Thermoset polyimide matrix resins with improved toughness and high Tg for high temperature carbon fiber composites

Thermoset polyimide matrix resins with high melt processability for high-temperature carbon fiber composites were prepared from the diethyl ester of 3,3′,4,4′-benzophenonetetracarboxylic acid (BTDE) and the aromatic diamine mixtures consisting of 4,4′-bis(4-amino-2-trifluoromethylphenoxy)biphenyl (6FBAB) and p-phenylenediamine (p-PDA) with the monoethyl ester of 5-norbornene-2,3-dicarboxylic acid (NE) as the molecular-weight-controlling and reactive endcapping agent. The effects of diamine mixture compositions on the melt processability of the B-staged oligoimides and the thermal and mechanical properties of the thermally cured polyimide resins were systematically investigated. Experimental results indicated that the polyimide matrix resins with p-PDA concentration of ≤ 40% in 6FBAB + p-PDA showed lower melt viscosities, corresponding to a higher melt processability, than the conventional thermoset polyimide (PMR-15). After thermal curing, the thermoset polyimides exhibited a very good combination of thermal and mechanical properties with the glass transition temperature (Tg) of as high as 353 °C determined by differential scanning calorimetry and impact strength of 15.2 kJ m−2. Carbon fiber-reinforced composite derived from the representative polyimide resin showed good mechanical properties at temperatures of as high as 288 °C.