Liquid crystal polymers thermotropic

Differences in LCP chemistry and performance do exist among different materials. Generalizations concerning characteristics are based on commercially available information, although it is anticipated that future commercial products may exhibit different properties. 

The chemical structures and characteristic morphology of LCPs lead to a combination of attractive features high strength, modulus and impact 

On a worldwide basis, close to 20 companies have LCP development programmes ranging from laboratory screening to full commercial sales [2]. As Table 7.1 illustrates, a broad range of companies are involved. The world market for LCPs is expected to reach at least 8 200 tonnes by 1997, reflecting an annual growth rate of at least 25% from 1987 - more than 

Hoechst Celanese Polyplastics Mitsubishi Chemical Mitsubishi Gas Co. Sumitomo Chemical Teijin Toray Toyobo Ueno Unitika 

The first commercially available material was Xydar LCP, manufactured by Dart and Kraft in late 1984. It is based on hydroxybenzoic acid, terephthalic acid and biphenol, and exists in a nematic structure. High-temperature performance is its outstanding property, as illustrated by the Tupperware line of Xydar-based Ultra 21 cookware. 

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D. Aciemo and M. R. Nobile, Thermotropic Liquid Crystal Polymer Blends, (F. P. La Mantia, ed.), Technomic Publishing, Lancaster (1993). 

Kevlar has the highest tensile strength and is often used as a reinforcing fibre in composites with, e.g., epoxy, PEEK. The thermotropic liquid crystal polymer Vectran is made by melt polymerisation of p-acetoxybenzoic acid and 6-acetoxy-2-naphthoic acid, (the corresponding hydroxy acids decompose on melting). Because of its liquid crystal properties the polymer can be spun into fibres from the melt. Kevlar is spun from a solution in concentrated sulfuric acid, and can be melt drawn to give a high modulus (stiff) polymer. Vectran ... 

Thermotropic Liquid Crystal Polymer Reinforced Polyesters... 

It was, however, observed that such systems under appropriate conditions of concentration, solvent, molecular weight, temperature, etc. form a liquid crystalline solution. Perhaps a little digression is in order here to say a few words about liquid crystals. A liquid crystal has a structure intermediate between a three-dimensionally ordered crystal and a disordered isotropic liquid. There are two main classes of liquid crystals lyotropic and thermotropic. Lyotropic liquid crystals are obtained from low viscosity polymer solutions in a critical concentration range while thermotropic liquid crystals are obtained from polymer melts where a low viscosity phase forms over a certain temperature range. Aromatic polyamides and aramid type fibers are lyotropic liquid crystal polymers. These polymers have a melting point that is high and close to their decomposition temperature. One must therefore spin these from a solution in an appropriate solvent such as sulfuric acid. Aromatic polyesters, on the other hand, are thermotropic liquid crystal polymers. These can be injection molded, extruded or melt spun. 

Matrix polymer and an electrically conducting thermotropic liquid-crystal polymer, LCP matrix PO, EPR, CPE, CSR, PS dispersed PANI, PAc, PPy, poly(3-undecylthiophene), poly(3-dodecylthiophene), or polyparaphenylene Ho Levon, 1995... 

The interest of 2,6-dialkylnaphthalenes as starting materials in the production of polyester fibers and plastics with superior properties [1, 2] and of thermotropic liquid crystal polymers [3] is clearly shown by the increasing number of recent patents relevant to their preparation and separation[3.5]. However, the selective formation of 2,6-dialkylnaphthalenes is not obvious, not only with conventional Friedel-Crafts catalysts [6-8], but also over solid catalysts such as silica-alumina [9-11] or zeolites. 

Shibaev, V.P. Freidzon, Ya.S. Kostromin, S.G. Molecular Architecture and Structure of Thermotropic Liquid Crystal Polymers with Mesogenic Side Groups Shibaev, V.P. Freidzon, Ya.S. Kostromin, S.G., Ed. Springer-Verlag New York, 1994, pp 77-120. 

Main-Chain Thermotropic Liquid Crystal Polymers... 

Thermotropic liquid crystal polymers (LCI ) are of considerable current interest, because of their theoretical and technological aspects [1-3]. Evidently, a new class of polymers has been developed, combining anisotropic physical properties of the liquid crystalline state with diaracteristic polymer features. This unique combination promises new and interesting material properties with potential ai lications, for example in the field of high modulus fibers [4], storage technology, or non-linear optics [5]. 

FIGURE 5.4 Examples of thermotropic liquid crystal polymers showing multiphase transitions (a) main-chain polymer (b) side-chain polymer. 

Copolymerization reactions can use many other combinations, but one interesting reaction involves the modification of poly(ethylene terephthalate) by reacting the preformed polymer with -acetoxybenzoic acid. This has the effect of introducing a mesogenic unit to the structure at the points where the two units combine, producing a thermotropic liquid crystal polymer with a flexible spacer. 

P. Magagnini in Thermotropic Liquid Crystal Polymer Blends (Ed. F. P. la Mantia), Technom-ic, Basel 1993, p. 1. 

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