Reactive compatibilization was used to control and stabilize 20-30 wt% poly(dimethylsiloxane) (PDMS) dispersions in nylon 6 (PA6) and poly(styrene) (PS), respectively. The effect of the type of reaction (amine (NH2)/anhydride (An), NH2/epoxy (E) and carboxylic acid (COOH)/E) on the morphology was studied with electron microscopy. PS and PDMS have mutual solvents and thus it was possible to use gel permeation chromatography (GPC) to determine the concentration of block copolymer in PS/PDMS blends. Reactive blending of PA6 with difunctional PDMS-(An)(2) did not decrease the PDMS particle size compared to the non-reactive blend (similar to 10 mum). Particle size decreased significantly to about 0.5 mum when PA6 was blended with a PDMS containing about 4 random An groups along the chain. For the PS/PDMS blends, GPC revealed that the NH2/An reaction formed about 3% block copolymer and produced stable PDMS particles similar to 0.4 mum. No reaction was detected for the PS-NH2/PDMS-E blend and the morphology was coarse and unstable. Also, PS-NH2/PDMS-An reactivity was lower compared to other systems such as PS/poly(isoprene) and PS/poly(methylmethacrylate) using the same reaction. This was attributed to the relatively thinner PS/PDMS interface due to the high PS/PDMS immiscibility.