-oxybenzoate)]

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