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ABSTRACT:Polymer blends based on various ratios of polystyrene (PS) and polymethyl methacrylate (PMMA) were exposed to different doses of gamma radiation up to 25 Mrad. The structure-property behavior of the polymer blends before and after they had been irradiated was investigated by DSC, TGA, and FTIR spectroscopy. The DSC scans of the glass transition temperature (T g ) of the different polymer blends showed that the T g was greatly decreased by increasing the ratio of the PMMA component in the polymer blends. Moreover, the T g of PS/PMMA blends was found to decrease with increasing irradiation dose. The depression in T g was noticeable in the case of blends rich in PMMA component. The TGA thermograms showed that the thermal stability of the unirradiated polymer blends decreases with increasing the ratios of PMMA component. Also, it was found that the presence of PS polymer in the blends affords protection against gamma radiation degradation and improves their thermal stability. However, exposing the polymer blends to high doses of gamma radiation caused oxidative degradation to PMMA components and decreased the thermal stability. The investigation of the kinetic parameters of the thermal decomposition reaction confirm the results of thermal stability. The FTIR analysis of the gamma-irradiated polymer blend films gives further support to the TGA data.