POLYIMIDE-MODIFIED EPOXY SYSTEM - TIME-TEMPERATURE TRANSFORMATION DIAGRAMS, MECHANICAL AND THERMAL-PROPERTIES

A hot-melt processable thermoset was prepared by blending diaminodiphe nylmethane/4,4'-diaminodiphenylsulfone epoxy resin and a high-T(g) the rmoplastic polyimide. The polyimide was synthesized from 3,3',4,4'-ben zophenonetetracarboxylic dianhydride and 4,4'-(9H-fluoren-9-ylidene)bi sphenylamine to form a linear structure initially miscible with the ne at epoxy resin. The thermal polymerization study, including determinat ion of time-temperature-transformation cure diagrams, pointed out a lo wering in crosslink density of epoxy network probably due to the polyi mide viscosity effect. After cure, no phase separation could be observ ed by scanning electron microscopy and only one T(g) was detected by d ynamic mechanical analysis, showing full miscibility between the blend components. The consequences of the thermoplastic incorporation (poly imide concentration=10wt%) were a slight increase in T(g) value (DELTA T(g)=+ 5-degrees-C) and rather limited improvements in stress at ruptu re (50%) and strain-energy release rate G(Ic) (27%) compared to the un modified epoxy matrix.