Networks Crosslinked by Ethynyl End-Caps and Pendant Groups

3 Networks Crosslinked by Ethynyl End-Caps and Pendant Groups 

For the most demanding conditions poly(phenylquinoxaline) and polyimide oligomers were created, some end-capped only and others containing ethynyl pendant groups. Typical of the end-capped polyfphenylquinoxalines) are [597, 598]  

In attempts to improve the processibility of the poly(phenylquinoxaline) oligomers, some were altered by changing the bridging moieties between phenyl rings and introducing more flexible groups into the chain [598-600]  

Polyfphenylquinoxaline) oligomers containing pendant ethynyl groups were prepared, in which the ethynyls are either hindered [601] or not [602], and their number per oligomer molecule may be altered to best fit the desired processing 

Despite all the synthetic and processing efforts, composite materials containing poly(phenylquinoxaline) network matrices remain in very limited use. This is due to several reasons. Among them, one can enumerate the costs of monomers and of synthesis, lower than expected thermooxidative stability [598], reduced demand from the defense industry and, most important, the suspect carcinogenicity of the pivotal monomer 3,3 -diaminobenzidine [597]. The verified or suspect carcinogenicity of essentially all aromatic ortho-diamines makes it highly unlikely for poly(phenylquinoline) polymers and reactive oligomers to be in broad use in the future unless a new synthetic route to quinoxalines is found in which aromatic ortho-diamines are not used. 

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