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Abstract  

The non-isothermal crystallization behavior of poly(trimethylene terephthalate) (PTT) and its blends with a liquid crystalline polymer, namely Vectra A950 (VA), was studied by differential scanning calorimetry. The values of the half-time of crystallization, t 0.5 and the parameter F(T) in the combined Avrami and Ozawa equation indicated that VA can enhance the PTT crystallization rate by acting as a nucleating agent. The crystallization activation energy of the PTT phase increased with increasing VA content. The blends were immiscible, as can be inferred from their morphology. Thermogravimetric analysis of the blends revealed improved thermal stability by the incorporation of VA.

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combination of properties. Over the past several decades, blending of liquid crystalline polymer (LCP) with commodity polymers resulting in the so-called in situ microfibrillar-reinforced composite [ 1 , 2 ] has been known to exhibit excellent mechanical

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Introduction Since the last two decades, thermotropic liquid crystalline polymers (TLCPs) have gained much research attention in both academic and industrial fields, due to its various advantages such as superior strength

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Liquid crystalline polymers

III. Characterization by thermo-optometry of some copolyethers containing an oxetane ring in the main chain

Journal of Thermal Analysis and Calorimetry
Authors: N. Hurduc, A. Stoleru, D. Pavel, and C. I. Simionescu

The suitabilities of thermo-optometry and differential scanning calorimetry for the characterization of certain copolyethers were compared. Under certain conditions, such polymers do not exhibit the endotherm signal corresponding to the solid/liquid crystalline transition in the DSC curves. Thermo-optometry provides evidence of these phase transitions into the liquid crystalline state, and is a very useful additional method.

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The thermotropic copolyester consisting of 40 mol%p-hydroxybenzoic acid and 30 mol% isophthalic acid/30 mol% hydroquinone (HIQ40), prepared by two different synthetic routes (“acidolysis” or “phenylester”) was studied by differential scanning calorimetry and X-ray diffraction. All these samples show a glass transition temperature in the range of 125–141°C, dependent on the sample thermal history. A crystal to nematic transition is observed between 300 and 375°C. The samples prepared by the acidolysis route, when compared to those producedvia the phenylester reaction, have higher crystallinity which is due to the formation of “IA/HQ” crystals. The crystallinity can be increased significantly (as much as twice) by annealing the polymers at 300°C. The heat of fusion (X → N, crystal to nematic) of the annealed acidolysis samples is also higher than that of the polymers prepared by the phenylester process. The nematic to isotropic (N → I) transitions are broad, exhibiting no definite clearing points. Several mesogenic transitions as suggested by X-ray studies and two crystallization peaks were found for all samples studied. This may be an indication that the samples consist of two, distinct polymeric compositions or that there are two crystal forms. Furthermore, since the intensity ratio of the two crystallization peaks changes as a function of annealing, it is clear that the chemical/physical state of the polymer depends on the thermal history of the samples. Attempts to prepare amorphous HIQ40 and nematic HIQ40 glass by quenching from the isotropic state (480°C and 400°C, respectively) were unsuccessful, however, it can be prepared by precipitation of the acidolysis polymer from solution.

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This paper is concerned with an analysis of the thermodynamics and kinetics of mesophase formation by cooling from the isotropic state of side-chain liquid crystalline polycarbosilanes containing spacers in the range from 3 to 11 CH2-groups. The polymers are characterized by their thermotropic behaviour as far as temperature, enthalpy and entropy of the transitions are concerned. The kinetics was followed by optical and calorimetric methods. Longer spacer length leads to more perfect ordering in the mesophase, higher isotropization temperatures, and lower glass transition temperatures. The Avrami and Ozawa formalism to describe the transition kinetics to the mesophase from the isotropic state cannot be interpreted as the nucleation and growth mechanism known from crystallization.

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Abstract  

Phase transition process of PEOm-b-PMA(Az)n was investigated by the simultaneous DSC-XRD measurement using the synchrotron radiation facility. Four endothermic DSC peaks were observed during heating process. These DSC peaks were assigned to the melting of PEO, the transition from SmX, which is a mixture of super-cooled SmC and crystal, to SmC, from SmC to SmA, and from SmA to isotropic liquid state as determined by XRD profiles. In SmC phase, the liner expansion coefficient calculated from the spacing variation of the smectic layer distance was larger than that of the other phases. This result reflected the fact azobenzene moieties in the long-side chains of PMA(Az)n forming the smectic layers and then they were tilted and stood up during the heating process.

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Thermally induced reorganization in LCP fibers

Molecular origin of mechanical strength

Journal of Thermal Analysis and Calorimetry
Authors: C. Saw, G. Collins, J. Menczel, and M. Jaffe

Abstract  

The molecular reorganization occurring in liquid crystalline polymer fiber during heat treatment is of great interest for many commercial reasons. Using thermal analysis techniques, WAXS and real time temperature dependent synchrotron SAXS, the structure and morphology of commercial LCP (liquid crystalline polymer), Vectran®, HBA/HNA (p-hydroxybenzoic acid/6-hydroxy-2-naphthoic acid), and its variant polymer fiber COTBP, HBA/HNA/BP/TA (BP-benzophenone, TA-terephthalic acid), have been examined. Both fibers have the typical liquid crystalline polymer structure, i.e., highly aligned with aperiodic sequencing along the fiber axis. There is a three-fold increase in strength in both fibers with heat treatment; however, the modulus is observed to increase significantly in COTBP but not in Vectran®. This paper reports on the changes and the differences on the structural and morphological behavior for both the as-spun and heat-treated LCP fibers. We propose an ‘oriented entanglement’ model to describe the differences between the two polymer fibers.

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Abstract  

Thermoanalytical studies on specialty polymers in Japan are reviewed. The basic and applied researches for the developments of new specialty polymers such as high-performance polymers, liquid crystalline polymers, and biodegradable polymers during the 1990's are introduced from the standpoint of thermal analysis. Many studies were performed for the improvements of durability and thermal stability of engineering polymers, biodegradable polymers and so on. A special topic of researches on the thermal behavior of polymers by high-pressure differential thermal analysis is included in this review.

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Abstract  

Phase transition process of polyester from phenanthrene, poly(oxyheptamethyleneoxy-2,7-phenantrenedicarbonyl), a main chain type liquid crystalline polymer, was investigated by simultaneous DSC-XRD measurements using the synchrotron radiation facility (PF). Three exothermic DSC peaks were observed during cooling from the isotropic liquid state. These DSC peaks were assigned to the transition from the isotropic liquid to the smectic A, that from the smectic A to C, and that from the smectic C to the crystalline state, respectively, as determined by XRD profiles. The rate of transition from the smectic A to C was very slow compared with the liquid crystalline transition and the crystallization. From the DSC-XRD results, the thermal expansion along c-axis in the crystal and smectic phases are 4.110−4 and 1.410−3 nm K−1 , respectively.

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