Liquid crystals. II. Unsymmetrical p-phenylene di-p-n-alkoxybenzoates

Haut, Stephen A.; Schroeder, D. C.; Schroeder, J. P.

doi:10.1021/jo00974a029

Cited by 35 publications

(7 citation statements)

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“…This result has also been seen in unsymmetrical p-phenylene di-p-n-alkoxybenzoates where T m decreased without a substantial decrease in T;. 20 The polymers of Series II, whose mesogenic groups consisted of only two consecutive aromatic ester units had, as expected, much lower melting points and clearing temperatures than those of Series I for corresponding lengths of polymethylene spacers; see Table II. The temperature ranges, !…”

Section: Thermotropic Liquid Crystal Meltssupporting

confidence: 67%

Liquid Crystal Polymers. V. Thermotropic Polyesters with Either Dyad or Triad Aromatic Ester Mesogenic Units and Flexible Polymethylene Spacers in the Main Chain

Ober¹,

Jin²,

Lenz³

1982

Polym J

145

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ABSTRACT:The thermal properties of two new series of thermotropic, liquid crystalline polyesters were studied by differential scanning calorimetry and on a hot-stage of a polarizing microscope. The first series contained an aromatic ester triad with a central terephthaloyl and two terminal oxybenzoyl units connected by a flexible polymethylene spacer containing from two to ten methylene units. The second series contained a head-to-head tail-to-tail aromatic ester dyad with one terephthaloyl and one oxybenzoyl unit and either a dimethylene or hexamethylene spacer. The melting temperatures and the transition temperatures for conversion from the mesophase to the isotropic phase (the clearing temperature) of the polyesters in the first series initially decreased in a zig-zag manner for polymers with up to nine methylene units but increased for the decamethylene polymer. The temperature ranges over which the mesophase formation occurred were generally broader for polymers containing an odd number of methylene units than for those with an even number of units. Most, if not all, of the polymers in both series formed nematic states on melting. The enthalpy and entropy changes for the clearing transition both increased with the length of the polymethylene spacer. Polymers of the second series possessed lower transition temperatures and narrower temperature ranges for mesophase formation, as would be expected for the shorter mesogenic unit.KEY The thermotropic, liquid crystalline behaviour of polymers having rigid mesogenic units interconnected through flexible spacers along the main chain has been predicted theoretically and is well known experimentally from reports over the past several years. 1 -5 We previously reported the synthesis and properties of several new series of polyesters having thermotropic liquid crystalline properties. 6 -8 In this work, two new series of polymers have been prepared with the structures shown below.linearly-aligned aromaic rings, the bis(pcarboxyphenyl) terephthalate moiety, and a polymethylene flexible spacer of varying length, n, as follows:The first series of polymers, Series I, was a group of linear polyesters having and alternating sequence containing a mesogenic triad unit with three * On sabbatical leave from the Chemistry

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Section: Thermotropic Liquid Crystal Meltssupporting

confidence: 67%

Liquid Crystal Polymers. V. Thermotropic Polyesters with Either Dyad or Triad Aromatic Ester Mesogenic Units and Flexible Polymethylene Spacers in the Main Chain

Ober¹,

Jin²,

Lenz³

1982

Polym J

145

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“…The ester, 4-[(4-butoxybenzoyl)oxy]phenol (8), was synthesized by the Schotten-Baumann reaction of a large excess of hydroquinone ( 6) with 4-butoxybenzoyl chloride (7) according to the literature method. 20 The cyanate ester (9) of the phenol (8) was then prepared by reaction with cyanogen bromide in the presence of triethylamine. The compound 4-[(4-butoxybenzoyl)oxy]phenyl cyanate (9) was then cyclotrimerized in near quantitative yield in carbon tetrachloride using phosphorus pentachloride as catalyst to form the triazine model compound 2,4,6-tris [4-[ (4-butoxybenzoyl)oxy]phenoxy]-l,3,5-triazine (10).…”

Section: Resultsmentioning

confidence: 99%

Rigid-rod thermosets based on 1,3,5-triazine-linked aromatic ester segments

Barclay¹,

Ober²,

Papathomas³

et al. 1992

Macromolecules

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Liquid-crystalline (LC) thermosets were prepared by the thermal cyclotrimerization of dicyanate compounds of ring-substituted bis(4-hydroxyphenyl) terephthalates. The resulting triazine networks formed a mesophase as the curing reaction proceeded, thereby enabling alignment in applied fields. Alignment of the LC phase during the curing process under the influence of a magnetic field produced oriented triazine networks with a smecticlike molecular organization. The effect of this anisotropy on the properties of these networks was investigated by both wide-angle X-ray diffraction and by measuring the coefficient of thermal expansion parallel and perpendicular to the direction of alignment. Remarkably well-oriented triazine networks were obtained (f ~0.50) with low values of the coefficient of thermal expansion observed (17 ppm/°C) in the direction of the applied field. The triazine networks have glass transition temperatures of ~190 °C and show little decomposition until ~440 °C. The alignment of the LC triazine networks induced by curing in magnetic fields was found to be thermally stable until at least 100 °C above the glass transition temperature.

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“…An attempt was made to estimate the "virtual" Sm-N transition temperatures of the others by extrapolation of data from their binary mixtures.' [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] The transition points of mixtures of the ester under investigation with a suitable second ' The smectic mesophases of the methyl and ethyl homologs exhibit focal-conic fan textures (smectic A); those of the other homologs are grainy and/or labyrinthine (smectic C).…”

Section: Resultsmentioning

confidence: 99%

Liquid crystals. II. Unsymmetrical p-phenylene di-p-n-alkoxybenzoates

Cited by 35 publications

References 0 publications

Liquid Crystal Polymers. V. Thermotropic Polyesters with Either Dyad or Triad Aromatic Ester Mesogenic Units and Flexible Polymethylene Spacers in the Main Chain

Liquid Crystal Polymers. V. Thermotropic Polyesters with Either Dyad or Triad Aromatic Ester Mesogenic Units and Flexible Polymethylene Spacers in the Main Chain

Rigid-rod thermosets based on 1,3,5-triazine-linked aromatic ester segments

Liquid Crystals: VII. Smectic-Nematic Transition Temperature as a Function of Alkyl End Group Length inp-Phenylene Di-p-n-alkoxybenzoates

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