This work examines the effect of the extent of reaction on morphology, continuity development and cocontinuity in highly reactive nanoscale blends of brominated poly(isobutylene-co-p-methylstyrene) (BIMSM) and polyamide (PA) containing different amounts of plasticizer. The reactive melt blending protocol used is shown to be very effective in generating fine droplets in the 50-80 nm range scale, as observed by atomic force microscopy, and producing high amounts (about 46%) of graft copolymer. The amount is even higher (about 57%) for plasticized blends. It can be seen that the reaction between the elastomer and PA shifts the percolation thresholds and overall continuity development in the system to higher concentrations, but no effect is observed on the concentration region of dual-phase continuity. When a plasticizer is added to the PA, and it is the matrix phase, elastomer continuity development and cocontinuity shifts to higher concentrations. This is a result of both the increased extent of reaction in the presence of a plasticizer and the lower viscosity of the PA phase. When plasticized PA is the dispersed phase, however, these two phenomena oppose each other. The increased extent of reaction shifts plasticized PA continuity development to even higher concentrations in the blend, but the lower viscosity of the plasticized PA phase shifts the continuity development to lower PA phase concentrations. The net effect is that no change is observed on PA phase continuity with addition of plasticizer in an elastomer matrix. It is found, overall, that the dominant factor in controlling the dispersion of higher concentrations of elastomer into the PA phase is the extent of reaction between BIMSM and polyamide. (C) 2011 Elsevier Ltd. All rights reserved.