Polymer materials with improved properties can be obtained through polymer blends. As a polymer mixture is generally immiscible and incompatible, it is necessary to develop new methods to improve the interfacial adhesion. The aim of this work is to find formulations and associated processes to upgrade engineering polystyrene (PS) and polycarbonate (PC) polymer blends with the objective of using the best process-formulation couple. In this study, blends of PS/PC were prepared in molten medium using reactive extrusion after UV-irradiation. The effects of UV-irradiation on some properties of blends under molten medium were investigated by differential scanning calorimetry (DSC), fourier transform infrared (FTIR), and thermogravimetric analysis (TGA). The data showed that the presence of polycarbonate in the blend increased the tensile strength and elongation at break with respect to pure PS. The mechanical properties of the blends were improved after irradiation. All irradiated blends are thermally more stable than those nonirradiated. Chemical changes can be clearly seen in FTIR spectra through two bands assigned to C=O and OH groups. The mutual influence between the PS/PC polymer blends compositions during UV-irradiation was studied. PS and PC have different photo-mechanisms due to the larger UV absorption of polystyrene and formation of more stable tertiary carbon radicals. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012