Liquid crystal polymers , additive

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.)...

Pitches can be transformed to a mesophase state by further chemical and physical operations. Heat treatment of conventional pitches results in additional aromatic polymerization and the distillation of low molecular weight components. This results in an increase in size and concentration of large planar aromatic molecular species whereupon the precursor pitch is transformed to a mesophase state exhibiting the characteristics of nematic liquid crystals (1). Additional heat treatment converts the mesophase pitch to an infusible aromatic hydrocarbon polymer designated as coke. 

In addition to the opportunities for new materials synthesis and characterization along these lines, transport properties, rheology, and processing techniques for liquid crystal polymers are essentially unexplored. Experiences with synthesis of polymer structure based on these liquid crystal templates may open up other creative avenues for template synthesis, for example, inside other crystalline structures, chlathrates, or zeolites, or on surfaces [4], Composites, alloys, or mixtures of liquid crystalline and flexible polymers may produce new materials. 

Polyphosphazene synthesis provides additional possibilities for preparing liquid crystal polymers with different properties. As noted above, the substitution process (Figure 2) enables one to synthesize a wide variety of polymers. The phosphazene inorganic backbone Is a highly flexible polymer chain glass transition temperatures can... 

The other possibility for what is occurring in the melt is that the addition of component (2) destroys the domain structure of the copolymer. It has been proposed (21) that the domain structure of liquid crystal polymers is responsible for the shear-thinning behavior which is experimentally observed. Since the blends are less shear-thinning than the copolymer, it is suggested that the domain structure which is responsible for this effect has been broken up. This suggestion would indicate a certain miscibility in the melt which remains in the solid state. 

Block-like and segmented polymers represent chemically bound "multicomponent" systems that, in our opinion, are able to mimic some of the non-bonded interactions occurring in blends of either compatible or not compatible pol3nners, and to describe phenomena connected with phase segregation and the onset of peculiar micromorpho-logical properties. Additionally, liquid crystal polymers, even though "monocomponent" from a macrochemical point of view in that constituted of only one polymeric material, in reality do behave, under certain selected thermodynamic conditions, as mechanical mixtures of at least two components. 

Perhaps one of the most important applications of chiral induction is in the area of liquid crystals. Upon addition of a wide range of appropriate chiral compounds, the achiral nematic, smectic C, and discotic phases are converted into the chiral cholesteric (or twisted nematic), the ferroelectric smectic C and the chiral discotic phases. As a first example, we take the induction of chirality in the columns of aromatic chromophores present in some liquid-crystalline polymers. " The polymers, achiral polyesters incorporating triphenylene moieties, display discotic mesophases, which upon doping with chiral electron acceptors based on tetranitro-9-fluorene, form chiral discotic phases in which the chirality is determined by the dopant. These conclusions were reached on the basis of CD spectra in which strong Cotton effects were observed. Interestingly, the chiral dopants were unable to dramatically influence the chiral winding of triphenylene polymers that already incorporated ste-reogenic centers. 

Values for (AT) decrease from approximately 42°C to 24°C as the liquid crystal polymer content increases from 0 wt. % to 70 wt. % respectively. This indicates that as the level of the possible nucleating LC species is increased, the crystallization rate is apparently enhanced and hence a narrower (AT) is observed. This speculation is somewhat similar tg what Takayanagi et al. recently proposed f< j>jj the effect of Aramid surfaces on the crystallization of Nylon 6. In addition, the melting endotherm associated with... 

A polymer additive that is a side group liquid crystal polymer has been found to improve the switching speed of the system. Such a polymer is shown in Figure 17.8. 

Liquid crystal polymers are used in automotive, electrical, chemical processing, and houseWd applications. One application is for oven and microwave cookware. Because of their higher costs, the material is used only in applications where its superior performance justifies the additional expense. 

Synthetic thermosetting polymers used in the construction industry are polyester, vinylester and epoxies these materials are generally used to manufacture parts of the machines that produce sustainable energy generators. In addition, thermoplastic resins, such as polyetheretherketone (PEEK), polyethersulphone (PES) and various liquid crystal polymers (LCP) are also used. The latter high performance polymers also meet stringent out-gassing (relevant to space environments) and flammability requirements. 

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]... 

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