A novel coupling agent containing 2-oxazoline and 2-oxazinone as well as hydrosilane moieties has been prepared by hydrosilylation of the corresponding allyl ether containing precursor with a methylhydrosiloxane-dimethylsiloxane copolymer. This hydrosiloxane containing coupling agent, termed as SCA, was characterized by H-1 NMR and its crosslinkability was proven by DSC. SCA was used for the modification of the interfaces in heterogeneous polymer blends. In a model blend system based on mono-carboxylic acid terminated polystyrene (PS-COOH) and mono-amino terminated poly(methyl methacrylate) (PMMA-NH2) the 2-oxazoline and 2-oxazinone units of SCA can selectively react with the carboxylic groups or amino groups. respectively. The remaining hydrosilane units partially crosslink under the used mixing conditions. The morphology of the three-component blends prepared by melt mixing was evaluated. SCA is immiscible with the polymers and forms its own phase. The expected location of the SCA at the interface between the polymers was proven only in an annealed, strongly phase separated blend. Overall the effect of the compatibilizer on the morphology is very small. Neither the domain size nor the composition for phase inversion are significantly affected in this blend system by the presence of SCA. (c) 2005 Elsevier Ltd. All rights reserved.