SYNOPSISMiscibility studies on blends of polycarbonate (PC ) and poly (phenyl methacrylate) (PPMA) were undertaken by means of differential scanning calorimetry (DSC) , dynamic mechanical, and dielectric relaxation methods. PC and PPMA were mixed by dissolving in tetrahydrofuran (THF) and subsequently coprecipitated in methanol. DSC studies showed a single glass transition ( T,) that shifts systematically with composition. These Tgs are reproducible in repeated DSC heating cycles, suggesting true miscibility of the pair.The dry PC and PPMA pellets were melt mixed in a Mini-Max Mixer/Molder. The extrudates were compression molded. These melt-mixed PC/PPMA blends exhibited glasslike transparency and also showed a single Tg in the DSC scans. The true miscibility of PC and PPMA was further confirmed by dynamic mechanical and dielectric relaxation methods. The net birefringence has been reduced substantially because of the opposite sign of the intrinsic birefringence of PC and PPMA molecules. At the 12/88 PC/PPMA, the birefringence remains zero at all draw ratios, indicating the achievement of birefringencefree polymer alloys.