All-aromatic liquid-crystalline polyesters

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... 

All commercial separators so far have been made of polyolefins, but they provide only limited heat resistance. Research is now focusing on separators made of different materials which would offer superior heat resistance. These include heat-resistant rubber such as silicone mbber and fluororubber, aromatic polyamide resin, liquid crystalline polyester resin, heat-resistant resin containing polyoxyalkylene, and resin with cross-linked groups. Separators made of such materials are expected to demonstrate not only high temperature stability and safety but also superior ion transportation for better rate capability at high current discharge. 

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]. 

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... 

Thermotropic polyester backbone chemistry is characterized by a high degree of aromaticity, planarity, and linearity in the chain backbone. Most common moieties are p-phenylene, 1,4-biphenyl, and 2,6-naphthalyl moieties linked by ester or amide linkages. Polymers that form liquid crystal phases in the melt are thermotropic, whereas those that form liquid crystalline phases in solution are lyotropic. The all-aromatic polyester homopolymers tend to be intractable, decomposing at temperatures well below their melting points and insoluble in most... 

Goodman, McIntyre, and coworkers at ICI prepared polyesters by heating diacid chlorides with various substituted hydroquinones in an inert solvent at 200 to 300 C.2> Because of what we know now about the effect of composition on liquid crystallinity, the all-aromatic compositions prepared with s)nnmetric aromatic dlcarboxyllc acid chlorides, such as terephthaloyl chloride or substituted terephthaloyl chlorides, and substituted hydroquinones (substituents were CH3,... 

Schaefgen and coworkers disclosed the use of substituted hydroquinones for the preparation of thermotropic liquid crystalline all-aromatic polyesters and demonstrated that fibers, films, and plastics having high mechanical properties could be obtained on extrusion or molding. ... 

A film of the polyterephthalate of phenylhydroquinone was still creasable after 30 weeks, when the test was stopped, and our experience with other liquid crystalline all-aromatic polyesters containing no alkyl or halogen... 

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. 

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