Thermotropic LCPs crystal polymer

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 PATs used were Torlon 4000Tf-40 (PAI-1) and Torlon 4203L (PAI-2) supplied by Amoco Performance Products. The thermotropic liquid crystal polymer (LCP) used was Vectra A950, which is a random copolyester delivered fi om HBA-HNA (Hoechst Celanese). The PAl-1 was in fine powder form with no additives while the PAI-2 was in pellet containing 0.5% PTFE and 3% TiOj. 

In general, LCPs can be classified as Thermotropic Liquid Crystal Polymer (TLCP) and Lytropic Liquid Crystal Polymer. Liquid Crystal Polymers (LCPs) whose phase transitirm to the liquid crystalline phase occurs due to change in temperature, are called thermotropic liquid crystal while a phase transition by changing the polymer concentration in a solvent (as well as temperature) is called lyotropic liquid crystal (Brostow 1992). 

The industrial development of thermotropic liquid crystal polymer (LCP) materials can be traced from its theoretical origins, through the identification of useful compositions, to full commercialization. The future industrial challenge will be to define and develop applications which take advantage of the unique properties of these materials. 

Liquid crystalline polymers (LCPs), 10 374, 517-518 13 370-372. See also Liquid-crystal polyesters (LCPs) Liquid-crystal polymers (LCPs) thermotropic, 13 381-382 Liquid-crystalline thermotropic polyesters, 20 34... 

Liquid crystal polymers (LCP) are polymers that exhibit liquid crystal characteristics either in solution (lyotropic liquid crystal) or in the melt (thermotropic liquid crystal) [Ballauf, 1989 Finkelmann, 1987 Morgan et al., 1987]. We need to define the liquid crystal state before proceeding. Crystalline solids have three-dimensional, long-range ordering of molecules. The molecules are said to be ordered or oriented with respect to their centers of mass and their molecular axes. The physical properties (e.g., refractive index, electrical conductivity, coefficient of thermal expansion) of a wide variety of crystalline substances vary in different directions. Such substances are referred to as anisotropic substances. Substances that have the same properties in all directions are referred to as isotropic substances. For example, liquids that possess no long-range molecular order in any dimension are described as isotropic. 

Two types of liquid crystal polymers (LCP s) can be distinguished lyotropic and thermotropic. The first type is formed in a solution this is done when the polymer has such a high melting point (low AS, see 4.2), that it cannot be handled in the molten condition without being degraded. If this limitation is not present, then the orientation can be brought about in the melt in such a case we have a thermotropic LCP. 

Both thermotropic and lyotropic liquid crystal polymers exhibit characteristic features with regard to their microstructureJ Anisometrical monomers such as rods or discs are connected to chains in an appropiate manner. These anisometrical monomers are considered to be the mesogens and may be part of main chain LCP, side chain LCP, or of both types together (Fig. 6). Between the mesogens are located flexible spacers of non-mesogenic character. Sufficient flexibility is a prerequisite for liquid crystal formation, with an increase in either temperature or solvent concentration. 

More recently,thin walled articles have been fabricated by blow-molding composites of liquid crystal polymer (LCP) and expanded porous polydetrafluoroethylene sheetingl l material. Container application examples include food and pharmaceuticals, automotive gas tanks, bottles, and other vessels. Unlike most other thermoplastic polymers, thermotropic LCP forms high-viscosity melts that have thixotropic characteristics. Applying shear force to the melt substantially alters the melt viscosity of LCP and the orientation of its polymer domains. These attributes are useful to... 

Many unique LCP characteristics come from this structure. LCP is also classified into thermotropic and lyotropic LCP, just as conventional polymers, namely thermoplastics and thermoset. Thermotropic LCP corresponds to thermoplastics because it reveals its liquid crystal nature in the molten stage. 

Liquid Crystal Polymers (LCP) This novel polymeric family excels in thermal and mechanical performance. The uniqueness of these polymers stems from the extraordinary crystalline stmcture, exhibiting ordered domains even in the liquid state. These are chainlike macromolecules of rigid structure, mainly because of the existence of aromatic rings such as aromatic polyamides and polyesters. There are two major groups—lyotropic and thermotropic. In the former group, the liquid crystals are formed in an appropriate solution, usually forming fibers (like Kevlar , that appeared in 1965 as an aramide). 

Liquid crystal polymers (LCPs) were introduced over the last three decades. In the liquid state, either as a solution (lyotropic) or a melt (thermotropic), they lie between the boundaries of solid crystals and isotropic liquids. This polymeric state is also referred to as a mesomorphic structure, or a mesophase, a combined term adopted from the Greek language (mesos = intermediate morphe = form). This state does not meet all the criteria of a true solid or a true liquid, but it has characteristics similar to both a solid and a liquid. For instance, the anisotropic optical properties of LC polymeric fluids are like those of crystalline solids, but their molecules are free to move as in liquids. 

SINCE the discovery of liquid crystalline phenomenon for low molecular weight liquid crystals (LMWLCs) more than 100 years ago, anisotropic ordering behaviors of liquid crystals (LCs) have been of considerable interest to academe [1-8], In the 1950s, Hory postulated the lattice model for various problems in LC systems and theoretically predicted the liquid crystallinity for certain polymers [1-3], As predicted by the Hory theory, DuPont scientists synthesized lyotropic LCPs made of rigid wholly aromatic polyamide. Later, Amoco, Eastman-Kodak, and Celanese commercialized a series of thermotropic main-chain LCPs [2]. Thermotropic LCPs have a unique combination of properties from both liquid crystalline and conventional thermoplastic states, such as melt processibility, high mechanical properties, low moisture take-up, and excellent thermal and chemical resistance. Aromatic main-chain LCPs are the most important class of thermotropic LCPs developed for structural applications [2,4-7]. Because they have wide applications in high value-added electronics and composites, both academia and industry have carried out comprehensive research and development. 

A disadvantage of Kevlar is that the polymer Is a "lyotropic" liquid crystal, that Is, one that becomes liquid crystalline when dissolved In an appropriate solvent. The need to remove solvent during the fabrication process limits lyotropic LCP s to formation of thin fibers or films. In order to Form thick articles or parts with more complicated shapes requires a "thermotropic" LCP, that Is, one that becomes liquid crystalline upon heating.[4]... 

Liquid crystalline polymers are termed liquid crystal from the fact that the polymers exhibit crystalline properties as a liquid. In LCPs there is little entwining of molecules. LCPs are polymers having a degree of molecular order either in solution (lyotropic) or in a melt (thermotropic) intermediate between those of a solid crystals and those of isotropic liquids and are called liquid crystalline. Most... 

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