The ring-opening polymerization of oxepan-2,7-dione was initiated with 1) cationic initiators such as AlCl3and BF3· (C2H5)2O, 2) anionic initiators such as CH3COO−K+and NaH, and 3) coordination-type initiators such as stannous 2-ethylhexanoate and dibutyltin oxide. The reactions were studied at 0, 20, and 40°C in methylene chloride. Oxepan-2,7-dione was also reacted with ϵ-caprolactone (2-oxepanone) in the presence of aluminum isopropox-ide as a catalyst to generate A-B block copolymers.