Terminal maleic anhydride functionalized polystyrenes were synthesized using atom transfer radical polymerization (ATRP). The functionality of these polymers was determined through their reaction with poly(ethylene glycol methyl ether) (PEGM) followed by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR). Melt mixing of these reactive polystyrenes with nylon 6 resulted in blends with good mechanical properties attributed to an in situ formation of a copolymer which may be used for the compatibilization of the binary nylon 6/polystyrene. The mechanical properties of the resulting ternary blends were significantly improved with the addition of the modified polystyrene even when the molecular weight of the polystyrene used was higher than that of the respective block in the copolymer. The enhanced mechanical properties, as well as the fine PS dispersion in the nylon 6 matrix revealed by scanning electron microscopy of the compatibilized cryofractured samples, support the hypothesis that an effective compatibilization of nylon 6/PS has been achieved.