NEW SEMI-INTERPENETRATING POLYMERIC NETWORKS FROM LINEAR POLYIMIDES AND THERMOSETTING BISMALEIMIDES .2. MECHANICAL AND THERMAL-PROPERTIES OF THE BLENDS

Two linear polyimides, BAPPY-BTDA and BAPB-BTDA, prepared by condensation of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) with 3,3′-[2,6-pyridinediylbis(oxy)]bisbenzene amine (BAPPY) and 3,3′-[1,3-phenylenebis(oxy)]bisbenzene amine (BAPB), and three thermosetting bismaleimides (BMI), PPY-BMI, PB-BMI and MDA-BMI, synthesized from the two preceding aromatic diamines and 4,4′-methylenebis(1,4-phenylene) (MDA), were blended to obtain the following mixtures: BAPPY-BTDA/PPY-BMI, BAPPY-BTDA/MDA-BMI and BAPB-BTDA/PB-BMI. These three types of mixture were cured up to 300°C to give semi-interpenetrating polymeric networks (IPNs). Thermomechanical and dynamic mechanical analysis of semi-2-IPN films essentially pointed out a phase separation between the linear polyimide and the crosslinked bismaleimide with probably partial miscibility between the polyimide and oligomeric or unreacted bismaleimide compounds. Thermogravimetric analysis showed that the thermal resistance of semi-IPNs was dramatically decreased as the bismaleimide concentration increased. Compared to the free linear polyimides, the semi-interpenetrated structure led to a reduction of the room-temperature adhesive joint strengths but allowed the conservation of adhesive and mechanical tensile properties in the region of the glass transition temperature of the linear polyimide. © 1990.