Bisphenol-A polycarbonate (BAPC) is an important engineering plastic with superior optical and mechanical properties, but it is difficult to be processed due to the high melt viscosity. In this work, the blends of BAPC and reactive plasticizer of diallyl phthalate (DAP) were studied before and after polymerization of DAP using dicumyl peroxide (DCP) as thermal initiator. The morphology evolution and phase transitions of the blends during heating were investigated by polarized optical microscopy equipped with hot stage and differential scanning calorimetry. With raising temperature, the apparent phase transitions, i.e., thermally induced partial phase separation with upper critical solution temperature (UCST) behavior, BAPC cold crystallization, DAP polymerization and BAPC crystal melting, occurred in sequence. Compared to pure BAPC, the BAPC/poly(DAP) blends with 10-15 wt.% of poly(DAP) had good performances, including similar glass transition temperature, tensile strength and similar to 80% of optical transmittance in the wavelength range of 600-800 nm, as well as an increase of 64-68% for moduli and 100-135% for melt flow index, respectively. These good performances were attributed to the bicontinuous structure of the blends. This study provides a facile strategy to realize the easy processing for intractable polymers and to maintain, even to enhance the high performances of the original polymers. (C) 2016 Elsevier Ltd. All rights reserved.