Homopolymers of l,5-dioxepan-2-one (DXO) and block copolymers of DXO and e-caprolactone (e-CL) have been synthesized with aluminum isopropoxide as an initiator in toluene and tetrahydrofuran (THF). The homopolymerization is first order with respect to both monomer and initiator, and the endgroup analysis agrees with a coordination insertion mechanism based on the acyl-oxygen cleavage of the DXO ring. Living poly(e-caprolactone) (PCL) and poly(1,5-dioxepan-2-one) (PDXO) chains are very efficient macroinitiators for the polymerization of DXO and <-CL, respectively, with formation of block copolymers of a narrow molecular weight distribution. Size-exclusion chromatography (SEC) and 13C NMR confirm the blocky structure of the copolymers, in agreement with DSC that shows a melting endotherm for the PCL block and two glass transitions characteristic of the amorphous phases of PDXO and PCL. Because of the crystallinity of the PCL block (Tm = 60 °C) and the low glass transition temperature of the amorphous PDXO block (Tg = -39 °C), poly(e-CL-fe-DXO-6-e-CL) triblocks have the potential of thermoplastic elastomers. Block copolymers of e-CL and DXO are also sensitive to hydrolysis which makes them possible candidates for biomedical applications. Initiation of the DXO polymerization with functional diethylaluminum alkoxides is also discussed.