Transitions and Relaxations in Mesophase Polymers: Thermotropic Liquid Crystalline Polyesters with Mesogenic Groups in the Main Chain

Frosini, Vittorio; Petris, S. De; Chiellini, Emo; Galli, Giancarlo; Lenz, Robert W.

doi:10.1080/00268948308073477

Cited by 45 publications

(19 citation statements)

References 9 publications

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“…The open ones are f max estimated with the shift factor determined by the empirical method. f max at the smectic LC temperatures cannot be determined directly by the DMA spectra; however, it can be estimated by using a T calculated from Equation (1). f max at various temperatures are shown numerically in Table 2.…”

Section: Mechanical Measurementsmentioning

confidence: 99%

“…However, the LCP solid exhibits relaxation processes similar to those of conventional glassy polymers. [1][2][3][4][5][6][7][8][9] The Summary: Anisotropy in molecular motions of a glassy smectic CA (SmCA) liquid crystal of a main-chain BB-5(3-Me) polyester was examined by dynamic mechanical analysis (DMA) for fibrous monodomain samples with two distinct orientations of smectic layers perpendicular and parallel to the fiber axis. The a-process attributed to micro-Brownian motion of the polymer on the glass transition shows clear anisotropy explainable by the nature of the smectic layer structure.…”

Section: Introductionmentioning

confidence: 99%

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Thermotropic Liquid Crystals of Main‐Chain Polyesters having a Mesogenic 4,4′‐Biphenyldicarboxylate Unit, 14

Osada

Koike

Tagawa

et al. 2004

Macro Chemistry & Physics

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Summary: Anisotropy in molecular motions of a glassy smectic CA (SmCA) liquid crystal of a main‐chain BB‐5(3‐Me) polyester was examined by dynamic mechanical analysis (DMA) for fibrous monodomain samples with two distinct orientations of smectic layers perpendicular and parallel to the fiber axis. The α‐process attributed to micro‐Brownian motion of the polymer on the glass transition shows clear anisotropy explainable by the nature of the smectic layer structure. Time‐temperature superposition is applicable to the α‐process, so that the frequency of the micro‐Brownian motion in the SmCA phase can be estimated despite the narrow frequency range in DMA. The results suggest that the decoupling of the molecular motions in two characteristic directions are parallel and perpendicular to the layer. The amplitude of the micro‐Brownian motion in the layer normal direction is 3 times smaller than that in the layer direction, and the frequency in the layer normal direction is 2.5 times higher than that in the layer direction.Illustration of molecular packing structures: fiber A (left side) and fiber B (right side) with the orientations of polymers parallel and perpendicular to the fiber, respectively.imageIllustration of molecular packing structures: fiber A (left side) and fiber B (right side) with the orientations of polymers parallel and perpendicular to the fiber, respectively.

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Section: Mechanical Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Thermotropic Liquid Crystals of Main‐Chain Polyesters having a Mesogenic 4,4′‐Biphenyldicarboxylate Unit, 14

Osada

Koike

Tagawa

et al. 2004

Macro Chemistry & Physics

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“…The resulting solid is hence regarded as liquid crystal glass. 18,23,24,[65][66][67][68][69][70][71][72][73][74][75][76][77][78] While conventional glass, namely isotropic liquid glass, is characterized by an absence of long-range order, the nematic LC glass possesses a simple orientational order of rod-like molecules and the smectic LC glass has the long-range one-dimensional positional order as well. These LC glasses are thus expected to provide new insight into dynamics of glassy materials representing a topic of current interest in condensed matter physics.…”

Section: Hairpin Folding In Nematic Liquid Crystalline Fieldmentioning

confidence: 99%

“…The -process can be connected with the motion of the aromatic part including the ester group. 67,79,80 The -process is attributed to local rotation of methylene group commonly observed for polymers containing methylene sequences. 79 These mechanical relaxations are similar to those observed in the isotropic liquid glass of the conventional polymers.…”

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confidence: 99%

Several Interesting Fields Exploited through Understanding of Polymeric Effects on Liquid Crystals of Main-Chain Polyesters

Tokita

Watanabe

2006

Polym J

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ABSTRACT:We review our experimental results on the structural characteristics of polymeric liquid crystals collected through our studies on the main-chain liquid crystalline polyesters with mesogenic biphenyl groups connected by flexible alkyl spacer. The polyesters studied, designated as BB-n where n is the number of carbon atoms in the alkyl spacer unit, form smectic mesophases. Of interest is that the type of smectic phase alters depending on the odd-even parity of n. An ordinal smectic A phase is formed by BB-n with even n, whereas BB-n with odd n forms a new type of smectic phase, so called smectic CA phase, in which the long axis of the mesogen is tilted against the layer normal and the tilting direction is opposite between neighboring layers. Finding of smectic CA phase with specific packing symmetry leads to a distinct discovery of ferroelectric and antiferroelectric phases in achiral molecular systems. In these smectic phases, the polymer chain assumes more extended conformation. Such an extended conformation, however, does not continue over the whole length of the polymer and hairpin folding arises to gain entropy. In the smectic phases, the hairpin foldings are located at a limited space, forming chain folded lamellae. Unusual shear flow orientation and anomalous crystallization behavior are explained based on the chain folded lamellar structure. Solid state morphology of liquid crystalline polymer is also presented. Since the degree of liquid crystallinity is almost 100%, the solid phase cooled through the formation of liquid crystals is composed of crystal and liquid crystal glass. Liquid crystal glass is studied and properties are discussed in a comparison with those of conventional isotropic glass.

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“…The glass transition temperature had been previously found to be located at 47°C by dynamic-mechanical measurements on HTH/ TEG samples quenched from the isotropic state. 8 On cooling ( Figure 1B) the minimum of the isotropic-mesophase exotherm is located at 211 °C, this process showing a very limited degree of supercooling (6°C). A weak and shallow signal is centered at l 80°C due to a mesophase-mesophase transition, while crystallization occurs at 90°C.…”

Section: Thermal Analysismentioning

confidence: 99%

Semiflexible Thermotropic Liquid-Crystalline Polymers: The Characterization of a Polyester-Polyether

Galli

Chiellini

Torquati

et al. 1989

Polym J

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ABSTRACT:The liquid crystal behavior of the thermotropic polyester derived from (4,4'-terephthaloyldioxy)dibenzoic acid and tetraethylene glycol was studied by differential scanning calorimetry, polarizing microscopy, and X-ray diffraction. The polymer sample exhibits the phase sequence isotropic-nematic-smectic A-smectic E-crystal, with decreasing temperature. Attention was devoted to the optical textures of the mesophases, as compared to those of low molar mass mesogens, and unusual high strength singularities were detected in the schlieren texture of the nematic phase. KEY WORDSLiquid-Crystalline Polymers/ Thermotropic Polyesters/ Liquid-Crystalline Polymorphism/ Smectic Mesophases / Schlieren Textures/ glycol ethers of different lengths:The thermotropic liquid-crystalline behavior of main chain polymers comprising alternating mesogenic units and flexible spacers is well established and attracts ever increasing interest. The great majority of such polymers presents only one mesophase, typically nematic ( or cholesteric ), but smectic phases have also been observed, including ordered smectic B 1 , E 2 , G 3 or H 4 phases. A few examples are known of mesophase polymorphism5, this feature being in marked contrast with what is most commonly observed in low molecular weight mesogens.In a previous paper 6 some of us reported on the synthesis and characterization of the thermotropic properties of a class of polyesters derived from 4,4' -(terephthaloyldioxy)dibenzoic acid (HTH) and ethylene (or propylene) Polymer samples having n = 2, 3, or 4 displayed two different enantiotropic liquidcrystalline phases, the lower temperature mesophase being a provisionally unidentified smectic phase and the higher temperature mesophase being recognized as nematic. 6 In the same context, unusual textural behaviors were observed in such polymers, especially at the mesophase-mesophase transition. All these features have stimulated further investigation and accordingly the polyester sample of that class with n = 4, here designated as HTH/TEG, was freshly prepared from HTH diacid chloride and tetraethylene glycol (TEG) and t To whom correspondence should be addressed.

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Transitions and Relaxations in Mesophase Polymers: Thermotropic Liquid Crystalline Polyesters with Mesogenic Groups in the Main Chain

Cited by 45 publications

References 9 publications

Thermotropic Liquid Crystals of Main‐Chain Polyesters having a Mesogenic 4,4′‐Biphenyldicarboxylate Unit, 14

Thermotropic Liquid Crystals of Main‐Chain Polyesters having a Mesogenic 4,4′‐Biphenyldicarboxylate Unit, 14

Several Interesting Fields Exploited through Understanding of Polymeric Effects on Liquid Crystals of Main-Chain Polyesters

Semiflexible Thermotropic Liquid-Crystalline Polymers: The Characterization of a Polyester-Polyether

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