Liquid Crystalline Polymers LCP

Liquid crystalline polymers are the polymers which combine both LC properties and polymer properties. Basically, a rigid polymer is expected to exhibit LC phases even in melt state. The rigid unit can be attached to both main chain and side chain and the polymers are 

From thermod)mamic consideration, the LC phase in equilibrium with the crystal may be the LC phase with long rage orientational order and affects very little on AS and AH. The crystalline 

In 1926, United States-based E.I. du Pont de Nemours and Co. initiated research in the field of very large molecules and synthetic fibers. This early research, headed by W.H. Carothers, concentrated on polymer which became nylon, the first synthetic fiber. Soon after, in the years 1939 1, John Rex Whinfield and James Tennant Dickson, employees of the Calico Printer s Association of Manchester, patented polyethylene terephthalate (also called PET or PETE) in 1941. Polyethylene terephthalate is the basis of synthetic fibers such as polyester, dacron, and terylene. In 1946, du Pont purchased the right to produce this polyester fiber in the United States. The company conducted some further developmental work, and in 1951, began to market the fiber under the name Dacron. Dupont s polyester research led to a whole range of trade-marked products, such as Mylar (1952), which is an extraordinarily strong polyester (PET) film, and others. 

During the following years, several companies became interested in polyester fibers and produced their own versions of the product for different uses. Polyesters are synthesized from chemicals found mainly in petroleum and are manufactured in the form of fibers, films, and plastics. 

Polyester also refers to the various polymers in which the backbones are formed by the esterification condensation of polyfunctional alcohols and acids . Polyester can also be classified as saturated and unsaturated polyesters. Saturated polyesters refer to the family of polyesters in which the polyester backbones are saturated. They are thus not as reactive as unsaturated polyesters. The linear, high molecular weight polymer works as a thermoplastic, such as polyethylene terephthalate (Dacron and Mylar). The common reactants for making saturated polyesters are a glycol and an acid or anhydride. 

Conventional liquids - those of low-molecular-weight materials as well as those formed by polymers - do not exhibit any order they are amorphous or isotropic. However, in some specific cases so-called liquid-crystalline mesophases are 

In main chain LCPs the mesogens are part of the polymer backbone, while side chain LCPs are formed when the mesogens are connected as lateral substituents to the polymer, in most cases via a flexible spacer . Also, combinations of main chain and side chain LCPs are known. 

LCP phases are subdivided into thermotropic or lyotropic. Lyotropic liquid crystals are formed by macromolecules that show liquid crystalline behavior in solution. This behavior is strongly concentration dependent. Thermotropic liquid crystals are molecules that show liquid crystalline behavior above the melting point of their crystallites. 

Like their low-molecular-weight analogs, LCPs display characteristic colored textures in polarized light. Thus, the opalescence of lyotropic polyaramides in solution can be viewed with the naked eye. For thermotropic polymers the birefringence of the anisotropic melt is often easily detectable in a polarizing microscope. 

If the mesogens are pendant to the polymer backbone, materials are obtained with special magnetic, electrical, and optical properties. They provide for nonlinear optics (NLOs) applications in numerous optoelectronic elements. 

The molecular structure of liquid crystalline polymers is one of their characteristic features. It comprises rigid, rod-like macromodules which align in the melt to produce liquid structures. Although more expensive than some competing polymers, LCP possess better flow characteristics to fill the thin walls of modern connectors, for example. 

Solvay Advanced Polymers states that its XYD AR LCP, which may be reinforced with glass, glass/mineral or just mineral filled, has the highest heat deflection temperature (HDT) of any thermoplastic, with an inherent resistance to virmally all chemicals together with unmatched processing capability. 

LCP are fully aromatic copolyesters or copolyesteramides which have become the standard high performance polymers used in certain new electrical/electronic applications notably fuel cells. Thermosetting LCP are also available. 

A = Excellent resistance less than 2 % change in weight and dimensions, less than 5% change in mechanical properties, such as elastic modulus, flexural strength, and hardness 

Ta bl e A. 3 8 Chemical resistance of LCP (testing conditions immersion of 5 specimens (127 12.7 3.2 mm) no external bad changes in weight and dimension, elastic modulus, and hardness were measured), GF=glass fibers, M = mineral, MF = mineral fiber, S = standard, HT=high temperature, HM = high modulus, RL = Reflow-solder resistant [695] (Continued) 

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Another natural polymer that needs a fresh look into its structure and properties is bitumen [123], also called asphaltines, that are used in highway construction. Although a petroleum by-product, it is a naturally existing polymer. It primarily consists of polynuclear aromatic and cyclocaliphatic ring systems and possesses a lamellar-type structure. It is a potential material that requires more study, and high-performance materials such as liquid crystalline polymer (LCP) could be made from it. 

Blends of polypropylene (PP) and liquid crystalline polymer (LCP) processed without melting the LCP were compared with conventional melt processed blends. In a first stage, PP was blended with 20 wt% of LCP in a twin-screw extruder with the take-up speed varied to achieve blends with different LCP fiber dimensions. In the second stage, these blends were processed both below and above the Tm of the LCP by extrusion and injection molding. 

A block copolymer composed of liquid crystalline polymer (LCP) segments or that composed of segments having an LCP unit in their main chain or side chain was synthesized [67,68]. The latter showed partial compatibility and second-phase separation even when in a melt liquid crystalline state. 

Liquid crystalline polymers (LCPs) are best thought of as being a separate, unique class of TPs. Their molecules are stiff, rodlike... 

TABLE 2.14 Schematic Representation of Three Main Categories of Liquid Crystalline Polymers (LCPs)... 

Liquid crystalline polymers (LCPs), 49 melt rheology of, 52 Liquid crystalline (LC) state, 48-49 Liquid crystalline thermotropic polyesters, 20... 

Liquid crystal phases, 15 100 Liquid-crystal polyesters (LCPs), 10 191-192 20 38-39 manufacture of, 20 44-45 Liquid-crystal polymers (LCPs), 15 110 20 3, 78-86, 398. See also Liquid crystalline polymers (LCPs) advantages of, 20 81... 

Research on liquid crystalline polymers(LCP) is a fashionable subject with the goal of developing speciality polymers of superior mechanical and thermal properties. Besides these properties, other interesting properties of LCP have not been fully utilized. We are trying to use thermotropic LCP for photon-mode image recording material. 

While no direct evidence of liquid crystallinity in PET-BB copolymers has been reported, the high-BB-content copolymers have been shown to possess morphologies similar to those of liquid crystalline polyesters [40], and show major changes in both melt relaxation times and fiber tensile moduli, suggestive of structural organization in a frustrated liquid crystalline polymer (LCP) (Table 6.3 and Figure 6.4) [41, 42],... 

By building - in combinations of aromatic rings into the polymer chains, chemists are able to produce polymer chains with very low chain flexibility. In the limit they reach rigid-rod-type op polymers. Such polymers show substantial temperature - pressure -concentration regions in which the stiff polymer chains arrange in some form of orientation. This phase behaviour gave them the name Liquid Crystalline Polymers (LCP) and LCP have unique properties. 

Liquid-crystalline polymers (LCP) can be used in thermoset systems as initially miscible modifiers that phase-separate during cure. 

There is no consensus yet as far as the name of these materials is concerned. Some investigators use the name polymer(ic) liquid crystals (PLCs), others call them liquid crystalline polymers (LCPs) or mesogenic macromolecules. 

Liquid crystalline polymers (LCPs) have gained attraction as materials with interesting optical, mechanical and rheological properties [3-7]. This review summarizes research on thermotropic liquid crystalhne polymers synthesized by metathesis routes, as this chemistry has proven to be a versatile way to build up well-defined polymer architectures [8]. Recent results promise to ejq)and the possible uses of these methods. 

Finally, there are complex fluids that are intermediate between solid and liquid in more than one of the ways listed above. Liquid crystalline polymers (LCPs) are both viscoelastic and liquid crystalline. Ordered block copolymers are viscoelastic and anisotropic. Glassy polymers possess long viscoelastic time scales both because they are glassy and because they are polymeric. Filled polymer melts possess the properties of both polymer melts and suspensions. 

An interesting class of condensation copolymers is the liquid crystalline polymers (LCP). From the viewpoint of practical applications, LCP are very attractive as... 

This chapter provides an overview of current researches on liquid crystalline polymers (LCPs). Topics include syntheses of main-chain and side-chain LCFs, structured characterization of LCFs and LCP networks and rheology and processing. Applications of LCP/polymer blends as self-reinforced polymers and electro-optical meterials are also discussed. 

Although the technical applications of low molar mass liquid crystals (LC) and liquid crystalline polymers (LCP) are relatively recent developments, liquid crystalline behavior has been known since 1888 when Reinitzer (1) observed that cholesteryl benzoate melted to form a turbid melt that eventually cleared at a higher temperature. The term liquid crystal was coined by Lehmann (2) to describe these materials. The first reference to a polymeric mesophase was in 1937 when Bawden and Pirie (2) observed that above a critical concentration, a solution of tobacco mosaic virus formed two phases, one of which was bireffingent. A liquid crystalline phase for a solution of a synthetic polymer, poly(7-benzyl-L-glutamate), was reported by Elliot and Ambrose (4) in 1950. 

Because the textures of liquid crystalline polymers (LCPs) are qualitatively similar to those of low molecular weight liquid crystals, they are interpreted in the same way. However, the microscopy of LCPs is less straightforward ... 

This paper presents summaries of unique new static and dynamic theories for backbone liquid crystalline polymers (LCPs), side-chain LCPs, and combined LCPs [including the first super-strong (SS) LCPs] in multiple smectic-A (SA) LC phases, the nematic (N) phase, and the isotropic (I) liquid phase. These theories are used to predict and explain new results ... 

The unique molecular packing of rod-like chains in liquid crystalline polymers (LCP) closely resembles the extended chain structure of highly oriented flexible chain polymers, suggesting that these materials are good candidates for barrier applications. Thermotropic LCP s, first developed in the early 1970 s, have been the object of much interest because of their excellent mechanical properties and ease of product fabrication. Preliminary observations have shown that a commercially available wholly aromatic thermotropic copolyester has gas permeability coefficients that are lower than those of polyacrylonitrile (4.). These results raise some fundamental questions as to the nature of the mechanism for transport of small molecules through a matrix of ordered rigid rod-like chains. 

Thermotropic liquid crystalline polymers (LCP) show during heating one or more mesophase transition effects before they change after an endothermic fusion maximum into an isotropic melt. These transition effects are usually indicated by Tm,... 

Toy et al. [1994] investigated the effect of irradiation on blends of liquid crystalline polymers (LCP) with either polyvinylidene fluoride (PVDF) or HDPE (Table 11.9) such blends are useful for making dimensionally recoverable articles. This patent contains many claims but few results. 

Specific blends, which could offer an interesting combination of properties with proper com-patibilization, include PPS/PSE, PEl/PPS, PA/PSE, PA/PEI, and PC/PPS. Patent activity has been noted for most of these blend combinations as well as other selected blends involving engineering polymers as noted in Table 17.3. A number of recent patent and published papers have discussed blends of engineering polymers with various specialty polymers including high temperature polymers, liquid crystalline polymers (LCP s), conductive polymers, and as matrix materials for molecular composites. These will be discussed in the following sections. 

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