Reduced Temperature Curing of Acetylenic Polyimides

Abstract

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 that the products obtained from these reactions are structurally different from 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 benzothiophene linkages. On further heating these polymers can be converted to lightly crosslinked, tough, thermally stable materials with general properties similar to those of the NASA PETI series, and suitable for matrix resins in high-temperature composites, but differing significantly in processing characteristics.