The Effects of Polyamic Acid on Curing Behavior, Thermal Stability, and Mechanical Properties of Epoxy/DDS System

A thermoplastic modification method was studied for the purpose of improving the toughness and heat resistance and decreasing the curing temperature of the cured epoxy/4, 4'-diaminodiphenyl sulfone resin system. A polyimide precursor-polyamic acid (PAA) was used as the modifier which can react with epoxy. The effects of PAA on curing temperature, thermal stability and mechanical properties were investigated. The initial curing temperature (T-i) of the resin with 5 wt % PAA decreased about 50 degrees C. The onset temperature of thermal decomposition and 10 wt %-weight-loss temperature for the resin system containing 2 wt % PAA increased about 60 degrees C and 15 degrees C respectively. Besides, the value of impact toughness and plain strain fracture toughness for the modified epoxy resin increased similar to 190% and 55%, respectively. Those changes were attributed to the outstanding thermal and mechanical properties of polyimide, and more importantly to formation of semi-interpenetrating polymer networks composed by the epoxy network and linear PAA. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 3213-3220, 2013