α-(3-Aminopropyl-l-amino)polystyrene (α-amino-PS) was melt-blended with styrene/maleic anhydride copolymers (SMA) containing 28 wt% maleic anhydride groups. The terminal primary amino group can react with the maleic anhydride monomer units in SMA, forming imides. The resulting product turned out to be an efficient emulsifier for SMA blends with poly(phenylene oxide) (PPO). At constant weight fraction of added α-amino-PS, the size of the dispersed PPO particles decreased with decreasing molar mass, i.e. increasing mole fraction, of the α-amino-PS. In a second series of experiments, α-amino-PS with Mn>Mentanglement, was used to compatibilize SMA/PPO blends which also contained poly(acrylonitrile-co-butadiene-co-styrene) and some poly[styrene-b-(ethylene-co-butylene)-b-styrene] triblock copolymer. Although, in this case, it was not possible to detect major changes in the phase texture or morphology, it could be shown that the addition of α-amino-PS improved the impact strength significantly. For comparison, blends were also prepared with unmodified PS of a similar . No corresponding improvement of the mechanical properties was observed in this case.