The emulsification efficiency of PS-co-TMI, a copolymer polymerized by styrene and 3-isopropenyl-α,α-dimethylbenzene isocyanate (TMI), for polystyrene (PS)/polyamide 6 (PA6) blend was studied. During the mixing process, an effective emulsifier PS-g-PA6 was generated, which was demonstrated by differential scanning calorimetry (DSC) and fourier transform infrared spectroscopy. PS-g-PA6 generated by PS-co-TMI with high TMI content was found to contain some unreacted isocyanate active groups which reduced using efficiency of PS-co-TMI. Irrespective of TMI content in PS-co-TMI, the dosage of PS-co-TMI reached 20 wt %, unreacted PS-co-TMI was detected. These results indicated that reactive emulsification limits for both active groups' content and reactive precursors' dosage. After the rational addition of PS-co-TMI into PS/PA6 system, phase sizes of co-continuous structure were reduced conspicuously. However, co-continuous structure was evolved into matrix-dispersed structure while the dosage of PS-co-TMI reached 20 wt %. Emulsification efficiencies of PS-co-TMI with different TMI contents, 2.2, 4.1, and 7.5 wt %, were compared. The results revealed PS-co-TMI with 2.2 wt % TMI content had the highest reactive emulsification efficiency because of the block-copolymer-inclined emulsifier generated in the mixing process. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 39972.