Thermal aging of block copolymers of bisphenol A polycarbonate and polydimethylsiloxane (BPAPC and PDMS) have been studied. Changes in notched izod impact performance and yield stress are reported following aging at 120 degrees C and 130 degrees C for up to 20 days. Retention of impact at 120 degrees C of the block copolymers was found to improve with increasing size of siloxane domains in the polycarbonate matrix. Quite contrary to our expectation, the retention of impact for a given sample at 130 degrees C was found to be better than that of at 120 degrees C. These block copolymers showed (thermo) reversible ductility rejuvenation behavior at 130 degrees C when the samples heat-aged at 120 degrees C were shifted from 120 to 130 degrees C. Transmission electron microscopy, small-angle X-ray scattering, and dynamic mechanical analysis techniques were used to probe the observed phenomenon. POLYM. ENG. SCI., 49:1719-1726, 2009. (C) 2009 Society of Plastics Engineers