Polyquinoxalines

Polyquinoxalines (PQ) have proven to be one of the better heat-resistant polymers with regard to both stabiUty and potential appHcation. The aromatic backbones are derived from the condensation of a tetramine with a bis-glyoxal, reactions first done in 1964 (61,62). In 1967, a soluble, phenylated version of this polymer was produced (63). The chemistry and technology of polyquinoxalines has been reviewed (64). 

Polyphenylquinoxalines (PPQ) are easier to make than the polyquinoxalines and offer superior solubiHty, processibiHty, and thermooxidative stabiHty (65). The PPQs exhibit excellent high temperature adhesive, composite, and film properties. However, to increase the use temperature of PPQs, acetylene... 

Polyquinoxalines are prepared by the solution polymerisation of aromatic bis((9-diamines) such as 3,3, 4,4 -tetraminobiphenyl and aromatic bis(glyoxal hydrates) such as 4,4 -oxybis(phenylglyoxalhydrate) ... 

Polyquinoxalines Stable in air at 500°C (932°F) tough, somewhat flexible resins make film, adhesive. 

The synthesis of polyether quinoxaline by nucleophilic displacement discussed in Section 5.4.2.2 has also been used for the preparation of hyperbranched polyquinoxaline based on AB2 or A2B monomers. In the AB2 monomer the focal point is a single fluoro group (Fig. 5.42)172 in the A2B the focal point is a single... 

Figure 5.41 Polyquinoxaline syntheses by catalyzed dehalogenative polycondensation.

Poly(phenylenethylene), dendronized, 522 Poly(phenylenevinylene) optically active, 510-511 synthesis of, 495-496 Poly(/ ara-phenylenevinylene)s, 472 Polypheny lquinoxaline (PPQ) hyperbranched, 312-314 synthesis of, 309-313 Polyphosphoric acid, 333 Polypropylene oxide) polyol, 223 Polypropylene polyols, 220 Poly (pyridine), synthesis of, 503-505 Polyquinoxaline (PQ), synthesis of, 309-313... 

T. Yamamoto, K. Sugiyama, T. Kushida, T. Inoue, and T. Kanbara, Preparation of new electron-accepting Tr-conjugated polyquinoxalines. Chemical and electrochemical reduction, electrically conducting properties, and use in light-emitting diodes, J. Am. Chem. Soc., 118 3930-3937, 1996. 

Polyquinoxalines, ladder structured conducting, 7 522 Polyrotaxane structures, 23 733 Polysaccharide extraction, 10 307... 

Certain polyquinoxalines are thermo-stable with high glass transition temperatures up to 435°C,high decomposition temperatures (510-560°C) and notable oxidative resistance in air, but, on the other hand, they form highly viscous solutions that don t wet reinforcing fibres easily. 

Polymers such as PBI have a weak link in them since a single covalent bond connects the phenyl rings in biphenyl. This weakness is overcome by the synthesis of ladder polymers, such as polyquinoxaline structures 4.64 and 4.65, and polydithione (structure 4.66), which have two covalent bonds throughout the chain. Thus, the integrity of the polymer is maintained even if one bond is broken ... 

A number of thermally stable polymers have been synthesized, but in general the types of structures that impart thermal resistance also result in poor processing characteristics. Attempts to overcome this problem have largely been concentrated on the incorporation of flexible groups into the backbone or the attachment of stable pendent groups. Among the class of polymers claimed to be thermally stable only a few have achieved technological importance, some of which are polyamides, polyimides, polyquinoxalines, poly quinolines, and polybenzimidazoles. Of these, polyimides have been the most widely explored. 

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