Polyethylene terephthalate (PET) was alcoholised with ethylene glycol to synthesize hydroxytelechelic oligomers of PET. On the other hand, commercial hydroxytelechelic polyepsilon-caprolactone was modified in order to synthesize carboxytelechelic polyepsilon-caprolactone. The chemical structure of the products was investigated by H-1 NMR. Multiblock copolyesters were then synthesized by polyesterification of hydroxytelechelic PET and carboxytelechelic polyepsilon-caprolactone oligomers, using several catalysts and different reaction conditions, which have been linked with the average molecular weight of the obtained block copolyesters. It appeared that residual distannoxane species coming from glycolysis step are best catalyst for polyesterification reaction. The chemical structure of the synthesized copolyesters was investigated by size exclusion chromatography and H-1 NMR. The thermal and thermomechanical behavior of the synthesized copolyesters was investigated by differential scanning calorimetry and by dynamic mechanical analyses. The ester-ester interchange reaction between the two types of oligopolyesters has been enlightened and estimated taking in account the different reaction parameters. This side reaction led to the miscibility of the two phases of the oligomers, that can be explained by a random structure of the copolyester, and prevented to obtain multiblock copolymer. (C) 2003 Elsevier Science Ltd. All rights reserved.