Commercial liquid crystal polymer

Figure 7.1 A range of the components from which most commercial liquid crystal polymers are synthesized.

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. 

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

Low molecular mass compounds capable of forming liquid crystals have been known since the late 1880s. They did not assume commercial importance until the late 1960s, however, when their properties were exploited in the design of electronic displays. Following the development of commercial applications for liquid crystals, polymers began to be studied for their potential in this application. 

Liquid crystalline solutions as such have not yet found any commercial uses, but highly orientated liquid crystal polymer films are used to store information. The liquid crystal melt is held between two conductive glass plates and the side chains are oriented by an electric field to produce a transparent film. The electric field is turned off and the information inscribed on to the film using a laser. The laser has the effect of heating selected areas of the film above the nematic-isotropic transition temperature. These areas thus become isotropic and scatter light when the film is viewed. Such images remain stable below the glass transition temperature of the polymer. 

Liquid crystal polymers have created a great deal of interest in recent years finding a number of commercial applications ranging from high-strength engineering plastics to optical display devices. A liquid crystal molecule possesses anisotropy and, as a mobile fluid, can spontaneously order. It therefore exhibits some of the properties of a liquid (mobility, flow) as well as a degree of order usually associated with a crystalline structure. 

S. L. Kwolek, a woman scientist of DuPont, invented the liquid crystal aromatic polyamides which eventually paved the way to the first commercial liquid crystalline polymer product—poly-p-phenyleneterephthalamide under the trade name Kevlar. She recently recalled, When I dissolved the PBA (poly-p-aminobenzamide) polymer at 10% concentration in tetram-ethylurea with 6.5% LiCl, the solution was unusually fluid, turbid, stir-opalescent, and butter-milk-like in appearance. The fiber that was spun turned out to be extremely strong with a modulus of 430 gpd This discovery in 1964 remains a milestone of this field. In recognition of her contribution, the American Society of Chemistry Industry awarded Kwolek the 1997 Perkin Medal. 

The miniaturization of PCBs has created the need for connectors to be made fi-om special materials suitable for shaping into thinner parts that can be packed into higher-destiny spaces and that can withstand higher soldering temperatures. Such materials available on the market include tailored grades of polyphenylene sulfide (PPS), PEEK, PET, polyetherimide, sulfone-based alloys, and liquid crystal polymers. Well-known commercial products are Rynite FR-530 and FR-945 modified PET grades of Du... 

The polymerisation processes described in the previous section are the classical processes used for producing the bulk commercial polymers. Newer processes have been and are being developed with a variety of aims in mind. These involve the production of novel polymer topologies (see box) precise control over chain length and over monomer sequences in copolymers control of isomerism (see section 4.1) production of polymers with special reactive end groups, the so-called telechelic polymers, production of specially designed thermally stable polymers and liquid-crystal polymers with a variety of different structures and properties. Other developments include the production of polymers with very precisely defined molar masses, and of networks with precisely defined chain lengths... 

Table 16.7 Examples for Commercially Available Liquid Crystal Polymers...

The selective alkylation of biphenyl and naphthalene is also possible, and is of commercial interest because 4,4 -diisopropylbiphenyl and 2,6-diisopropyl-naphthalene are used in the synthesis of speciality chemicals, for example for application as liquid crystal polymer materials for displays. For these larger molecules, large-pore zeolites such as mordenite give the best performance for isopropylation of naphthalene, introducing shape selectivity to linear (or more linear) dialkylated products over dialkylated products. 

Interest, academic and Industrial, In Liquid Crystal Polymers (LCP s) was sparked by the commercialization of Kevlar aromatic polyamide fiber In the early 1970 s. [1,2] This fiber can be made almost as stiff and as strong as steel, at one fifth of the density of steel. In addition. It has good resistance to chemical attack and outstanding resistance to heat. From a scientific point of view, LCP s are Interesting because they. In addition to displaying a variety of phenomena and properties seen with conventional Isotropic polymers, also exhibit many of the complex physical properties of small molecule liquid crystals.[3]... 

A related application requiring a two-phase treatment is that of polymer dispersed liquid crystals. The optical properties of these films may be electrically modulated and their potential for application is quite high (189). By controlled cooling, the size of the liquid crystal droplets in the polymer matrix may be varied between 1 and 30 )um or larger. Three commercial liquid crystals were dispersed in two thermoplastics [poly(vinylpyrrolidone) and poly(methyl methacrylate)] and epoxy. These were studied by infrared microspectroscopy, both polarized... 

Commercially available liquid crystal polymers (LCPs) (e.g., Vectra and Kevlar) exhibit excellent chemical resistance, low flammability, high elastic modulus, and low expansivity (depending on the mainchain orientation... 

---