CROSS-LINKED POLYIMIDES WITH PYROMELLITIM IDE FRAGMENTS BETWEEN CROSS-LINKS

Cross-linked polyimides were synthesized on the basis of bismaleimide with pyromellitimide fragments between cross-links, The role of amic a cid fragments in the reactions of copolymerization and polymerization at the double bonds of the maleimide cycle, determining the structure of copolymers, was studied, It was shown that the presence of these fr agments in the reaction mixture reduces to 80-120 degrees C the temper ature of interaction between terminal amino groups and the double bond s of the maleimide cycle, The decrease in the onset temperature of the copolymerization reaction allows the molecular mass of the fragments between cross-links, formed at temperatures below 150 degrees C. The f ormation of additional imide cycles and a higher conversion of the dou ble bonds at temperatures above 150 degrees C markedly increase the th ermal stability of cross-linked polymers.