A series of poly(trimethylene terephthalate)-b-poly(tetramethylene glycol) (PTT-PTMEG) copolymers were synthesized by two-step melt-polycondensation. The copolymers were characterized by using Fourier transform infrared spectroscopy (FTIR), 1H NMR spectroscopy, rheometer, differential scanning calorimetry (DSC), polarized optical microscopy (POM), thermal gravimetric analysis (TGA), and mechanical properties. The results suggest that by increasing the flexible PTMEG contents from 0% to 60？wt%, the copolymers show decreased glass transition temperatures, melting points, melt-crystallization temperatures, hardness, tensile strength, thermostability, and smaller spherulites dimensions; however it has much increased impact strength and elongation at breaking point. Compared with commercial poly(butylene terephthalate) (PBT)-type TPEE with 25？mol% flexible segments, PTT-type TPEE having 25？mol% flexible segments has a lower glass transition temperature, melting point, crystallization temperature, and much lower tensile strength although it has a much higher impact strength than that of PBT-type TPEE, and it is not suitably used as a commercial TPEE. 1. Introduction Thermoplastic polyester elastomers (TPEEs) are linear block copolymers which contain rigid polyester segments and soft polyether segments [1]. In TPEE, both polyether segments and uncrystallized polyester form amorphous phase, while some of the rigid polyester segments form crystals that play the role of physical cross-linking points; thus, TPEEs possess both the elasticity of the rubber and good processability of the thermoplastics. By varying the content of flexible and rigid segments along the chains, the mechanical properties can be adjusted to meet the requirements. Therefore, intensive studies have been carried out on this kind of polymer material. Poly(butylene terephthalate) (PBT) is an industrially used rigid segment in TPEE, and this PBT-type TPEE shows excellent mechanical properties [1]. Polyglycol ether was first introduced to poly(ethylene terephthalate) molecular chains by Du Pont Company, which had better hydrophilicity thus improving the dye ability of products (Hytrel). Multiple TPEE products were developed successively by Toyobo company (Pelprene), GE company (Lomed), Hoechst Celanese company (Retiflex), DSM company (Arnitel), and Elana company (Elitel), and they have been widely used in many fields such as auto manufactory, cable wire, electronic appliances, industrial products, and sports goods [2]. Witsiepe synthesized a poly(ether-ester) by the transesterification and
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