Reduced temperature curing of acetylenic polyimides

The onset temperature for the curing reactions of phenylethynyl-terminated oligomers can be lowered by the addition of disulfides which dissociate to form thiyl radicals on heating. Studies using model compounds have shown th at the products obtained from these reactions are structurally different fr om those obtained in the absence of the additives. The low-temperature cure reactions of oligomers containing aromatic disulfides as backbone moieties initially yield high molecular weight thermoplastic polymers containing be nzothiophene linkages. On further heating these polymers can be converted t o lightly crosslinked, tough, thermally stable materials with general prope rties similar to those of the NASA PETI series, and suitable for matrix res ins in high-temperature composites, but differing significantly in processi ng characteristics.