Block copolyesters containing both polydimethylsiloxane and poly(trimethylene terephthalate) (PTT) blocks were prepared by polycondensation reaction. Although hydroxyl-terminated siloxane oligomer (H-PDMS) and 1,3-propanediol are immiscible, their mixture can form an azeotrope with a low boiling point. It was found that the reactions were preceded at lower temperature, shorter reaction times and lower degree of vacuum than the traditional way. With increasing H-PDMS content, the occurrence time of Weissenberg effect is gradually shortened. The structure and thermal performances of the block copolymers was characterized by using the Fourier transform infrared spectroscopy (FTIR), H-1 NMR, Ubbelohde viscometer, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and polarizing microscopy, respectively. The block copolymers have lower glass transition temperatures, cold-crystallization temperatures, melting points, starting decomposition temperatures but higher maximum decomposition rate temperatures and higher amount of residue than those of pure PIT. The block copolymers with less H-PDMS content have larger storage modulus and loss modulus than those of pure PTT. The copolyester is-easier to form banded spherulites at lower temperatures than that of pure PTT. Microphase separation and aggregation of polydimethylsiloxane blocks occurs in the material that is favorable for improving the impact strength of the material. (C) 2014 Elsevier B.V. All rights reserved.