Quinoxaline Ladder Polymers for High Temperature Laminating Resins.

N-Phenyl-substituted quinoxaline ladder polymers were synthesized by the condensation polymerization of 2,3,7,8-tetraphenoxy-1,4,6,9-tetraazaanthracene and 2,3,7,8-tetraanilino-1,4,6,9-tetraazaanthracene. It had been postulated that related quinoxaline ladder polymers reached a rigid, unreactive state at low molecular weights partly because of intermolecular hydrogen bonding, and the phenyl substituents were expected to prevent these excessive intermolecular forces. However, these polymers also failed to polymerize to sufficiently high molecular weights to produce a cohesive laminating resin. A method of preparing similar but highly crosslinked resins was investigated. This method consisted of condensing tetraphenoxy-tetraazaanthracene with benzidine to replace some of the phenoxyl substituents and to form a linear or branched prepolymer, followed by displacing the remaining phenoxyl groups with aniline and condensing the resulting prepolymer with more tetraphenoxytetraazaanthracene to form ladder segments in the final cure. A glass fabric-reinforced laminate was molded from this polymer with a flexural strength of 11,400 psi. The prepolymer derived from tetraphenoxytetraazaanthracene and benzidine was also cured directly by heating, although the product was expected to have only very short ladder segments in its highly crosslinked structure. A laminate fabricated from this resin had a flexural strength of 27,200 psi.
See also AD-864 104.