Polyimide foams and their production

Described are flexible polyimide foams having enhanced compression characteristics and softness for use in the manufacture of seat cushions and methods for the production of such foams and precursors therefor. These foams are produced from novel polyimides prepared by reaction of at least one aromatic or heterocyclic primary diamine with a mixture of at least two organic tetracarboxylic acids or derivatives thereof, at least one of which is from 1 to 40 mol percent of a 2-(vicinal-dicarboxycyclohexenyl)succinic acid or derivative thereof and a second of which is an aromatic tetracarboxylic acid or derivative thereof. Foams can be produced having (a) a fatigue life as determined by ASTM test procedure D 3574-81 on foam specimens in the range of from three to five inches in thickness of at least 14,000 cycles, or (b) a compression set as determined by ASTM test procedure D 3574-81, using foam specimens one inch thick and two inches in width and in length, of less than 30% at 50% compression, or both of (a) and (b).