Polyphenylquinoxalines: Synthesis, characterization, and mechanical properties

The synthesis of polyphenylquinoxalines (PPQ) is discussed in detail. Solutions of PPQ at 20% solids content from stoichiometric quantities of pure reactants are generally metastable, increasing in viscosity and, in some cases, gelling. This can be alleviated without any appreciable detrimental effect upon the polymer by upsetting the stoichiometry of the reactants. Relatively high molecular weight polymer (η inh = 1.84 dl/g; H 2 SO 4 , 0.5%, 25°C) can be obtained when the stoichiometry is upset by 2%. Several new PPQ are reported which contain multiple phenyl ether groups located in the para position of the substituted phenyl ring. Introduction of a phenoxy group decreased T g by 70°C. The properties of random and block copolymers of phenylquinoxaline and phenyl‐as‐triazine units are reported. Depending upon the processing conditions, PPQ Ti tensile shear specimens gave RT strength of 4900 psi and 316°C strength after 500 hr at 316°C of 1500 psi. Unidirectional high‐modulus graphite composites provided RT flexural strength of 123,000 psi, flexural modulus of 15.6 × 10 6 psi, and inter‐laminar shear strength of 7000 psi.