Certain styrene/maleic anhydride copolymers (SMA) are completely miscible with poly(methyl methacrylate) (PMMA). This paper explores the solubilization of SMA copolymers in the grafted PMMA shell layer of emulsion-made core-shell impact modifiers by examining glass transition behaviour and morphology of SMA/core-shell modifier blends. There appears to be a single, composition-dependent hard phase T-g for these blends at all compositions by dynamic mechanical analysis. Transmission electron microscopy reveals that SMA copolymers are evenly distributed around the core-shell particles. Neither approach was able to determine the upper solubilization limit expected from theoretical considerations. A blend of core-shell modifier with polystyrene (PS), which is not miscible with PMMA, was also examined for comparison.