The synthesis of two low molecular weight linear unsaturated oligoester precursors, poly(propylene fumarate-co-sebacate) (PPFS) and poly(ethylene fumarate-co-sebacate) (PEFS), are described. PPFS, PEFS, and poly(ethylene glycol) are then used to prepare poly(propylene fumarate-co-sebacate)-co-poly (ethylene glycol) (PPFS-co-PEG) and poly(ethylene fumarate-co-sebacate)-co-poly(ethylene glycol) (PEES-co-PEG) block copolymers. The products thus obtained are investigated in terms of the molecular weight, composition, structure, thermal properties, and solubility behavior. A number of design parameters including the molecular weights of PPFS, PEFS, and PEG, the reaction time in the polymer synthesis, and the weight ratio of PEG to PPFS or to PEFS are varied to assess their effects on the product yield and properties. The hydrolytic degradation of PPFS-co-PEG and PEES-co-PEG in an isotonic buffer (pH 7.4, 37degreesC) is investigated, and it is found that the fumarate ester bond cleaves faster than does the sebacate ester bond. (C) 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 295-300, 2004.