The effect of block copolymer architecture on the suppression of droplet coalescence and on the interfacial elasticity was studied in immiscible blends of polydimethylsiloxane (PDMS) and polyisoprene (PI) with a droplet-matrix morphology. The PDMS-PI diblock copolymers used in this study to compatibilize the blends differ in molecular weight and degree of asymmetry of the blocks. The general Palierne model with an interfacial shear modulus was used to analyze the dynamic measurements performed after different shear histories. It was shown that the coalescence suppression is more effective when the amount of compatibilizer increases and when the overall molecular weight of the block copolymer increases. When comparing the coalescence behavior of a blend and the inverse blend, it was shown that coalescence is suppressed more when the longest block of the block copolymer is located in the matrix. The interfacial relaxation time increases with molecular weight of the blocks for symmetric block copolymers. Asymmetry of the blocks also causes it to increase. A scaling relation is proposed for the interfacial relaxation time of PI/PDMS blends. This master curve is extended for varying viscosity ratios of the blend and with data of a polydimethylsiloxane (PDMS)/polyisobutylene (PIB) blend and a polymethylmethacrylate (PMMA)/polystyrene (PS) blend. (C) 2005 The Society of Rheology.