Poly(ether ester) block copolymers were prepared using a transesterification/polycondensation bulk synthesis with systematic control of the terephthalic acid/butanediol aromatic diester block (’hard segment’) and with poly(tetramethylene oxide) [PTMO], poly(hexamethylene oxide) [PHMO], or poly(decamethylene oxide) [PDMO] poly(alkylene oxide) soft segments. The respective number average molecular weights were 980, 930, and 940 Da. A series of the poly( ether ester)s with hard segment fractions of 25, 29, 37, and 51% were prepared. One example of the PDMO polyester was prepared at a 51% hard segment fraction. The polyesters were characterized using viscometry, gel permeation chromatography, H-1-NMR spectroscopy, differential scanning calorimetry, and tensile testing. The novel poly(ether ester)s, the PTMO polyester, and the commercial control, Hytrel(R) 4056, were compared for their resistance to degradation in a 50% aqueous hydrogen peroxide solution at 37 degrees C, boiling water buffered at pH I and 13, an oxygen stream at 200 degrees C, and a nitrogen stream at 200 degrees C. The Hytrel(R) 4056 and the PTMO polyesters fragmented in hydrogen peroxide within 24 h while the PHMO and PDMO polyesters were much less degraded. Resistance to hydrolytic and thermal degradation increased as the ratio of aliphatic methylene to ether increased : PTMO < PHMO < PDMO. Samples containing higher hard segment fractions demonstrated improved resistance to hydrolysis.