A series of aliphatic poly(ether-ester)s based on flexible poly(tetramethylene oxide) (PTMO) and hard poly (butylene succinate) (PBS) segments were synthesized by the catalyzed two-step transesterification reaction of dimethyl succinate, 1,4-butanediol, and alpha,omega-hydroxy-terminated PTMO (M-n = 1000 g/mol) in the bulk. The content of soft PTMO segments in the polymer chains was varied from 10 to 50 mass %. The effect of the introduction of the soft segments on the structure, thermal, and physical properties, as well as on the biodegradation properties was investigated. The composition and structure of the aliphatic segmented copolyesters were determined by H-1 NMR spectroscopy. The molecular weights of the polyesters were verified by viscometry of dilute solutions and polymer melts. The thermal properties were investigated using DSC. The degree of crystallinity was determined by means of DSC and WAXS. Biodegradation of the synthesized copolyesters, estimated in enzymatic degradation tests on polymer films in phosphate buffer solution with Candida rugosa lipase at 37 degrees C, was compared with hydrolytic degradation in the buffer solution. Viscosity measurements confirmed that there was no change in molecular weight of the copolyesters leading to the conclusion that the degradation mechanism of poly(ester-ether)s based on PTMO segments occurs through the surface erosion. (c) 2007 Wiley Periodicals, Inc.