Thermotropic aromatic poly

Work with NDA, OHN and HNA monomers has also led to the development of thermotropic aromatic poly(ester-amides). The question arose as to whether the introduction of hydrogen bonding capability into the chain might result in some useful property improvements. The greater interchain interaction could result in increased fiber fatigue resistance, higher filament Shear modulus (and tensile modulus) and improved fiber surface adhesion. Early data are promising, but considerable research remains before the potential of the ester-amide variants can be fully defined. 

Engberg and coworkers [14,98] investigated the blends of thermotropic PLCs with fully amorphous polymers polyethersulfone (PES), polycarbonate (PC) and aromatic poly (ester carbonate) (APEC) [98] and semicrystalline polymers like polybutylene terephthalate (PBT) [14]. aL was calculated according to the Takayanaga model [101] as follows ... 

Thermotropic aromatic copolyester fibers are produced by melt spinning since the combination of an aromatic backbone and flexible segments results in an LCP which can be melt processed. Copolyesters, such as p-hydroxybenzoic add (PHBA) modified poly(ethylene terephthalate) (PET), 60/40 PHBA/PET (X7G) polymers, have been produced by the Tennessee Eastman Company [425-427]. Other melt processable nematic thermotropic LCPs (TLCP), based on combinations of 2,6-naphthalene dicarboxylic add (NDA), 2,6-dihydroxynaphthalene (DHN) and 6-hydroxy-2-naphthoic acid (HNA), and referred to as Vectra LCP resins, have been conunercialized (trademark by Hoechst Celanese Corporation [406]). 

Thermotropic aromatic copolyesters i.e. polyObenzoate-naphthoate) and poly(naphthoate-aminophenol terephthalate) Vectra Vectran Hoechst Celanese Hoechst Celanese Fabricated parts, interconnects, connectors Fibers in sporting goods, sailcloth, bow strings. Films for printed circuit boards... 

Methods of synthesis of thermotropic polyesters, Poly-p-phenylene terephthalate and poly-p-hydroxybenzoate are the simplest and most accessible representatives of the aromatic polyesters ... 

RHEO-OPTICAL STUDIES OF THE THERMOTROPIC AROMATIC COPOLYESTERS OF POLY(ETHYLENE TEREPHTHALATE) AND />-ACETOXYBENZOIC ACID... 

Aromatic copolyesters which are sufficiently rigid to form a nematic mesophase upon heating (e.g. 4 and 5) also give HSHM fibres, but major industrial exploitation awaits improved competitiveness with established fibres. Exceptionally high strength values have been reported for fibres made from thermotropic nematogenic poly(azomethine)s (e,g, 6) but these materials seem to suffer from a poor hydrolytic stability. ... 

Working with a solution is needed for polymers which above their melting point would degrade (example aromatic polyamide fibres such as Kevlar and Twaron). For fibres the removal of the solvent is not too problematic. In e.g. injection moulding applications solvents caimot be used here thermotropic LCP s have to be used. Since these would degrade during processing, they are diluted by copolymerisation (example poly-hydroxy-benzoic acid - co - PETP)... 

Melt poly condensation is also the most popular method for other thermotropic condensation polymers, including the polyazomethines where the reaction between aromatic aldehydes or ketones and primary amines with elimination of water leads to azomethine (Schiffs base) formation 48). 

Stiff rod-like helical polymers are expected to spontaneously form a thermotropic cholesteric liquid crystalline (TChLC) phase under specific conditions as well as a lyotropic liquid crystal phase. A certain rod-like poly(f-glutamate) with long alkyl side chains was recently reported to form a TChLC phase in addition to hexagonal columnar and/or smectic phases [97,98]. These properties have already been observed in other organic polymers such as cellulose and aromatic polymers. 

The range of polymers which were found to be able to form liquid crystalhne systems has been considerably extended. Poly(Y-benzyl-L-glutamate) and its analogs, as well as para-aromatic polyamides, exhibit this property in solutions, which served the basis for relating them to lyotropic liquid crystals (see Sect. 2.1). Subsequently, the classes of polymers were found which exhibited such a transition during a change of temperature thermotropic liquid crystals). 

By far the largest group of liquid crystalline polymers containing imide groups are copoly(esterimide)s (PEIs). These have been sub-divided into flexible copolymers containing aliphatic spacers and wholly aromatic copolymers. There are several reports of copoly(amide-imide)s and copoly(ether-imide)s (both thermotropic and lyotropic) and these are treated separately. There are only a few examples of wholly aromatic imide containing LCPs, as polyimides frequently melt well above their decomposition temperature. Successful attempts have been made to incorporate flexible spacers, but in most instances the spacers are based on ether units, and the polymer is more strictly classified as a poly(etherimide). 

A typical example of a thermotropic liquid crystalline polymers is the polyesters and the mesogen substituted polysiloxane. The aromatic amide, the super strength fiber known commercially as Kevlar belongs to the lyotropic liquid crystalline polymers. The other important lyotropic liquid crystalline polymers are poly(7-benzyl-L-glutamate), abbreviated as PBLG, cellulose derivatives, the tobacco mosaic virus, etc. 

Aromatic polyesters undoubtedly represent the most important class of thermotropic nematics. Fully aromatic rod-hke homopolymers such as poly(p-oxybenzoate) or poly (p-phenylene terephthalate) melt at temperatures which are too high to form a stable nematic mesophase. However if the regular chemical structure of the homopolymer is disrupted, the melting temperature is reduced and it is possible to obtain thermotropic nematics. ... 

Novel organometallic poly(arylene)s with 1,3-type (cyclobutadiene)cobalt moieties 27 in the main chain are prepared by Ni(0)-mediated dehalogenative polycondensation of monomers having (cyclobutadiene)cobalt moieties [51], The polymers with of 20 kDa exhibit thermotropic liquid crystallinity. The synthesis of a variety of homometallic and heterometallic oligomers and polymers such as 28 is possible via nucleophilic aromatic substitution reactions of dichlorophenylene-Fe Cp and dihydroxyphenylene-Ru Cp complexes in DMF in the presence of K2CO3 [52]. 

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