The reaction product of both methylbenzoate and dimethylphthalate with dibutyltin oxide was determined to be an 1-alkoxy-3-acyloxy distannoxane by multinuclear n.m.r. spectroscopy (H-1, C-13 and Sn-119) in solution. Dibutyltin oxide promotes ester interchange reactions. It was used to compatibilize the immiscible blend of polyethylene terephthalate glycol (PETG) with the ethylene vinyl acetate (EVA) copolymer. The linear viscoelastic properties of the compatibilized blend were determined and analysed in light of the n.m.r. results.