In this study, the structural and morphological properties of poly(methyl methacrylate)/poly(acrylonitrile-g-(ethylene-co-propylene-co-diene-g-styrene) (PMMA-AES) blends were investigated with emphasis on the influence of the in situ polymerization conditions of methyl methacrylate. PMMA-AES blends were obtained by in situ polymerization, varying the solvent (chloroform or toluene) and polymerization conditions: method Ano stirring and air atmosphere; method Bstirring and N2 atmosphere. The blends were characterized by infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and dynamic mechanical analysis (DMA). The results showed that the PMMA-AES blends are immiscible and present complex morphologies. This morphology shows an elastomeric dispersed phase in a glassy matrix, with inclusion of the matrix in the elastomer domains, suggesting core shell or salami morphology. The occlusion of the glassy phase within the elastomeric domains can be due to the formation of graft copolymer and/or phase inversion during polymerization. However, this morphology is affected by the polymerization conditions (stirring and air or N2 atmosphere) and by the solvent used. The selective extraction of the blends' components and infrared spectroscopy showed that crosslinked and/or grafting reactions occur on the elastomer chains during MMA polymerization. The glass transition of the elastomer phase is influenced by morphology, crosslinking, and grafting degree and, therefore, Tg depends on the polymerization conditions. On the other hand, the behavior of Tg of the glassy phase with blend composition suggests miscibility or partial miscibility for the SAN phase of AES and PMMA. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012