Structure-property relationships in addition polyimides .2. Resins from three-ring aromatic diamines containing carbonyl and methylene groups

The use of flexibilized three-ring aromatic diamine moieties was investigated in an effort to improve the processing characteristics of addition-type polyimide resins. A series of 10 diamines containing carbonyl and methylene bridging groups was synthesized. The diamines were polymerized with the dimethylester of 3,3',4,4'-benzophenonetetracarboxylic acid (BTDE), using the monomethyl ester of nadic acid (NE) as an endcap. The effect of diamine structure on the solubility and rheological properties during cure was determined. The effect of diamine structure and formulated molecular weight on the thermo-oxidative stability and glass transition temperature of the polyimides was also investigated. Unidirectional laminates were fabricated from selected resins, using carbon fibre as the reinforcement. Interlaminar shear strength and flexural properties of the laminates were determined. The results indicate that polyimides from some of the diamines containing methylene bridging groups have potential as matrix resins for long-term applications at temperatures up to 300 degrees C.