A reactive blend of poly(ethylene glycol) (PEG) and DL-oligo(lactic acid) (OLA) is obtained at high temperature to produce partial PEG/OLA multiblock copolymer without purification. The reactive blend of PEG and OLA easily reacts with poly(1,4-butylene terephthalate) (PBT) in the melt leading to the formation of highmolar mass poly(1,4-butylene terephthalate-co-ethylene oxide-co-DL-lactide) (PBTEOLA) copolymers. The analysis from 1 H NMR and solubility test reveals that the transesterification between butylene terephthalate (BT), ethyleneoxide (EO), and lactide (LA) segments during synthesis is unavoidable. The copolyesters are segmented copolyesters with certain random properties, as confirmed by their thermal behavior. The copolyesters show only one melting temperature (T m ) on the second heating run and one crys-tallization temperature (T c ) on the cooling cycle from differential scanning calorimetry measurement. With increase of OLA feeding composition in PEG/OLA blend or increase of content of PEG/OLA blend, the T m and T c of copolyesters decrease, and solubility increases. The conventional size-exclusion chromatography polystyrene calibration estimates weight-averaged molecular weight of the copolyester to be as high as 66,600 g/mol. Mechanical tests indicate that the copolyesters exhibit high Young's modulus of 50-100 MPa and good elongation at break of 32-137%.

The copolymers of poly(1,4-butylene terephthalate-co-ethylene oxide-co-DL-lactide), obtained by the transesterification reactions of poly(butylenes terephthalate) with poly(ethylene glycol DL-oligo(lactic acid), were fabricated into porous scaffolds by the established solvent-casting and particulate-leaching technique with NaCl as the porogen. The morphology of the porous scaffolds were investigated by the scanning electron microscopy (SEM), and the pores within the scaffold were proven to be interconnective ranging in size from 200 to 400 μm. The human bone marrow mesenchymal stem cells (MSC) seeded on the scaffolds were confirmed to survive and proliferate within the pores of the scaffold with the observation by immunofluorescence microscope and SEM. In vivo implantation of MSC-seeded scaffolds into athymic nude mice showed significant tissue formation in the subcutaneous sites of the immunodeficient mice at 3, 4, 6, and 9 weeks. The results indicate that the scaffolds were biocompatible with MSC and the host tissue in vitro and in vivo.