Crystals liquid crystal polymers

Keywords Hydrogen bonding. Liquid crystal. Liquid crystal polymer. Self-assembly, Selforganization, Complex, Gel, Supramolecular chemistry... 

PLC Polymer liquid crystal (liquid crystal polymer, ISO 1043-1 LCP) ... 

Keywords Chain conformation Cholesteric Elastomer Liquid crystal Liquid crystal polymer Nematic Polymer networks Smectic... 

Liquid crystal polymers are also used in electrooptic displays. Side-chain polymers are quite suitable for this purpose, but usually involve much larger elastic and viscous constants, which slow the response of the device (33). The chiral smectic C phase is perhaps best suited for a polymer field effect device. The abiHty to attach dichroic or fluorescent dyes as a proportion of the side groups opens the door to appHcations not easily achieved with low molecular weight Hquid crystals. Polymers with smectic phases have also been used to create laser writable devices (30). The laser can address areas a few micrometers wide, changing a clear state to a strong scattering state or vice versa. Future uses of Hquid crystal polymers may include data storage devices. Polymers with nonlinear optical properties may also become important for device appHcations. 

Chemical Resistance of LGPs. Ceitain liquid crystal polymers (eg, Vectra) have extremely high chemical resistance to a variety of aggressive chemicals and solvents. Table 18 shows the chemical stabiUty of Vectra test-bars to various agents (244). 

NHydroxyben2oic acid is of significant commercial importance. The most familiar application is the use of several of its esters as preservatives, known as parabens. Also of interest is the use in liquid crystal polymer applications. 

A very high, price and performance family of polymers called liquid crystal polymers (LCPs) exhibit extremely high mechanical and thermal properties. As their ease of processing and price improve, they may find appHcation in thin-waH, high strength parts such as nails, bolts, and fasteners where metal parts cannot be used for reasons of conductivity, electromagnetic characteristics, or corrosion. 

The liquid crystal polymers consist of rod-like molecules which, during shear, tend to orient in the direction of shear. Because of the molecular order the molecules flow past each other with comparative ease and the melts have a low viscosity. When the melt is cooled the molecules retain their orientation, giving self-reinforcing materials that are extremely strong in the direction of orientation. 

Crystalline polymers primarily of interest as fibres, including some grades which may be considered as liquid crystal polymers. 

The Kevlar polymer may be regarded as a liquid crystal polymer (see Chapter 25) and the fibres have exceptional strength. They are thus competitive with glass, steel and carbon fibres. 

Yet another recent development has been the alloying of polycarbonates with liquid crystal polymers such as Vectra (see Section 25.8.1). These alloys are notable for their very good flow properties and higher strength and rigidity than conventional bisphenol A polycarbonates. 

Figure 25.24. Difference in behaviour between liquid crystal polymers and conventional crystalline polymers in the melt at rest, during shear and when cooled after shearing...

Figure 25.25. Typical sequences found in intractable liquid crystal polymers with >400°C...

It was estimated that in 1987 about 25 companies were involved in the development of liquid crystal polymers, but by 1995 only Hoechst and Amoco were sharing the 3000 t.p.a. global market in the ratio of about 70 30. 

Over the years polymers have been produced suitable for use at progressively higher temperatures. Where this is a requirement, it is usual first to decide whether a rubbery or a rigid material is required. If the former, this has been dealt with by the author elsewhere." If the latter, it is usually convenient to look in turn at polycarbonates, PPO-based materials, polyphenylene sulphides, polysul-phones, polyketones such as PEEK and PEK, polyamide-imides, poly-phthalamides, fluoropolymers, liquid crystal polymers and polyimides. 

Liquid crystal polymers Cross-linked Structures Polyblends... 

Liquid crystal polymers (LCP) are a recent arrival on the plastics materials scene. They have outstanding dimensional stability, high strength, stiffness, toughness and chemical resistance all combined with ease of processing. LCPs are based on thermoplastic aromatic polyesters and they have a highly ordered structure even in the molten state. When these materials are subjected to stress the molecular chains slide over one another but the ordered structure is retained. It is the retention of the highly crystalline structure which imparts the exceptional properties to LCPs. 

Figure 13 Schematic diagram of the dependence of <7 on pressure. (F) Denotes folded-chain nucleus, (B) denotes bundle-like nucleus and (B ) denotes addition of ethyl cellulose liquid crystal polymer. (From Refs. 104, 110, 111, and 117.)...

Linear chain polymers with repeating sequences of hard and soft segments Possibility of formation of liquid crystal polymers and thermoplastic elastomers... 

N. A. Plate (ed.). Liquid Crystal Polymers, Plenum Press, New York (1993). 

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

Muller, K., Kothe, G., and Wassmer, K.-H. Dynamic Magnetic Resonance of Liquid crystal Polymers Molecular Organization and Macroscopic Properties. Vol. 95, pp. 1 — 56. 

High-temperature TPs are available to compete with TSs, metals, ceramics, and other nonplastic materials. The heat-resistant TPs include polyetheretherketone (PEEK) and polyethersulfone (PES), polyamideimide, liquid crystal polymer (LCP) and others. 

Liquid crystal polymer (LCP) Excellent Commercial LCPs excellent natural LCPs not stable. 

DuPont Acetal EVA Nylon 6, 6/6, 6/12, Mineral Filled 6/6, Industrial PBT PET Polyethylene Modified Thermoplastic Elastomer Ionomer Liquid Crystal Polymer ... 

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