Homopolymers of 1,4,8-trioxa[4.6]spiro-9-undecanone (TOSUO) and block copolymers of TOSUO and epsilon-caprolactone (epsilon-CL) have been synthesized with aluminum isopropoxide as an initiator in toluene at 25 degrees C. The homopolymerization is first order with respect to both monomer and initiator, and the end-group analysis agrees with a coordination-insertion mechanism based on the acyl-oxygen cleavage of the TOSUO ring. Living poly(epsilon-caprolactone) (PCL) and poly(1,4,8-trioxa[4.6]spiro-9-undecanone) (PTOSUO) chains are very efficient macroinitiators for the polymerization of TOSUO and E-CL, respectively, with formation of block copolymers of a narrow molecular weight distribution. Size-exclusion chromatography (SEC) and C-13-NMR confirm the blocky structure of the copolymers, in agreement with DSC, which shows two glass transitions characteristic of the amorphous phase of PCL and PTOSUO, respectively. The ethylene ketal pendent groups of the PTOSUO block have been successfully converted to ketones and hydroxyl pendent groups without scission of the polyester backbone. These new materials have potential for applications in medicine, surgery, and tissue engineering.