Polyphenyls thermal stability

Since the thermal degradation in phenylated polyphenyls of the type XXa is caused by the loss of pendant phenyl groups, and since the reported (4, 7, 9, 10, 11, 14, 15) properties of p-polyphenylenes are quite different from those of XXa, the synthesis of an unphenylated polyphenylene by this pathway was of considerable significance. Only a few results employing this reaction have thus far been obtained. [The p-poly-phenylenes reported are black or brown, insoluble, crystalline materials of lower thermal stability than XXa.]... 

The polymerization of the bispyrones XXX and XXXI with p-diethynyl-benzene (XVIII) in toluene at 225°-300°C. for 20-48 hours produced both soluble and insoluble fractions of polymers XXXII and XXXIII (Reactions 21 and 22). The soluble portions were only relatively low molecular weight ( [17] = 0.1). These materials did show the same excellent thermal stability as exhibited by the polyphenyls of type XIX and XX. 

Table 17-3 shows thermal stability data obtained by Brown, Aftergut and Blackington [10] for three classes of aromatic compounds unsubstituted polyphenyl hydrocarbons, polyphenyl ethers, and silanes sub-... 

The literature contains fragmentary information on the thermal stability of certain liquid polyorganosiloxanes it is indicated that poly-dimethylsiloxane liquids are stable up to 175°C [6], while polyphenyl-... 

Polypheny I Ethers. Both alkyl-substituted and iinsubxtiinlcd polypheny ethers are included in this class of synthetic lubricants. General preparation involves the (.llhiian ether synthesis. The unsubstituted polyphenyl ethers have outstanding thermal, oxidative and radiation resistance, however, poor low-temperature characteristics arc a major drawback. Alkyl substitution improves low-temperature viscosity, but detracts from stability. Most lubricant uses are developmental in nature and involve aircrali and aerospace applications. 

The stability of organic (and other covalent) compounds to radiation is frequently expressed by means of the "G" value, which is equal to the number of molecules decomposed, or of product formed, per 100 eV of energy dissipated in the material. As an example of the use of G values, the data in Table 3 are for a number of polyphenyls exposed to the radiation in a thermal reactor. 

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