Fluorinated PMR polyimides with improved melt processability and impact toughness

Fluorinated in situ polymerization of monomeric reactants (PMR) polyimide resins with improved melt processability and impact toughness were prepared from the diethyl ester of 3,3 ' ,4,4 ' -benzophenonetetracarboxylic acid and the aromatic diamine 4,4 ' -bis(4-amino-2-trifluoromethylphenoxy)biphenyl (6FBAB) with the monoethyl ester of 5-norbornene-2, 3-dicarboxylic acid as the molecular-weight-controlling and reactive endcapping agent. Effects of the calculated molecular weights (calc’d M n values) on the resin melt processability and the thermal and mechanical properties of the thermally cured polyimides were systematically investigated. It was found that the fluorinated PMR resins with calc’d M n of ≤ 2500 g mol -1 exhibited higher melt processability than the conventional PMR-15. After thermally cured, the thermoset polyimides displayed high thermal stability with the decomposition temperature at 5% weight loss ( T 5 ) of > 62; 450 ° C, the glass transition temperature ( T g ) of 273—326 ° C, and good mechanical properties. Carbon-fiber-reinforced composites fabricated from the representative polyimide showed outstanding mechanical properties both at ambient and elevated temperatures as well as high impact toughness at room temperature.