1. A diblock copolymer comprising a poly(lactone) segment having a first end comprising an end group comprising the residue of an initiating alcohol and a second end comprising a terminal hydroxyl group, and a poly(propylene fumarate) segment connected to the second end of said poly(lactone) segment and formed by ring-opening copolymerization of propylene oxide and maleic anhydride initiated by said terminal hydroxyl group on said poly(lactone) segment, followed by isomerization, said diblock copolymer having a polydispersity index (Ðm) of from about 1.1 to about 1.9.