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

Pino, Javier del; Gómez, M. A.; Cavazzini, Marco; Ellis, Gary; Fatou, J. G.

doi:10.1021/ma00044a027

Cited by 18 publications

(13 citation statements)

References 8 publications

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“…This polymer shows a crystal-nematic transition at 558 K, and a nematic-isotropic transition at 623 K as measured by DSC. 10 The glass transition is hardly observed by this technique due to the crystallinity, but T g was found to be equal to 336 K as measured by the position of the DMA peak assigned to this transition (see Fig. 2).…”

Section: Resultsmentioning

confidence: 80%

“…It presents two crystalline forms, depending on the thermal treatment of the sample. 10 Form I exists when the sample is precipitated from solution, and shows an irreversible solid-solid transformation upon heating prior to the crystal-nematic mesophase transition. Form II is obtained when the sample is slowly cooled or quenched from the mesophase.…”

Section: Resultsmentioning

confidence: 99%

“…10,[13][14][15] The intermediate products and the final polymers were characterized using elemental analysis, 1 H-NMR, 13 C-NMR, and vibrational spectroscopy, which assured the structure and the purity of the materials. The inherent viscosity of the four polymers was measured in p-chlorophenol at 45°C, and found to range between 0.29 -0.39 dL ⅐ g Ϫ1 .…”

Section: Methodsmentioning

confidence: 99%

“…The determination of the transitions and the identification of the different phases were carried out by DSC, X-ray diffraction, and optical microscopy, whose specific technical details can be found elsewhere. 10,[13][14][15] Dynamic-mechanical studies were performed on the four polymers on a TA Dynamic Mechanical Thermal Analyzer, working in the flexural bending mode. The experiments were carried out in a temperature range from 123 to 423 K at frequencies varying from 0.1 to 1 Hz using a heating rate of 5 K/min.…”

Section: Methodsmentioning

confidence: 99%

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Effect on TSDC relaxation spectra of substitutions in the mesogenic unit and in the flexible spacer of poly(tetramethylene terephtaloyl-bis-4-oxybenzoate)

Hernández

Laredo

Bello

et al. 1999

J. Polym. Sci. B Polym. Phys.

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Section: Resultsmentioning

confidence: 80%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Effect on TSDC relaxation spectra of substitutions in the mesogenic unit and in the flexible spacer of poly(tetramethylene terephtaloyl-bis-4-oxybenzoate)

Hernández

Laredo

Bello

et al. 1999

J. Polym. Sci. B Polym. Phys.

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“…Many theoretical and experimental works have examined the planarity of the benzene rings and adjacent carbonyl groups, and the site of bond rotation near the phase transition (solid-to-liquid crystal) temperature. [1][2][3] We recently characterized an LC oligomer with a biphenyl ester moiety using Raman spectroscopy to better understand the mechanism of the conformational change that accompanies modification of the intermolecular interactions. 4,5 In order to understand the mechanism of the conformational changes during the phase transition, we compared the spectral evolution of the combination mode of the aromatic C-C(=O)O and C(=O)O stretching vibrations at 1274 cm −1 with those of analogous molecules as a function of temperature, and found that bond rotation occurs around the aromatic C and the C(=O)O near the ethyl terminal.…”

mentioning

confidence: 99%

Determining the Dynamic Sequence of Carbonyl Groups in a Rod-Coil Liquid Crystalline Oligomer Using Two-Dimensional Raman Correlation Spectroscopy

Jung¹,

Yu²,

Yu³

2004

Journal of the Korean Chemical Society

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We investigated the order of local movement of functional groups (-C(=O)O) in a liquid crystalline (LC) oligomer (12-4) using 2D Raman correlation spectroscopy. The results suggest that the free carbonyl near the ethyl terminal group moved first, followed by the hydrogen-bonded group. The free carbonyl group between the biphenyl groups rarely moved. Interestingly, 2D sample-to-sample correlation spectroscopy (2D STSCS) revealed that some of the carbonyl modes started to move at far below (50 o C) the LC temperature (135 o C), countering conventional beliefs.

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Modifications in the mesogenic unit of poly(oxytetramethyleneoxycarbonyl‐3‐chloro‐1,4‐phenyleneoxyterephthaloyloxy‐2‐chloro‐1,4‐phenylenecarbonyl)

Pino

Gómez

Ellis

et al. 1994

Macro Chemistry & Physics

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The effect of asymmetrical chlorine substitution in the mesogenic unit of poly(oxytetramethyleneoxycarbonyl-3-chloro-l,4-phenyleneoxyterephthaloyloxy-2-chloro-l,4-phenylenecarbonyl) (1) has been studied by means of differential scanning calorimetry, optical microscopy and X-ray diffraction. The polymer presents three-dimensional ordering, in spite of the substitution, and shows a transition to a nematic mesophase at 274 "C and to the isotropic melt at 319 "C. As for the unsubstituted polymer poly(oxytetramethyleneoxycarbonyl-1,4-phenyleneoxyterephthaloyloxy-l,4-phenylenecarbonyl), two different crystalline forms have been observed and some information about their structure has been obtained by Fourier-Transform Raman spectroscopy and 13C solid-state nuclear magnetic resonance. First results indicate that the most important structural differences between both polymorphs occur in the mesogenic unit. lntroductionMain-chain liquid-crystalline polymers have been the subject of much interest during recent years One objective in their study is the possibility of reducing their high melting temperatures in order to improve their melt processability. In principle, this can be achieved by introducing flexible spacers between the mesogens, lateral substituents in the mesogenic unit, or by copolymerization. From a scientific point of view, it has also been a goal to correlate the nature, stability and kinetics of the mesophases formed with such structural variations 5-7). Thermotropic polyesters with a 4,4'-terephthaloyldioxydibenzoic acid mesogen moieties and flexible linear spacers are one of the most common families of main-chain liquid-crystalline polymers, and the synthesis and properties of these polymers with linear methylene spacers have been described by several authors 5* 8, g). Recently, the effect of symmetric or asymmetric lateral substitution in the flexible spacer has been studied ' I ) , and in all cases the temperatures for the crystal --t liquid crystal transition (T, ) and the mesophase --t isotropic transition (Ti) were lowered considerably with respect to the unsubstituted polymer, and the formation of three-dimensional order was hindered.On the other hand, the presence of pendant substituents in the mesogenic unit may also affect the properties of the mesophase formed. The steric hindrance caused by bulky substituents will increase the separation of the mesogenic units in adjacent polymer chains, and should lead to a reduction of the transition temperatures, and in some cases lead to the loss of the formation of a three-dimensional order. The effect of lateral substituents on the central ring in a variety of polyesters with three aromatic units in the mesogen has been reported in the literature 5 , ').

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

Cited by 18 publications

References 8 publications

Effect on TSDC relaxation spectra of substitutions in the mesogenic unit and in the flexible spacer of poly(tetramethylene terephtaloyl-bis-4-oxybenzoate)

Effect on TSDC relaxation spectra of substitutions in the mesogenic unit and in the flexible spacer of poly(tetramethylene terephtaloyl-bis-4-oxybenzoate)

Determining the Dynamic Sequence of Carbonyl Groups in a Rod-Coil Liquid Crystalline Oligomer Using Two-Dimensional Raman Correlation Spectroscopy

Modifications in the mesogenic unit of poly(oxytetramethyleneoxycarbonyl‐3‐chloro‐1,4‐phenyleneoxyterephthaloyloxy‐2‐chloro‐1,4‐phenylenecarbonyl)

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