All-aromatic liquid-crystalline

All-Aromatic Liquid-Crystalline Polyesters of Phenylhydroquinone with Ether and Ketone Linkages... 

It is instructive to compare the melt viscosities of an all-aromatic liquid crystalline polyester with those of a similar polyester that is not liquid crystalline because of kinks in the polymer chain. Figure 7 compares the melt viscosities at 360 C of the polyterephthalate and polyisophthalate of phenylhydroquinone at the shear rates which are employed in melt processing (about 1000 sec for melt spinning and about 10,000 sec" for injection molding). The polyterephthalate has the low melt viscosities that are typical of liquid crystalline... 

In a study of the effects of temperature on the melt viscosities of copolyesters of terephthalic acid, i sophthalic acid, and methylhydroquinone, McFarlane and Davis observed that minima in the melt viscosity versus temperature curves occurred at about 340 to 360°C in compositions containing 40 to 60 mol % isophthallc acid (total diacids equal 100 mol %). The increase in the melt viscosities with increasing temperature after the minima presumably is due to the Increase in the isotropic content of the polymers and the decrease in the degree of liquid crystallinity. We did not observe this phenomenon in the rigid-rod, all-aromatic, liquid crystalline polyesters that did not contain any meta component because of the high temperatures involved (above the decomposition temperatures of the polyesters). A poly(terephthalate-Isophthalate) of methylhydroquinone containing 70 mol % isophthallc acid was not liquid crystalline and, therefore, did not exhibit a minimum in a plot of melt viscosity versus temperature... 

The lowest cost process for preparing all-arcmatic liquid crystalline polyesters involves the reaction of aromatic carboxylic acids with acetates of aromatic hydroxy ocnpounds a recent history (2) describes the development of these ICP s. Because aoetic acid is evolved in the process and reaction temperatures are above 300°C, expensive corrosion-resistant reactors must be installed for ccranercial production. In cur latest paper (2) of this ICP series, we described a number of aliphatic-aromatic ICP s which can be produced in conventional polyester reactors and injection molded to give plastics with very high mechanical properties, heat-deflection temperatures (HDT s), and solvent resistance. These ICP s (la) were prepared by the reaction of the dimethyl ester of... 

Lee, W. and Chang-Chien, G., All-hydrocarbon liquid crystalline polysiloxane polymer as stationary phase in gas chromatography capillary column for separation of isomeric compounds of polynuclear aromatic hydrocarbons. Anal. Chem., 70, 4094-4099, 1998. 

PEN). This article also covers the increasingly commercially important high performance liquid crystalline all-aromatic polyesters, eg, Vectra [70679-92-4/, [82538-13 4] andXydar [31072-56-7]. 

The source of all carbon relevant to the present context is the feedstock of hydrocarbon molecules (aliphatic, aromatic, with and without heteroatoms). Figure 10 summarizes the possibilities for their conversion into black carbon. The chemical route comprises polymerization into aromatic hydrocarbons with final thermal dehydrogenation. This process often includes a liquid crystalline phase immediately before final solidification. In this phase large aromatic molecules can sclf-organizc into parallel stacks and form well-ordered precursors for graphitic structures with large planar graphene layers. This phase is referred to... 

Although studies concerning main chain liquid crystalline polymers were originated by Onsager (la) and Ishihara (lb) in the late 1940 s, extensive work in this field did not really begin until the early 1970 s. Jackson and Kuhfuss (2) reported the first thermotropic polyester by modifying polyethylene terephthalate with various amounts of p-hydroxybenzoic acid (HBA). They found that the copolyester with HBA content of at least 35 mole % have opaque melts. Subsequent studies in the area of aromatic polyesters by various authors resulted in a large number of patents and publication. (3.) These polymers were all derived from unsubstituted and... 

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