Polyphenylenes, aromatic heterocyclic

PHENYLATED AROMATIC HETEROCYCLIC POLYPHENYLENES CONTAINING PENDANT DIPHENYLETHER AND DIPHENYLSULFIDE GROUPS... 

Watt and Drummond, were considered to be inert for C-C bond forming reactions. However, by the expedient of transmetallation to Cu, Ni, Zn, Li, and Al, methodologies for the stereoselective synthesis of olefins and dienes, as well as unusual heterocycles, aromatics and their ring-annulated products are now available which are beginning to make impact on material science, e. g. synthesis of pentacenes and polyphenylenes. Takahashi and Li provide evidence that, with further developments in transmetallation and handling the zirconacycles outside of the Schlenk tube techniques, synthetic utility will increase and new catalytic reactions will be developed. 

In the Phillips process, polyphenylene sulfide (PPS) is obtained from the polymerization mixture in the form of a fine white powder, which, after purification, is designated Ryton V PPS. Characterization of this polymer is complicated by its extreme insolubility in most solvents. At elevated temperatures, however, Ryton V PPS is soluble to a limited extent in some aromatic and chlorinated aromatic solvents and in certain heterocyclic compounds. The inherent viscosity, measured at 206°C in 1-chloronaphthalene, is generally 0.16, indicating only moderate molecular weight. The polymer is highly crystalline, as shown by x-ray diffraction studies (9). The crystalline melting point determined by differential thermal analysis is about 285°C. 

Cold wall heats of ablation values ranged between 7700 and 13,800 Btu/lb. The best performance was obtained with the heterocyclic polyimide and polybenzimidazole and the aromatic polyphenylene resins, all of which exceed the heat of ablation for the widely used phenol formaldehyde (phenolic) resin. The superior charring characteristics of these polymers contributed greatly to their high heats of ablation. The various plastic materials, with their inherently low thermal conductivities, greatly restricted the flow of heat from the surface region into the specimen substrate. 

High thermal stability can be achieved by making full use of resonance energy and resonance stabilization of aromatic and heterocyclic structures such as in polyphenylene and polyphenylquinoxalines. 

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