Synthesis and thermal characteristics of bisimides. I

Abstract Ten structurally different bisimide resins were prepared by reacting maleic anhydride/citraconic anhydride and benzophenone tetracarboxylic dianhydride with aromatic diamines and fused aromatic structures or heterocyclic groups. The amines included were 1,5‐diaminonaphthalene, 2,5‐bis( p ‐aminophenyl)1,3,4‐oxadiazole, 3,3‐bis( p ‐aminophenyl)phthalide, 9,9‐bis( p ‐aminophenyl)fluorene. and 10,10‐bis( p ‐aminophenyl)anthrone. These monomers were characterized by infrared (IR). 1 H‐NMR, mass spectroscopy, and elemental analysis. Thermal polymerization of these monomers was investigated by differential scanning calorimetry. Broad exothermic peaks were observed for a temperature range of 225–380°C. Temperature of exothermic peak position was influenced by the presence of substituents at the olefinic bond, and in biscitraconimides it was 40–50°C lower than in the corresponding bismaleimides. Anaerobic char yields of cured bisimide resins ranged from 44 to 64%. Oxadiazole‐containing bisimides had low thermal stability. Increase in formula weight between the imide groups did not influence the char yields in a systematic manner. Graphite cloth laminates with two of these bisimide resins were fabricated and tested for a number of physical properties. Their limiting oxygen index was 70–72%.